Mud cracking, is a phenomenon that occurs when a flat latex paint is used over a glossy or soft paint or material (like caulk). There are other reason for mud cracking but in the case of caulk, it is usually the result of using a flat paint directly over the caulk. This usually occurs with highly pigmented interio rlatex flat paints, usually it doesn’t happen with oil paints or more flexible exteior latex flat or other sheen paints.
Solutions:
- Prime over the caulk before painting Use an appropriate oil based primer over the surface, or over the caulking compound after it is suitably dry for paint. A good primer for this is Zinsser’s Coverstain or XIM 400 white. Use these primers with good ventilation during and after priming. Once the primer is dry, you can paint with any latex paint.
- Use an oil based paint instead of a latex paint. Oil based paints are not likely to crack when applied directly over caulk.
- Switch to a non-flat paint. Normally, a satin or semi gloss paint will not crack over caulk because of the added resin content in the paint.
Good caulk painting practice
Use a paintable caulk and allow it to dry according to the label before painting it. If you are going to use a flat interior latex paint over caulk, you may have to prime first before painting. Exterior paints will not likely crack over caulk since they are more flexible.
Related Articles: Kilz, Coverstain & Xim 400 Primers
Is the paint compatible with the caulk?
You can get cracking if the paint is “crawling” on a silicone or other caulk that is repelling a latex paint. Always use a paintable caulk. Acrylic latex caulks or paintable silicone modified acrylic caulks work well with most paints. Make sure the caulk is dry before painting.
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Why is my paint cracking over caulking?
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