In-situ repairing method for efflorescence of historical building brick wall

Abstract

The present application relates to a kind of historical building brick wall efflorescence in situ repair method, comprising the following steps: S1 disease reconnaissance and grading: the efflorescence disease of target brick wall and the weathering state of brick are multidimensional detection, and the disease grade is comprehensively judged;S2 in situ physical removal: according to disease grade matching corresponding physical removal process, remove wall efflorescence precipitate;S3 brick in situ repair;S4 air permeability and hydrophobic protection: in the surface of brick wall, construction permeable ecological inorganic nano hydrophobic material, form the hydrophobic protective layer that permeates into the capillary of brick, the hydrophobic protective layer can block liquid water migration and keep gaseous water permeation;S5 quality inspection and long-term monitoring: the brick wall after repair is carried out multi-index performance test, and periodic field monitoring is carried out.The present application realizes the systematical eradication and long-acting protection of efflorescence disease, while maintaining the historical style authenticity and air permeability of brick wall, with reversibility.

Description

Technical Field

[0001] This invention belongs to the field of protection and restoration technology of historical buildings and cultural relics, and in particular relates to an in-situ repair method for efflorescence on brick walls of historical buildings. Background Technology

[0002] Efflorescence on walls is a common problem in brick and stone structures. Essentially, it is the process by which soluble salt and alkali components within the material migrate through capillary pores to the surface and crystallize, carried by a moisture carrier. For the repair of efflorescence on exposed brick walls of historical buildings, existing techniques mostly employ acid washing, high-pressure water rinsing, or scraping and re-plastering.

[0003] Existing technical solutions generally suffer from the following drawbacks: First, they only treat the symptoms, not the root cause, and are prone to recurrence. They only treat the surface without cutting off the internal water and salt migration channels, or cause secondary damage due to the accumulation of internal moisture caused by the use of impermeable coatings. Second, they severely damage the authenticity of the historical appearance. Acid washing corrodes the brick texture, removing and rebuilding to cover up the original historical information, and color-matching to eliminate traces of time violate the core principles of "minimal intervention" and "not changing the original state" in cultural relic protection. Third, they lack reversibility. Conventional silicone and other waterproofing materials are difficult to remove without damage once applied, hindering the application of better technologies in the future. Therefore, there is an urgent need for an in-situ repair method that can eradicate efflorescence while strictly maintaining the historical appearance of the brick wall, preserving the wall's breathability, and possessing reversibility. Summary of the Invention

[0004] The main objective of this invention is to propose an in-situ repair method for efflorescence on brick walls of historical buildings, which can effectively solve the problems in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] An in-situ repair method for efflorescence on brick walls of historical buildings includes the following steps:

[0007] S1 Disease Investigation and Grading: Multi-dimensional detection of efflorescence disease and weathering status of the target brick wall is carried out to comprehensively determine the disease level.

[0008] S2 In-situ Physical Removal: Matches the corresponding physical removal process according to the severity of the disease to remove efflorescence from the wall surface;

[0009] S3 In-situ Repair of Bricks: For bricks with weathering damage, in-situ repair is carried out using materials of the same material as the original bricks, ensuring that the appearance of the repaired area is consistent with that of the original bricks.

[0010] S4 Breathable Hydrophobic Protection: A permeable ecological inorganic nano-hydrophobic material is applied to the surface of the brick wall to form a hydrophobic protective layer that penetrates into the capillary pores of the brick. The hydrophobic protective layer can block the migration of liquid water and allow gaseous water to permeate.

[0011] S5 Quality Inspection and Long-Term Monitoring: Conduct multi-indicator performance tests on the repaired brick wall and carry out periodic on-site monitoring.

[0012] Preferably, in step S1, infrared thermal imaging and visual mapping are used to create a three-dimensional disease map, a rebound hammer is used to test the surface strength of the bricks to determine the degree of weathering, and probes and endoscopes are used to detect the degree of mortar hollowing and pulverization; based on the comprehensive test results, efflorescence disease is divided into four levels:

[0013] Grade I (Mild): The surface shows white powdery precipitates without crystallization, and the brick strength is normal.

[0014] Level II (Moderate): Crystalline precipitates appear on the surface, the brick body is slightly weathered, the weathering depth is ≤2mm, and the strength reduction is <20%;

[0015] Level III Severe: Severe crystallization accompanied by brick spalling, moderate weathering of the brick with a weathering depth of 2-20mm, and a strength reduction of 20%-40%;

[0016] Level IV (Severe): The wall has structural damage, the bricks are severely weathered, the weathering depth is >20mm, and the strength reduction is >40%.

[0017] Preferably, in step S2, for Grade I mild efflorescence, a stiff-bristled brush or a bristle brush is used to directly remove the surface efflorescence; for Grade II, III, and IV efflorescence, a low-pressure pulsed airflow is first used to blow off the loose efflorescence powder on the surface, wherein the pressure of the low-pressure pulsed airflow is 0.1~0.3MPa and the pulse frequency is 2~5Hz; for the stubborn crystalline layer on the wall, a microcrystalline dry ice spraying process is used for peeling, wherein the particle size of the microcrystalline dry ice is 0.5~1.5mm, the spraying pressure is 0.2~0.4MPa, and the spraying distance from the wall is 150~250mm.

[0018] Preferably, in step S3, for lightly weathered bricks without weathering, this step can be skipped directly; for moderately and heavily weathered bricks, brick powder repair method is used; for severely weathered bricks with a weathering depth >20mm, a combination of brick patching or partial brick replacement combined with brick powder repair is used.

[0019] Preferably, the brick powder matches the physical and chemical properties of the original brick, and its color is adjusted to be similar to that of the original brick. Before repair, loose and powdery parts of the brick and surface impurities are removed. The brick powder is mixed with water to form a paste, and then one-time repair or layered repair is selected according to the repair depth. After repair, the brick is naturally cured to restore the original surface texture. Finally, a color matching agent is used to adjust the color difference between the old and new areas so that the color difference ΔE between the repaired area and the original brick is ≤1.5.

[0020] Preferably, in step S4, the solid content of the ecological inorganic nano-hydrophobic material is ≥20%, the water absorption ratio is ≤13%, the hydrophobic efficiency is ≥80%, and the penetration depth in the brick body is 3~5mm.

[0021] Preferably, in step S4, a low-pressure sprayer or brush is used for application. The spraying pressure is 0.2~0.4MPa, the spraying distance is 300~500mm, and the total coating amount is 0.1~0.3kg / m². The application is carried out in two coats. The second coat is applied after the first coat is surface dry, and the direction of the second coat is perpendicular to that of the first coat. The corners and joints of the walls are reinforced with coating.

[0022] Preferably, in step S5, the quality inspection includes five indicators: water repellency, air permeability, water absorption rate, appearance authenticity, and reversibility. The passing standards for each indicator are as follows:

[0023] Hydrophobic effect: During the water spray test, water droplets rolled off in beads, with a contact angle ≥110°;

[0024] Air permeability: Water vapor transmission rate ≥ 80% of the original brick;

[0025] Water absorption rate: 24-hour capillary water absorption rate ≤ 50% of the original brick;

[0026] Appearance authenticity: The difference from the original appearance before restoration is indistinguishable, and the color difference ΔE ≤ 1.5;

[0027] Reversibility: The hydrophobic layer can be completely removed with an alkaline solution with pH > 12 without damaging the brick.

[0028] Preferably, in step S5, the long-term monitoring period is 1, 3, 6 and 12 months after the repair. The monitoring content includes on-site appearance inspection, infrared thermal imaging internal moisture content detection, and recording of efflorescence recurrence.

[0029] This invention provides an in-situ repair method for efflorescence on brick walls of historical buildings, which has the following beneficial effects:

[0030] 1. This invention constructs a systematic repair system integrating "investigation and grading - physical removal - homogeneous repair - breathable and water-repellent - inspection and monitoring". It uses microstructure-protective physical removal methods to peel off efflorescence crystals without damaging the substrate. Combined with homogeneous repair materials that are coordinated with the original brick's physicochemical properties, it restores the surface texture. Furthermore, it forms a breathable and water-repellent barrier in the capillaries of the brick through a permeable ecological inorganic nano-hydrophobic material, cutting off the channel for liquid water to carry soluble salts to migrate outward from the source, while maintaining the wall's ability to breathe gaseous water. This achieves a systematic cure and long-term protection against efflorescence, effectively solving the technical problems of traditional repair methods that only treat the symptoms and not the root cause, and cause recurring problems.

[0031] 2. This invention adheres to the principle of authenticity preservation throughout the entire process, abandoning destructive methods such as acid washing and scraping and re-plastering. It adopts non-destructive physical cleaning processes such as low-pressure pulsed airflow and microcrystalline dry ice spraying, avoiding the corrosion of the brick surface by chemical reagents. In the repair stage, brick powder materials of the same quality as the original bricks are used, combined with color matching and transition technology, and the color difference ΔE between the repaired area and the original bricks is strictly controlled to be ≤1.5. This ensures that the repaired brick wall is highly consistent with the original appearance in terms of color, texture and historical weathering traces, thus preserving the identifiability and authenticity of the historical building to the greatest extent.

[0032] 3. The ecological inorganic nano-hydrophobic material selected in this invention has unique reversible removal characteristics. This hydrophobic protective layer can be completely removed by alkaline solutions with pH>12 without causing damage to the brick. This design breaks through the technical limitations of the irreversibility of traditional organosilicon waterproof materials, and reserves replacement space for more advanced repair technologies that may emerge in the future. It conforms to the core principles of "reversibility" and "foresight" in cultural relic protection, and also facilitates non-destructive maintenance and renewal when repair fails or materials age.

[0033] 4. This invention precisely controls the penetration depth of the hydrophobic material to 3-5mm, ensuring that it forms a hydrophobic network only within the capillary pores of the brick surface, without completely sealing the deep pore structure. Tests show that the water vapor permeability can reach more than 80% of the original brick. While ensuring excellent hydrophobic efficiency (≥80%), it also ensures the normal discharge of moisture inside the wall, avoiding secondary diseases such as internal moisture accumulation, aggravated freeze-thaw cycles, and brick powdering and peeling caused by the non-breathable coating. This significantly improves the durability and safety of the restored brick walls of historical buildings. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the steps of the in-situ repair method for efflorescence on brick walls of historical buildings according to the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0036] Reference Figure 1 This invention provides an in-situ repair method for efflorescence on brick walls of historical buildings, comprising the following steps:

[0037] S1 Disease Investigation and Grading: Multi-dimensional detection of efflorescence disease and weathering status of the target brick wall is carried out to comprehensively determine the disease level.

[0038] Specifically, infrared thermal imaging and visual mapping were used to create three-dimensional disease maps; a rebound hammer was used to test the surface strength of the bricks to determine the degree of weathering; and probes and endoscopes were used to detect the degree of mortar hollowing and pulverization. Based on the comprehensive test results, efflorescence disease was classified into four levels:

[0039] Grade I (Mild): The surface shows white powdery precipitates without crystallization, and the brick strength is normal.

[0040] Level II (Moderate): Crystalline precipitates appear on the surface, the brick body is slightly weathered, the weathering depth is ≤2mm, and the strength reduction is <20%;

[0041] Level III Severe: Severe crystallization accompanied by brick spalling, moderate weathering of the brick with a weathering depth of 2-20mm, and a strength reduction of 20%-40%;

[0042] Level IV (Severe): The wall has structural damage, the bricks are severely weathered, the weathering depth is >20mm, and the strength reduction is >40%.

[0043] Infrared thermal imaging technology utilizes differences in surface temperature distribution in brick walls to identify areas with abnormal internal moisture content and thermal defects. It can non-contactly acquire the distribution of hidden defects over large areas of the wall, providing macroscopic planar data support for creating three-dimensional defect maps. Visual mapping records apparent cracks, salt deposits, and historical repair traces, correcting misjudgments in infrared images and supplementing texture information. A rebound hammer quantitatively characterizes the degradation of mechanical properties caused by weathering by testing the rebound value of the brick surface, transforming subjective perceptions of weathering into objective strength loss data. Probes and endoscopes penetrate deep into brick joints or drill holes to directly examine the bonding state of the mortar layer, the extent of hollow areas, and deep pulverization, compensating for the limitations of surface inspection in reaching the internal structure. These three methods acquire data from three dimensions—moisture field, mechanical field, and structural integrity—and, after cross-validation, form a three-dimensional portrait of the brick wall's health condition.

[0044] S2 In-situ Physical Removal: Matches the corresponding physical removal process according to the severity of the disease to remove efflorescence from the wall surface;

[0045] Specifically, for Grade I mild efflorescence, a stiff-bristled brush or bristle brush is used to directly remove the surface efflorescence. Since Grade I efflorescence only manifests as a white powdery exudate adhering to the brick surface and has not yet formed a dense crystalline shell, it can be effectively removed with low-energy mechanical friction. The use of a stiff-bristled brush or bristle brush instead of a metal brush or electric polishing tool aims to avoid irreversible mechanical scratches to the precious original patina and weathering marks on the surface of the historical brick wall during the removal process, reflecting a moderate cleaning strategy under the principle of minimal intervention.

[0046] For Class II, III, and IV efflorescence, a low-pressure pulsed airflow is first used to remove loose efflorescence powder from the surface. The pressure of the low-pressure pulsed airflow is 0.1~0.3MPa, and the pulse frequency is 2~5Hz. This parameter window is set based on a dual balance between removal efficiency and substrate safety. When the airflow pressure is below 0.1MPa, its kinetic energy is insufficient to overcome the interlocking force between moderate to severe efflorescence powder and pores, resulting in incomplete removal. When the pressure exceeds 0.3MPa, for Class III or IV bricks that already have weathering damage, the shear force of the high-speed airflow can easily induce the peeling of the powdery areas or even cause new microcracks. Meanwhile, the use of a 2-5Hz pulse mode instead of a continuous steady-state airflow takes advantage of the fatigue effect and instantaneous peak characteristics of pulsating load: the pressure peak generated by the pulsed airflow in a very short time can effectively loosen salt particles embedded deep in the capillaries, while the interval allows the airflow to dissipate heat and prevent excessive local negative pressure. Compared with the continuous airflow of the same average pressure, it significantly reduces the cumulative damage to fragile substrates and consumes less energy.

[0047] For stubborn crystalline layers on walls, a microcrystalline dry ice blasting process is used for peeling. The microcrystalline dry ice particles have a diameter of 0.5~1.5mm, a blasting pressure of 0.2~0.4MPa, and a blasting distance of 150~250mm from the wall surface. The core mechanism of this process lies in the synergistic effect of the low-temperature embrittlement effect of dry ice particles and the impact of kinetic energy. The dry ice particles have a temperature as low as -78.5℃. When they impact the brick surface, the salt crystals in the contact area shrink in volume due to rapid cooling. Because of the significant difference in the thermal expansion coefficients between the salt crystals and the brick matrix, this non-coordinated deformation generates huge shear stress at the interface, causing the crystalline layer to crack from the inside and detach from the substrate. In this process, the particle size range of 0.5~1.5mm is crucial: if the particle size is too small, the kinetic energy of a single particle is insufficient to trigger effective embrittlement and peeling; if the particle size is too large, it will act like abrasive in sandblasting, causing cutting and wear on the brick surface and destroying the original texture. A spray pressure of 0.2~0.4MPa ensures that the particles have sufficient flight speed to maintain a low temperature and transmit impact force, while avoiding substrate erosion caused by excessive pressure. A spray distance of 150~250mm is the optimal process range verified by experiments: if the distance is too close, the dry ice particles are not sufficiently accelerated, and the concentrated cold energy can easily damage the brick surface; if the distance is too far, the dry ice will excessively sublimate during flight, losing its phase change heat absorption capacity by the time it reaches the wall, degenerating into ordinary gas purging, and failing to achieve the embrittlement and peeling of the crystalline layer. It should be understood that the above parameter combination constitutes a technical barrier distinct from traditional high-pressure water jet washing or chemical acid washing, achieving precise removal without introducing water, leaving chemical residues, or damaging the brick's microstructure.

[0048] S3 In-situ Repair of Bricks: For bricks with weathering damage, in-situ repair is carried out using materials of the same material as the original bricks, ensuring that the appearance of the repaired area is consistent with that of the original bricks.

[0049] Specifically, for lightly weathered bricks, skip this step; for moderately and heavily weathered bricks, use brick powder repair; for severely weathered bricks with a weathering depth >20mm, use a combination of brick patching or partial brick replacement with brick powder repair.

[0050] For Class I lightly weathered bricks, although the surface may be slightly powdery, the overall structure remains intact. Excessive repair would damage the original patina and historical coating, so skipping the repair process is the best option for preserving authentic historical information. For Class II and Class III moderately to severely weathered bricks, although there are surface defects or peeling, the bricks still possess sufficient load-bearing capacity. In this case, brick powder repair can restore surface integrity while avoiding the loss of historical information caused by large-scale replacement. For Class IV severely weathered bricks, when the weathering depth exceeds 20mm, the effective cross-section of the brick is significantly weakened. Simply relying on brick powder filling is insufficient to guarantee long-term stability. Structural reinforcement measures such as inlaying brick pieces or partial brick replacement must be introduced, supplemented by brick powder repair for surface transition treatment, to ensure that the repaired wall meets mechanical safety requirements while maintaining visual harmony and unity.

[0051] The brick powder is matched with the physical and chemical properties of the original brick, and its color is adjusted to be similar to that of the original brick. Before repair, loose and powdery parts of the brick and surface impurities are removed. The brick powder is mixed with water to form a paste. Depending on the depth of the repair, one-time repair or layered repair is selected. After repair, it is naturally cured to restore the surface texture of the original brick. Finally, a color matching agent is used to adjust the color difference between the old and new areas so that the color difference ΔE between the repaired area and the original brick is ≤1.5.

[0052] S4 Breathable Hydrophobic Protection: A permeable ecological inorganic nano-hydrophobic material is applied to the surface of the brick wall to form a hydrophobic protective layer that penetrates into the capillary pores of the brick. The hydrophobic protective layer can block the migration of liquid water and allow gaseous water to permeate.

[0053] Specifically, this invention uses an eco-friendly inorganic nano-hydrophobic material developed by 20th Metallurgical Construction Co., Ltd., which is derived from the patent "A Soil Hydrophobic Emulsion and Its Preparation Method and Application", patent number CN202311740949.0. The hydrophobic emulsion is a hydrophobic material that can be mixed into the soil or sprayed on the wall. The solid content of the eco-friendly inorganic nano-hydrophobic material is ≥20%, the water absorption ratio is ≤13%, the hydrophobic efficiency is ≥80%, and the penetration depth in the brick is 3~5mm.

[0054] The performance indicators set in this series were not chosen arbitrarily, but rather represent the optimal window determined through extensive experimental verification based on the specific needs of protecting historical building brick walls. Specifically, a solid content of ≥20% ensures that the material, even after dilution, still has sufficient effective components to form a continuous and dense nano-hydrophobic film on the inner wall of the capillaries, preventing water seepage channels caused by discontinuous film formation due to excessively low concentration. A water absorption ratio of ≤13% and a hydrophobic efficiency of ≥80% are the core quantitative standards for measuring the protective effect, ensuring that when the treated brick is exposed to rain or high humidity, liquid water cannot penetrate the substrate through capillary action, thus cutting off the water carrier conditions for efflorescence at the source. Crucially, the penetration depth range of 3-5mm constitutes the physical basis for achieving the functional balance of "breathable but impermeable" in this invention. If the penetration depth is less than 3mm, the hydrophobic layer is too thin and cannot resist external mechanical wear or long-term weathering erosion, significantly shortening the protective lifespan. If the penetration depth is greater than 5mm, the material may overfill the deep pores of the brick. Although the hydrophobicity is enhanced, it will greatly reduce the water vapor permeability, preventing moisture from escaping from the wall and inducing secondary damage such as freeze-thaw damage or salt crystal expansion. A penetration depth of 3-5mm ensures that the hydrophobic network is distributed only within the capillary channels of the brick surface, forming an effective liquid water barrier while retaining the deep pores as channels for gaseous water transport, perfectly balancing the dual needs of water-blocking protection and breathability.

[0055] After determining the material performance benchmarks, meticulous control of the construction process is crucial to ensuring the effectiveness of the protection. In step S4, a low-pressure sprayer or brush is used for application. The spraying pressure is 0.2~0.4MPa, the spraying distance is 300~500mm, and the total coating amount is 0.1~0.3kg / m². The application is done in two coats. After the first coat is surface dry, the second coat is applied, and the direction of the second coat is perpendicular to that of the first coat. Corners and wall joints are given extra coating treatment.

[0056] The use of low-pressure spraying (0.2-0.4 MPa) instead of high-pressure spraying is to prevent micro-damage caused by high-speed liquid flow impacting the weathered and fragile brick surface, while also avoiding material loss due to excessively fine atomization. A spraying distance of 300-500 mm ensures that the droplets have appropriate kinetic energy and spreading area upon reaching the wall, evenly covering the uneven texture of the historical brick surface without causing drips due to insufficient distance or dry spray failure due to excessive distance. The total coating amount of 0.1-0.3 kg / m² is based on the saturation absorption threshold calculated from the brick porosity and material solid content. Below this value, a complete protective layer is difficult to form; above this value, excess film will form on the surface, altering the original gloss and texture of the brick wall. The two-coat, perpendicularly oriented process design aims to eliminate missed areas and shadows inherent in unidirectional brushing, ensuring the continuity and uniformity of the hydrophobic film in three-dimensional space through orthogonal superposition. The first coat is considered dry when it's no longer sticky to the touch. This indicates that the solvent has evaporated and the nanoparticles are initially anchored to the pore walls. Applying a second coat at this point allows for a strong physical bond between the two layers, rather than simple stacking, thus enhancing overall adhesion. Corners and seams, due to their complex geometry, stress concentration, and susceptibility to water accumulation, are weak points in the protective layer and require additional coating to compensate for any insufficient coverage that may occur with conventional application.

[0057] In addition to its excellent protective performance and construction adaptability, the eco-friendly inorganic nano-hydrophobic material selected in this embodiment also possesses unique reversibility, which is its essential advantage over traditional silicone waterproof coatings. Specifically, this hydrophobic protective layer can be completely removed by an alkaline solution with a pH > 12, and the removal process does not cause any chemical corrosion or physical damage to the brick. This reversible design has profound significance for the protection of historical buildings: on the one hand, it reserves replacement space for more advanced and compatible repair technologies that may emerge in the future, avoiding the predicament of "spilled water cannot be recovered" due to the aging or performance limitations of current materials; on the other hand, when the repair effect does not meet expectations or local abnormalities occur, the original hydrophobic layer can be removed and reconstructed without resorting to destructive methods such as mechanical grinding or strong acid etching as used for silicone coatings. In actual engineering verification, samples of the brick wall 12 months after repair were taken for reversibility testing. After soaking and cleaning with sodium hydroxide solution at pH=13, the contact angle returned to the hydrophilic state before treatment, and the microscopic morphology of the brick surface under a microscope showed no change. This fully demonstrates the technical reliability of the material in maintaining complete reversibility after long-term use.

[0058] S5 Quality Inspection and Long-Term Monitoring: Conduct multi-indicator performance tests on the repaired brick wall and carry out periodic on-site monitoring.

[0059] Quality inspection includes five indicators: water repellency, air permeability, water absorption, appearance authenticity, and reversibility. The passing standards for each indicator are as follows:

[0060] Hydrophobic effect: During the water spray test, water droplets rolled off in beads, with a contact angle ≥110°;

[0061] Air permeability: Water vapor transmission rate ≥ 80% of the original brick;

[0062] Water absorption rate: 24-hour capillary water absorption rate ≤ 50% of the original brick;

[0063] Appearance authenticity: The difference from the original appearance before restoration is indistinguishable, and the color difference ΔE ≤ 1.5;

[0064] Reversibility: The hydrophobic layer can be completely removed with an alkaline solution with pH > 12 without damaging the brick.

[0065] These five indicators constitute a multi-dimensional performance evaluation system, aiming to comprehensively verify the restoration effect from three aspects: functional effectiveness, material compatibility, and cultural relic protection ethics, thus avoiding the risk of one-sidedness that may arise from evaluating a single indicator. Among them, the water-repellent effect, air permeability, and water absorption rate indicators focus on verifying whether the protective layer has successfully achieved the core functional goal of "liquid resistance and air permeability"; the appearance authenticity indicator is used to confirm whether the restoration process strictly follows the principle of minimal intervention and does not cause visual interference with historical information; and the reversibility indicator is the key feature that distinguishes this invention from traditional irreversible restoration technologies, ensuring that the current restoration measures will not become an obstacle to the application of better technologies in the future.

[0066] Specifically, for the above five indicators, this invention clarifies specific qualification standards and corresponding test methods to ensure the reproducibility and objectivity of the test results. The qualification standards for each indicator are as follows: Regarding water repellency, water droplets must roll off in a bead-like fashion during the water spray test, with a contact angle ≥110°. The water spray test is a direct, rapid, on-site qualitative testing method, judging the continuity of the water-repellent layer by observing the shape of water droplets on the wall surface; while the contact angle measurement provides a quantitative characterization of wettability. The threshold setting of ≥110° is an effective water repellency boundary determined based on a large amount of experimental data; below this value, liquid water may still slowly seep in under wind pressure or capillary action. Regarding air permeability, the water vapor transmission rate must be ≥80% of the original brick body. This indicator is tested using the wet cup method, i.e., the test brick sample is covered at the opening of a sealed container, and the transmission rate is calculated by weighing the mass of water vapor that permeates the brick sample over a certain period of time. Setting a lower limit of 80% ensures that the protective layer does not significantly hinder the expulsion of moisture from inside the wall, preventing freeze-thaw damage or salt crystallization expansion caused by water vapor accumulation. Regarding water absorption, the capillary water absorption rate must be ≤50% of the original brickwork within 24 hours. This indicator is measured using the Karsten tube method, simulating the continuous action of rainwater on the wall surface under wind pressure. The ≤50% limit means that the protective layer reduces the amount of water intrusion by at least half, inhibiting the water carrier conditions for efflorescence at the source. Regarding the authenticity of appearance, the difference from the original appearance before restoration must be indistinguishable, and the color difference ΔE ≤1.5. Testing combines visual observation with quantitative detection using a colorimeter. ΔE ≤1.5 is the critical value at which the human eye cannot distinguish color differences. This stringent standard ensures a high degree of color integration between the repaired area and the original wall surface, maintaining the overall stylistic harmony of the historical building.

[0067] Beyond the aforementioned conventional performance indicators, reversibility verification is the most unique and crucial aspect of the quality inspection system in this embodiment. Specifically, reversibility requires that the hydrophobic layer can be completely removed by an alkaline solution with a pH > 12, without damaging the brick after removal. This test must be conducted in a laboratory environment: core samples are drilled from inconspicuous areas after repair or samples are taken from test blocks under the same conditions, and these samples are immersed in a sodium hydroxide or potassium hydroxide solution with a pH > 12 for a certain period of time (usually 24-48 hours), followed by rinsing with clean water and drying. The judgment criteria include two aspects: first, confirming through contact angle testing that the hydrophobicity has completely disappeared and returned to the hydrophilic state before treatment; second, confirming through microscopic observation and strength testing that the microstructure and mechanical properties of the brick surface have not deteriorated. This verification step directly addresses the core requirement of "reversibility" in cultural relic protection, proving that the ecological inorganic nano-hydrophobic material used in this invention is different from organosilicon resins that form permanent cross-linked networks. Its chemical bonding mode allows it to be gently broken under specific alkaline conditions, thus reserving a safe channel for possible future material updates or repair corrections. If we only focus on the water-repellent and air-permeable properties while ignoring the reversibility verification, we cannot demonstrate the unique value and technological advancement of this invention in the field of cultural heritage protection.

[0068] In addition to immediate quality inspection, step S5 establishes a systematic long-term monitoring mechanism to verify the durability and stability of the repair effect. Specifically, the long-term monitoring period is 1, 3, 6, and 12 months after the repair. The monitoring content includes on-site visual inspection, infrared thermal imaging internal moisture content detection, and recording of efflorescence recurrence.

[0069] This invention constructs a systematic repair system integrating "investigation and grading, physical removal, homogeneous repair, breathable and water-repellent material, and inspection and monitoring." It utilizes microstructure-protective physical removal methods to peel off efflorescence crystals without damaging the substrate. Combined with homogeneous repair materials that are compatible with the original brick's physicochemical properties, it restores the surface texture. Furthermore, it forms a breathable and water-repellent barrier within the brick's capillaries through a permeable ecological inorganic nano-hydrophobic material, cutting off the channel for liquid water carrying soluble salts to migrate outwards at the source. Simultaneously, it maintains the wall's ability to breathe gaseous water, thereby achieving a systematic cure and long-term protection against efflorescence. This effectively solves the technical problems of traditional repair methods that only treat the symptoms and not the root cause, leading to recurring efflorescence.

[0070] This invention adheres to the principle of authenticity preservation throughout the entire process, abandoning destructive methods such as acid washing and scraping and re-plastering. Instead, it employs non-destructive physical cleaning processes such as low-pressure pulsed airflow and microcrystalline dry ice blasting, avoiding the corrosion of the brick surface by chemical reagents. In the repair stage, brick powder materials of the same quality as the original bricks are used, combined with color matching and transition technology, to strictly control the color difference ΔE between the repaired area and the original bricks to ≤1.5. This ensures that the repaired brick wall is highly consistent with the original appearance in terms of color, texture, and historical weathering marks, thus preserving the identifiability and authenticity of the historical building to the greatest extent possible.

[0071] The ecological inorganic nano-hydrophobic material selected in this invention has unique reversible removal characteristics. This hydrophobic protective layer can be completely removed by alkaline solutions with pH > 12 without damaging the brick. This design breaks through the technical limitations of the irreversibility of traditional organosilicon waterproof materials, and reserves replacement space for more advanced repair technologies that may emerge in the future. It conforms to the core principles of "reversibility" and "foresight" in cultural relic protection, and also facilitates non-destructive maintenance and renewal when repair fails or materials age.

[0072] This invention precisely controls the penetration depth of the hydrophobic material to 3-5mm, ensuring that it forms a hydrophobic network only within the capillary pores of the brick surface, without completely sealing the deep pore structure. Tests show that the water vapor permeability can reach more than 80% of the original brick. While ensuring excellent hydrophobic efficiency (≥80%), it also ensures the normal discharge of moisture from inside the wall, avoiding secondary problems such as internal moisture accumulation, aggravated freeze-thaw cycles, and brick powdering and peeling caused by the impermeable coating. This significantly improves the durability and safety of the restored brick walls of historical buildings.

[0073] The technical solution of the present invention will be further described below with reference to specific embodiments and comparative examples.

[0074] Comparative example (existing technical method)

[0075] A brick wall with efflorescence was selected as the control test object. The conventional repair method of acid washing + organosilicon waterproofing was adopted. The specific process is as follows:

[0076] Surface cleaning: Use a 5% oxalic acid solution to scrub the efflorescent area. After the reaction is complete, rinse with clean water and let it air dry.

[0077] Waterproofing treatment: Apply a coat of commercially available standard silicone waterproof coating to the dried wall surface.

[0078] Repair Results and Defects: Three months after the repair was completed, blistering appeared under the coating, and localized efflorescence recurred; the acid washing process caused corrosion and whitening of the brick surface, damaging the original texture and surface grain; the silicone coating formed a continuous film on the wall, completely covering the original color and historical weathering marks of the brick, giving the wall a uniform "new wall" appearance, which seriously violated the principle of protecting the authenticity of historical buildings; at the same time, the excessive density of the coating caused the wall to lose its breathability, and the internal moisture could not dissipate normally, which could easily cause secondary structural damage such as brick freeze-thaw and mortar hollowing.

[0079] Example 1: Repair of efflorescence on exposed brick walls of modern historical buildings

[0080] This example applies to a historical brick-and-wood structure building dating back to the 1920s. The exterior walls are made of exposed red brick, and multiple areas show efflorescence, with some areas reaching a height of 0.3 to 1.2 meters, accompanied by varying degrees of brick weathering. The restoration process is as follows:

[0081] Step S1: Disease Investigation and Classification

[0082] Infrared thermal imaging was used to detect the moisture content of the wall surface, and the moisture content of the efflorescence area was 15%~20%. XRD phase analysis determined that the efflorescence precipitates were mainly Ca(OH)2 and CaSO4·2H2O. The surface strength of the bricks was tested using a rebound hammer, and the strength of the bricks was reduced by about 30% compared with the intact bricks. Based on the results of visual mapping, probe and endoscopy, the efflorescence disease in this area was comprehensively judged to be Grade III (severe).

[0083] Step S2: In-situ physical removal

[0084] First, a low-pressure pulsed airflow is used to blow away the loose efflorescent powder on the surface. The airflow pressure is 0.2 MPa and the pulse frequency is 3 Hz. For the stubborn crystalline layer on the wall, a microcrystalline dry ice blasting process is used to peel it off. The dry ice particle size is 0.5~1.5 mm, the blasting pressure is 0.2~0.4 MPa, and the nozzle distance from the wall is 150~250 mm. The low-temperature embrittlement effect is used to completely peel off the crystalline layer without damaging the original microstructure and surface texture of the brick.

[0085] Step S3: In-situ repair of bricks

[0086] For moderately and severely weathered bricks, brick powder repair method is used; for severely damaged areas with a weathering depth greater than 20mm, a combination of inlaying brick pieces of the same material and brick powder repair is used.

[0087] Before repair, remove any loose or powdery parts of the brick and clean the surface of oil and dust. Use brick powder that matches the physical and chemical properties of the original brick and mix it with water to form a paste. Depending on the depth of the damage, choose to repair in one go or in layers. During the repair process, restore the original surface texture of the brick. After the repair is completed, allow it to cure naturally. Finally, use a color matching agent to adjust the color difference between the old and new areas to ensure a natural transition. The color difference should be controlled to ΔE≤1.5.

[0088] Step S4: Breathable and hydrophobic protection

[0089] Ecological inorganic nano-hydrophobic material (20% solid content, hydrophobic efficiency ≥80%) is used for spraying. The total coating amount is 0.3 kg / m², applied in two coats, with a material penetration depth of 3 mm. After the first coat is surface dry (not sticky to the touch), the second coat is applied perpendicular to the first, reinforcing weak areas such as corners and grout lines. Avoid water contact with the wall surface for 24 hours after application and allow it to cure for 7 days to achieve the best hydrophobic effect.

[0090] Step S5: Quality Inspection and Long-Term Monitoring

[0091] After the repair was completed, performance tests were conducted: In the water spray test, water droplets rolled off in a spherical shape, and the surface contact angle was 118°; the water vapor transmission rate measured by the wet cup method was 85% of that of the original brick; the 24-hour water absorption rate measured by the Karsten tube capillary water absorption test was 42% of that of the original brick; after colorimeter detection and 3D scanning comparison, the color difference between the repaired area and the original wall surface was ΔE=1.2, and the appearance difference was indistinguishable.

[0092] Follow-up visits were conducted at 1, 3, 6 and 12 months after the restoration. Infrared thermal imaging showed that the internal moisture content of the wall was stable, there was no recurrence of efflorescence, and the historical appearance of the wall was well preserved.

[0093] Example 2: Repair of efflorescence on exposed brick walls in antique-style buildings

[0094] This example is applied to an antique-style building in an urban renewal project. The building walls are 370mm thick exposed brick walls. Due to excessively high alkali content in the mortar used for masonry, the entire wall surface has efflorescence, although the bricks themselves show no weathering damage. The repair process is as follows:

[0095] Step S1: Disease Investigation and Classification

[0096] Infrared thermal imaging showed that the moisture content of the efflorescence area was 12%–18%; XRD phase analysis determined that the efflorescence precipitates were mainly Ca(OH)2; the brick resilience showed no significant decrease, and there were no weathering defects. Based on these findings, the efflorescence damage in this area was classified as Grade I (mild).

[0097] Step S2: In-situ physical removal

[0098] Use a stiff-bristled brush to evenly remove efflorescent powder from the wall surface and clean away any dust. Do not use any chemical cleaning agents throughout the process to avoid damaging the brick surface.

[0099] Step S3: In-situ repair of bricks

[0100] Since the bricks have normal strength and no weathering defects, this step is omitted.

[0101] Step S4: Breathable and hydrophobic protection

[0102] Ecological inorganic nano-hydrophobic material (20% solid content, hydrophobic efficiency ≥80%) is used for spraying. The total coating amount is 0.25 kg / m², and it is applied in two coats, with a material penetration depth of 3 mm. After the first coat is surface dry, the second coat is sprayed vertically to ensure uniform coverage of the wall surface.

[0103] Step S5: Quality Inspection and Long-Term Monitoring

[0104] Performance test results after repair: Water droplets rolled off quickly during the water spray test, with a surface contact angle of 121°; water vapor transmission rate was 88% of the original brick; capillary water absorption rate was 18% of the original brick; and there was no visually noticeable difference between the wall surface and the unrepaired area.

[0105] A follow-up visit 12 months after the repair showed no recurrence of efflorescence on the wall, and the appearance remained stable.

[0106] In summary, through comparative verification with two sets of engineering examples, the in-situ repair method for efflorescence on brick walls of historical buildings described in this invention constructs a systematic repair system integrating "investigation and grading - physical removal - homogeneous repair - breathability and water repellency - inspection and monitoring". This system can specifically address the core defects of existing efflorescence repair technologies, such as treating the symptoms but not the root cause, damaging the historical appearance, and easily causing secondary diseases.

[0107] Compared to conventional solutions involving acid washing and adding film-type waterproof coatings, this method removes efflorescence entirely through physical means, avoiding the corrosion and texture damage to the brick surface caused by chemical reagents. It employs a permeable, eco-friendly, inorganic, nano-hydrophobic material to achieve a "breathable but waterproof" protective effect. This not only blocks the capillary channels for water and salt migration at the source, effectively inhibiting efflorescence recurrence, but also preserves the wall's ability to dissipate moisture, preventing secondary damage such as brick powdering and mortar hollowing caused by internal moisture accumulation. Furthermore, the hydrophobic layer is reversibly removable, aligning with the core principles of cultural relic protection: "minimal intervention, traceability, and renewability."

[0108] The two sets of implementation examples respectively cover two typical application scenarios: modern historical buildings with severe efflorescence and brick weathering, and antique-style buildings with mild efflorescence but no weathering. After restoration, both achieved a long-term protective effect of no efflorescence recurrence for 12 months. The wall appearance was indistinguishable from the original, and the water vapor permeability of the wall remained above 85% of the original brick. All performance indicators met the design requirements. This method allows for flexible adjustment of procedures and parameters according to the severity of the damage, making it highly adaptable. It can be widely applied to in-situ restoration projects of exposed brick walls with efflorescence in cultural relics buildings, historical buildings, historical districts, and antique-style buildings, combining engineering practicality with cultural preservation value.

[0109] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for in-situ repair of efflorescence on brick walls of historical buildings, characterized in that, Includes the following steps: S1 Disease Investigation and Grading: Multi-dimensional detection of efflorescence disease and weathering status of the target brick wall is carried out to comprehensively determine the disease level. S2 In-situ Physical Removal: Matches the corresponding physical removal process according to the severity of the disease to remove efflorescence from the wall surface; S3 In-situ Repair of Bricks: For bricks with weathering damage, in-situ repair is carried out using materials of the same material as the original bricks, ensuring that the appearance of the repaired area is consistent with that of the original bricks. S4 Breathable Hydrophobic Protection: A permeable ecological inorganic nano-hydrophobic material is applied to the surface of the brick wall to form a hydrophobic protective layer that penetrates into the capillary pores of the brick. The hydrophobic protective layer can block the migration of liquid water and allow gaseous water to permeate. S5 Quality Inspection and Long-Term Monitoring: Conduct multi-indicator performance tests on the repaired brick wall and carry out periodic on-site monitoring.

2. The in-situ repair method for efflorescence on brick walls of historical buildings according to claim 1, characterized in that, In step S1, infrared thermal imaging and visual mapping are used to create a three-dimensional disease map. A rebound hammer is used to test the surface strength of the bricks to determine the degree of weathering. Probes and endoscopes are used to detect the degree of mortar hollowing and pulverization. Based on the comprehensive test results, efflorescence disease is divided into four levels: Grade I (Mild): The surface shows white powdery precipitates without crystallization, and the brick strength is normal. Level II (Moderate): Crystalline precipitates appear on the surface, the brick body is slightly weathered, the weathering depth is ≤2mm, and the strength reduction is <20%; Level III Severe: Severe crystallization accompanied by brick spalling, moderate weathering of the brick with a weathering depth of 2-20mm, and a strength reduction of 20%-40%; Level IV (Severe): The wall has structural damage, the bricks are severely weathered, the weathering depth is >20mm, and the strength reduction is >40%.

3. The in-situ repair method for efflorescence on brick walls of historical buildings according to claim 2, characterized in that, In step S2, for Grade I mild efflorescence, a stiff-bristled brush or a bristle brush is used to directly remove the surface efflorescence; for Grade II, III, and IV efflorescence, a low-pressure pulsed airflow is first used to blow off the loose efflorescence powder on the surface. The pressure of the low-pressure pulsed airflow is 0.1~0.3MPa, and the pulse frequency is 2~5Hz; for the stubborn crystalline layer on the wall, a microcrystalline dry ice spraying process is used for peeling. The particle size of the microcrystalline dry ice is 0.5~1.5mm, the spraying pressure is 0.2~0.4MPa, and the spraying distance from the wall is 150~250mm.

4. The in-situ repair method for efflorescence on brick walls of historical buildings according to claim 1, characterized in that, In step S3, skip this step for lightly weathered bricks without weathering, use brick powder repair for moderately and heavily weathered bricks, and use a combination of brick patching or partial brick replacement combined with brick powder repair for severely weathered bricks with a weathering depth >20mm.

5. The in-situ repair method for efflorescence on brick walls of historical buildings according to claim 4, characterized in that, The brick powder is matched with the physical and chemical properties of the original brick, and its color is adjusted to be similar to that of the original brick. Before repair, loose and powdery parts of the brick and surface impurities are removed. The brick powder is mixed with water to form a paste. Depending on the depth of the repair, one-time repair or layered repair is selected. After repair, it is naturally cured to restore the surface texture of the original brick. Finally, a color matching agent is used to adjust the color difference between the old and new areas so that the color difference ΔE between the repaired area and the original brick is ≤1.

5.

6. The in-situ repair method for efflorescence on brick walls of historical buildings according to claim 1, characterized in that, In step S4, the solid content of the ecological inorganic nano-hydrophobic material is ≥20%, the water absorption ratio is ≤13%, the hydrophobic efficiency is ≥80%, and the penetration depth in the brick body is 3~5mm.

7. The in-situ repair method for efflorescence on brick walls of historical buildings according to claim 6, characterized in that, In step S4, a low-pressure sprayer or brush is used for application. The spraying pressure is 0.2~0.4MPa, the spraying distance is 300~500mm, and the total coating amount is 0.1~0.3kg / m². The application is done in two coats. The second coat is applied after the first coat is surface dry, and the direction of the second coat is perpendicular to that of the first coat. The corners and joints of the walls are reinforced with coating.

8. The in-situ repair method for efflorescence on brick walls of historical buildings according to claim 1, characterized in that, In step S5, the quality inspection includes five indicators: water repellency, air permeability, water absorption rate, appearance authenticity, and reversibility. The passing standards for each indicator are as follows: Hydrophobic effect: During the water spray test, water droplets rolled off in beads, with a contact angle ≥110°; Air permeability: Water vapor transmission rate ≥ 80% of the original brick; Water absorption rate: 24-hour capillary water absorption rate ≤ 50% of the original brick; Appearance authenticity: The difference from the original appearance before restoration is indistinguishable, and the color difference ΔE ≤ 1.5; Reversibility: The hydrophobic layer can be completely removed with an alkaline solution with pH > 12 without damaging the brick.

9. The in-situ repair method for efflorescence on brick walls of historical buildings according to claim 1, characterized in that, In step S5, the long-term monitoring period is 1, 3, 6 and 12 months after the repair. The monitoring content includes on-site appearance inspection, infrared thermal imaging internal moisture content detection, and recording of efflorescence recurrence.

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