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January 14 - January 18, 2019

What is the difference between a damp-surface tolerant and a wet-surface tolerant paint? How can we determine when a surface is damp or wet?

Selected Answers

From Warren Brand of Chicago Corrosion Group on January 25, 2019:
Yes. What Joao said, lol.

From JOAO AZEVEDO of Sherwin-Williams on January 25, 2019:
Interesting question and a good answer from Warren Brand. Tolerance to dampness involves the coating's curing mechanism, which should not be negatively affected by humidity saturation. A wet surface has a moving liquid film in the surface, as per Warren's proposed definition, and that poses challenges at the rheology level, too. The application method and the liquid film viscosity plays a role, both in the displacement of the liquid water film from the interface and in the ability to endure accumulation of more water at the film surface after application without washing the film. Thixotropic characteristics help: a coating that under mechanical stress (eg squeezed in the surface with a brush, or through airless spray) presents low viscosity and penetrates the profile well, displacing water, then dramatically increases the film viscosity once the stress is removed, "hanging" in the profile and resisting "washing." Fast curing helps here, too. Compatibility of the curing mechanism with the presence of water is always a must, of course, in both damp and wet situations.

From Warren Brand of Chicago Corrosion Group on January 24, 2019:
Ok. Since no one else is jumping into the pool (pun intended), I will. A damp surface is one in which there is no standing water. It is visually damp, or dark (concrete, CMUs). And, if one were to put their hand on it, the hand would come away mostly dry - certainly not dripping. A wet surface can be either entirely submerged, or have standing, or moving, water on it. To the best of my understanding, there is no difference in rheology or curing mechanisms of a material that can be applied to a damp or wet surface. The only issue is whether or not the material will stay cohesive when exposed to the substrate. For example, I have performed many underwater SCUBA repairs with various materials. Some materials will lose their cohesiveness and simply disintegrate underwater - thus not staying in a cohesive blob which is conducive to application. Others stay together, kind of like taffy, so that it can be manipulated (brushed, pressed, rolled) onto the substrate under water.

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Tagged categories: Asia Pacific; Coating Application; EMEA (Europe, Middle East and Africa); Latin America; North America; Surface-tolerant coatings

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