How to Improve the Crack Resistance of Waterproof Mortar
Release Time:
2020-06-08
Source:
Polymer Cement Mortar
Polymer-modified mortar is a type of mortar in which organic polymer materials replace part of the cement, with cement serving as the primary binding agent alongside the polymer. Common polymers used include polyvinyl acetate, ethylene copolymer emulsions, acrylic copolymer emulsions, and styrene–butadiene rubber emulsions. Incorporating a certain proportion of polymer can overcome the common drawbacks of ordinary mortar—significant shrinkage, high brittleness, and low bond strength—thereby effectively enhancing the mortar’s plastic deformation capacity and bond strength and markedly improving its crack resistance. However, when using polymer-modified mortar, the following issues should be carefully considered:
① In cement mortar, cement hydration requires a moist environment, whereas polymers require a dry environment to lose moisture and coalesce into a film. Therefore, the curing of polymer-modified mortar must both ensure complete cement hydration and facilitate polymer film formation; in other words, early-stage curing should be kept moist, while later-stage curing should be moderately dry.
② The higher the polymer dosage, the greater the reduction in mortar compressive strength; however, mortars formulated with different polymers exhibit varying degrees of strength. Taking polyvinyl acetate as an example, Qian Xiaoxian’s research shows that when the polymer dosage is 10–15% of the cement content and the water-to-cement ratio is around 0.4, the compressive strength of polymer-modified cement mortar decreases by approximately 30–40% compared with plain cement mortar. At the same time, both tensile strength and bond strength increase, while the modulus of deformation decreases by more than 30%.
Organosilicon Waterproof Mortar
The main component of silicone is sodium methylsiloxolate, which contains the polar –OH group and readily forms hydrogen bonds. Subsequent polycondensation reactions yield branched and network-like methylsilicone resins that interact with cement hydration products, filling the micro- and capillary pores in mortar and thereby increasing its density and impermeability. Because these methylsilicone polymer resins exhibit high plastic strength, they can reduce drying shrinkage cracks and shrinkage stresses in mortar, thus enhancing its crack resistance. Moreover, by distributing stress and preventing stress concentration, they improve the interfacial properties and plasticity of the mortar, comprehensively enhancing its tensile performance. Prior to construction, the substrate surface should be brushed with a 1:8 dilution of silicone water solution before plastering commences.
