Cause When paint is applied over a partially dried bead of caulk, the paint dries, first forming a film. As the caulk continues to dry, it separates from the underside of the paint film. Ultimately, the paint film cracks. Conditions that affect the drying time for caulks are air, surface or caulk temperatures below 40°F; high humidity; and joints in excess of 1/2" in width or depth.
Solution Surfaces to be sealed should be sound, dry, and free of oils, dust, mortar spatter, release agents, old caulk, bitumen, old paint or other contaminants. Remove flaky, loose and powdery material from the joint. Apply caulk only when temperature of surrounding air, surfaces to be caulked and caulk are all above 40°F. Do not apply when rain or freezing temperatures are expected. Joints should not be more than 1/2 in width or depth. Joints deeper that 1/2" should be filled within 1/2" of the surface with polyethylene rod or closed cell urethane foam. Fill the remaining joint with caulk, and tool within five minutes of application.
