Caulk Cracks at Inside Corners
Hairline cracks at inside corners usually signal slight movement between adjoining walls. Choose any type of latex caulk and cut the tip just short enough to leave a 1/8-in. hole in the end. Squeeze a narrow line of caulk directly over the crack. Then mold the wet caulk into the corner with a moistened finger. The caulk will remain flexible and keep the crack from reappearing. Avoid thick layers of caulk, which may look too rounded in a square corner.