Discuss the key points for applying waterproof coatings when the substrate is moist

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Let’s discuss the key points for applying waterproof coatings on moist substrates. Typically, polyurethane waterproof coatings as well as solvent-based waterproof coatings made from polymer-modified asphalt cannot be applied properly on substrates with a moisture content of over 8%, in environments with a relative humidity of more than 80%, or on wall surfaces where condensation occurs. One way to overcome this technical challenge is by using a primer for moist substrates. A so-called moisture-barrier primer absorbs the moisture on the surface of the substrate during the curing process to form a film; it also penetrates into the capillaries within the substrate, preventing moisture from escaping from inside. It cures within approximately 2 to 8 hours. By adopting this treatment method, the technical challenges associated with applying polyurethane-based and polymer-modified asphalt solvent-based waterproof coatings in conditions of a relative humidity of nearly 100% and a substrate moisture content of 15% have been successfully overcome. The cured sealant layer adheres firmly to the cement-based substrate, with an adhesion strength of over 2 Mpa; it also exhibits good adhesion to polyurethane waterproof coatings and polymer-modified asphalt waterproof coatings, with an adhesion strength greater than 1.0 Mpa. It can be used for treating damp substrates in basements, tunnels, air-raid shelters, roofs, walls, and other similar areas. A wet substrate sealant is composed of a two-component epoxy resin and a curing agent; during application, it is mixed in the proper proportions and stirred evenly, after which it is applied to the wet substrate where it reacts with water to cure and form a film. Moisture-barrier sealants are suitable for moisture barrier treatment on wet substrates with a moisture content of over 15% ； It is also suitable for moisture barrier treatment of walls in environments with a relative humidity greater than 80% or where condensation occurs on the surface. The sealant can be applied by scraping, brushing, or rolling on a wet concrete surface 1 to 2 days after it has been poured, or on a surface covered with uncured cement mortar; normal application of the waterproof coating can then be carried out once the surface is dry. Before applying the moisture barrier on a wet substrate, first clean off any loose dust or debris from the surface of the substrate, and wipe away any standing water on it. When preparing the isolant, first stir Component A until it is well mixed, then add Component B to it (ratio of A to B = 6:0.9). Stir again until everything is homogeneous. Afterwards, use a brush, roller, or spatula to apply the prepared isolant onto the moist substrate, so as to form a uniform thin coating layer. During construction, the following points should be noted: 1. Once the two components A and B are mixed together, they cure quite rapidly; therefore, they should be prepared just before use. At 25°C, they should be used up within 0.5 hours ； 2. During application, there should be no missed areas or accumulation of material; once the surface becomes glossy and no longer sticky, normal application of the waterproof coating can proceed.