Shrinkage hole of coating is a common problem in floor construction
Concrete sealing hardener
Coating shrinkage is one of the common problems in floor construction, which will lead to floor surface defects, affect the gloss and stain resistance, and greatly reduce the aesthetics and practicability of the floor.There are many reasons for coating surface shrinkage.
First, the formation of shrinkage cavity
The surface defects of the coating mainly include sag, pinhole, shrinkage or too thick corner and so on.There are two kinds of depressions on the surface of the film, one is circular and the other is hexagonal.The sag of the film surface consists of a gradient of surface tension.Due to changes in coating composition and temperature, surface tension is not uniform and fluid flows from the bottom surface tension to the high surface tension.As a result, depressions are formed on the surface of the fluid, and the circular shrinkage cavity is formed by the central depression of the edge bulge, or the Bernardo vortex is formed by the central depression of the edge bulge and the hexagonal groove.There is a material with bottom tension in the center of the shrinkage cavity, and the surface tension difference between it and the surrounding coating is the driving force for the formation of the shrinkage cavity, which causes the surrounding liquid and fluid to deviate from each other to form the shrinkage cavity.
The coating will form shrinkage holes in the process of construction and drying, and there are problems of cleaning the coating itself and substrate.The surface tension of the coating is not uniform due to the presence of droplets of low surface tension on the coating itself or the presence of low surface tension areas on the coating surface due to contamination.Under the action of the surface tension difference, the coating flows from low surface tension to high surface tension, resulting in the formation of a central depression of holes - shrinkage cavity.The uneven surface tension is caused by internal causes.In fact, some of the properties of paint itself, such as paint viscosity, thixotropy, paint drying speed, film thickness, will aggravate or weaken the flow ability of paint fluid, thereby aggravating or weakening shrinkage degree, these factors are attributed to external causes.Internal cause is the inevitable condition of shrinkage cavity, and external cause can properly control or aggravate the degree of shrinkage cavity.
After coating construction, in the process of dry film formation, the evaporation of surface solvent, surface polymer concentration and the increase of coating viscosity will lead to surface tension and surface density more than the volume, the formation of depression.Generally speaking, the flow of thick smear (>4mm) is mainly driven by density gradient, and the thin liquid coating is controlled by surface tension gradient, forming shrinkage cavity.
Two, the harm of coating shrinkage hole
The existence of pinhole and shrinkage hole not only affects the appearance of the coating, it is difficult to pass the acceptance of the coating, but also seriously affects the waterproof and penetration function of the coating.The presence of shrinkage holes reduces the sealing performance of the coating and makes it easier for water to enter and exit the coating.The permeability of paint is enhanced, and the penetration of water will eventually lead to the increase of ground humidity and indoor humidity, the breeding of mold, paint discoloration, foaming, shedding, alkalization and accelerated aging.
Three, the prevention and solution of shrinkage cavity
Prevention is the key to reducing coating shrinkage.The shrinkage rate can be reduced by designing reasonable and suitable coating production formula, controlling coating manufacturing technology and strictly controlling coating raw material testing.It has shrunk.It is usually difficult to solve completely and requires a combination of internal and external factors to control the degree of shrinkage.Can be selected by the better defoaming agent to prevent shrinkage, defoaming agent in the coating is well dispersed, dispersed after the defoaming agent particle size is appropriate, in order to reduce the existence of large droplet with low surface tension and different from the paint itself.There shall be no water droplets or oily substances on the construction ground.
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