Abstract: In order to solve the engineering problems such as migration of small molecule oil of asphalt, yellowing and discoloration of coating film, bulge delamination, weather resistance failure, etc., when traditional acrylic waterproof coating is directly applied to the base surface of old asphalt coiled materials in the old building roof renovation project, this paper prepared a high-density cross-linked acrylic lotion to prepare a special acrylic waterproof coating suitable for asphalt base surface renovation. The influence of the three core variables of lotion structure type, film thickness and ambient temperature on the oil permeability resistance, mechanical properties and appearance stability of the coating was systematically explored, and the mechanism of the migration and diffusion of asphalt oil and the barrier of acrylic acid film was revealed. The test results show that the waterproof coating prepared by self-made modified acrylic lotion has excellent comprehensive mechanical properties, with tensile strength up to 3.4 MPa, elongation at break up to 555%, and good adaptability to base deformation; Under normal temperature and natural working conditions, when the coating thickness is ≥ 1.5 mm, it can effectively block the upward migration of small molecule oils such as saturated hydrocarbons and aromatic hydrocarbons inside the asphalt, completely solving the defects of yellowing, stickiness, and discoloration in the later stage of renovating roof coatings; Under high temperature environment (>50 ℃), the thermal movement of asphalt molecules intensifies, and the impermeability of a single coating barrier decreases. It is necessary to enhance the barrier effect by thickening the coating and crosslinking modification. This study can provide theoretical basis and engineering reference for material selection, construction thickness control, and working condition adaptation of old asphalt roof non removal renovation system.
1 Introduction
In the early days, a large number of existing building roofs in China commonly used SBS modified asphalt rolls and asphalt coatings as waterproof layers. This type of waterproof system has a service life of more than 10-20 years and is subjected to UV aging, high and low temperature cycles, rainwater erosion, and base deformation for a long time. It is prone to cracking, bulging, lap joint leakage, and roll powder aging, which are the main causes of roof leakage in current urban renewal and renovation of old residential areas. The traditional roof renovation process often adopts the mode of “removing old rolls and laying new waterproof layers”, but there are disadvantages such as large demolition work, high construction waste, long construction period, high cost, and easy damage to the roof insulation layer and structural layer, which seriously restrict the efficient renovation construction of old roofs.
The renovation process of directly applying water-based waterproof coating without removing the old asphalt base has become the mainstream technical route for roof renewal at present, thanks to its advantages of convenient construction, green and low-carbon, low cost, and not damaging the original roof structure. Among them, acrylic waterproof coating has the advantages of water-based environmental protection, excellent elasticity, seamless film-forming, strong adhesion, good weather resistance, and adaptability to irregular roofs. It is extremely suitable for the renovation and reconstruction of old roof thin layers. However, engineering practice has found that ordinary acrylic coatings directly applied to aged asphalt substrates have fatal defects: the asphalt material is rich in a large amount of light oil, saturated aromatic hydrocarbons, and small glial molecules, which are easily migrated upwards under temperature gradients and capillary diffusion, penetrating into the interior and surface of the acrylic coating, ultimately causing the coating to turn yellow and discolor, become sticky locally, accumulate dust and dirt, delaminate between layers, and rapidly deteriorate water and weather resistance, seriously damaging the appearance and long-term waterproof durability of the roof after renovation.
At present, research on acrylic waterproof coatings in China mainly focuses on optimizing their mechanical properties, water resistance, aging resistance, and crack resistance. There are relatively few specialized studies on the resistance of asphalt base to oil penetration and the barrier to oil migration, and a complete material selection standard and construction control system have not yet been formed. Based on this, this paper prepared a special anti permeability oil modified acrylic lotion waterproof coating, focusing on the influence of film thickness, ambient temperature, and lotion structure on the coating’s anti permeability of asphalt oil, analyzing the mechanism of oil migration failure, defining the construction parameters and material standards suitable for the renovation of old asphalt roofs, and providing technical support for solving the common problems of yellowing, delamination, and failure of the asphalt base acrylic renovation system.
2 Experimental section
2.1 Experimental raw materials
The self-made cross-linked modified acrylic lotion, conventional commercial styrene acrylic lotion and pure acrylic lotion were used as the film forming matrix in the experiment; Add inorganic weather resistant fillers such as titanium dioxide, heavy calcium, talc powder, and water-based functional additives such as wetting and dispersing agents, defoamers, thickeners, and film-forming agents; The grassroots adopts aged SBS modified asphalt waterproofing membrane to simulate the renovation process of old roofs. All raw materials meet the requirements of the national standard GB/T 23445 for water-based building coatings, with low VOC, green and environmentally friendly properties, suitable for exposed service environments on roofs.
2.2 Sample Preparation
Put the weighed inorganic filler, deionized water, dispersant, and wetting agent into the dispersion kettle, disperse and grind at high speed until the fineness meets the standard, and prepare a uniform slurry; Then add self-made modified acrylic lotion, compare with conventional lotion, stir evenly at low speed, and add defoaming, thickening and film forming additives in turn to adjust the viscosity and workability of the system. According to the experimental gradient, apply coatings with thicknesses of 1.0 mm, 1.5 mm, and 2.0 mm on the surface of aged asphalt rolls, and cure them at room temperature for 7 days. After the coatings are fully crosslinked, perform oil resistance and mechanical performance tests.
2.3 Testing Methods
Oil permeability test: set normal temperature natural environment (25~35 ℃) and high temperature simulated environment (50~60 ℃), maintain and observe for 30 days, record yellowing, viscosity and penetration pollution on the surface of samples with different film thicknesses and different lotion systems, and evaluate the ability of the film to block asphalt oil migration;
Mechanical performance testing: According to the GB/T 16777 standard, the tensile strength and elongation at break of the coating are tested to evaluate the elasticity of the coating and its adaptability to the substrate;
Appearance stability test: Observe the surface color difference, dust, stickiness, and bulging defects of the sample to evaluate the long-term service appearance retention.
3 Experimental results and analysis
3.1 Influence of lotion type on anti oil seepage and mechanical properties
The molecular structure, cross-linking density and film forming density of different acrylic lotion are significantly different, which directly determines the oil penetration resistance and elasticity of the film. The test shows that conventional styrene acrylic lotion and ordinary pure acrylic lotion have insufficient film forming compactness, large molecular chain gap, and light asphalt oil can easily penetrate the coating. In a short period of time, the sample appears obvious yellowing, sticky surface, poor oil permeability resistance, and cannot be used for direct renovation of asphalt base surface.
The self-made modified acrylic acid lotion is modified by molecular cross-linking. After film formation, it forms a compact three-dimensional network structure. The molecular porosity is greatly reduced, which can effectively block the diffusion and penetration of small asphalt molecules. The mechanical test results show that the tensile strength of the waterproof coating system can reach 3.4 MPa, and the elongation at break is as high as 555%. The high elasticity feature can perfectly adapt to the cracking, deformation, and expansion deformation of the old roof base layer, avoiding the coating from cracking and damaging with the deformation of the base layer, and balancing waterproofing, impermeability, and structural compatibility.
3.2 Effect of Coating Thickness on Anti Oil Penetration Performance
The thickness of the coating is the core construction parameter that determines whether the asphalt oil can be completely blocked. Under natural normal temperature conditions (ambient temperature<50 ℃), coatings of different thicknesses exhibit significantly different impermeability effects. When the coating thickness is 1.0 mm, the overall thickness of the coating is thin, and there are micro pores and film defects in some areas. Asphalt oil can slowly migrate to the surface of the coating through capillary permeation. In the later stage of the test, the sample shows slight yellowing and darkening of color, and the anti permeability stability is insufficient.
When the coating thickness is increased to 1.5 mm or more, the cross-linked dense coating forms a complete, continuous, and defect free physical barrier, effectively blocking the upward diffusion channels of light oil, gum, and aromatic small molecules inside the asphalt. After 30 days of continuous observation, the surface of the sample shows no yellowing, no stickiness, no color difference, no dust pollution, and excellent oil resistance. When the thickness continues to increase to 2.0 mm, there is no significant improvement in the impermeability performance, indicating that 1.5 mm is the optimal economic thickness under normal temperature conditions, which can balance the impermeability effect, construction cost, and film stability.
3.3 Impact of Environmental Temperature on Anti Oil Penetration Performance
The environmental temperature directly affects the molecular thermal motion rate and diffusion migration ability of asphalt oil, and is an environmental variable that cannot be ignored in roof renovation. Under normal temperature and natural conditions, asphalt small molecules move slowly and have weak diffusion ability. A 1.5mm thick coating can fully achieve barrier protection. In high temperature environments (temperature>50 ℃), the temperature of roof exposure in summer is prone to reach this range, and the thermal movement of lightweight components inside asphalt is intense, resulting in a significant increase in molecular diffusion dynamics and a significant enhancement of permeability.
The high-temperature test results show that the conventional 1.5 mm thickness coating will exhibit slight oil penetration and local yellowing, and the anti-seepage barrier effect will be weakened; Under high temperature conditions, it is necessary to increase the film thickness properly and select high cross-linking density modified lotion to improve the coating compactness and barrier ability and inhibit the film failure caused by high temperature accelerated penetration. This conclusion explains the engineering phenomenon that renovation coatings on roofs exposed to high temperatures in summer are more prone to yellowing and discoloration.
Analysis of the Failure Mechanism of Asphalt Oil Penetration in Section 4
After long-term aging of old asphalt rolls, the internal polymer asphalt segments gradually break, generating a large amount of low molecular weight saturated hydrocarbons, aromatic hydrocarbons, and gum components. These small molecules have weak polarity, strong permeability, and high migration activity. Under the multiple coupling effects of roof temperature gradient, capillary pressure, and base water vapor diffusion, the light asphalt oil continues to migrate upwards. The ordinary acrylic lotion film has low cross-linking density and large film forming pores, which cannot block the penetration of small molecules. When oil is concentrated on the surface of the film, it will change the transmittance and surface state of the coating, resulting in yellowing and darkening of the film; At the same time, oily components can damage the interfacial adhesion of acrylic acid molecules, causing the coating to soften and become sticky, the surface to become dusty, and the interlayer adhesion to decrease. After long-term service, chain diseases such as delamination, bulging, and leakage may occur.
The modified cross-linked acrylic lotion builds a dense three-dimensional network structure through the cross-linking reaction in the film forming process, greatly reduces the micro pore diameter of the film layer, reduces the pore connectivity, and blocks the diffusion channel of small molecules from the physical level; At the same time, the dense coating has excellent resistance to medium penetration, which can resist the swelling and softening erosion of asphalt gum, maintain the mechanical properties and appearance stability of the coating, and achieve long-term protection of asphalt base surface.
5 Key points of engineering application control
Based on the test conclusions and engineering practice, two core parameters need to be strictly controlled for the old asphalt roof renovation construction without removal: first, the material selection, the high density cross-linked modified acrylic acid lotion system is preferred, and the use of ordinary styrene acrylic and pure acrylic low-end lotion is prohibited to avoid the problem of insufficient oil seepage resistance from the source; The second is the control of coating thickness. In areas with normal temperature climate, the coating thickness should not be less than 1.5 mm. In areas with high temperature exposure in summer and high heat in the south, the coating thickness can be appropriately increased to improve high-temperature impermeability stability. During the construction process, it is necessary to ensure that the coating is uniform and continuous, without any defects such as missed coating, pinholes, or thin coating, and to avoid oil penetration, color difference, and leakage hazards caused by local weak points.
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Post time: Sep-14-2026