How to Fix a Flat Cement Roof

Inspect the roof when it is dry to locate the problem area. Look for obvious cracks or openings around the edges or in flashings. Look for evidence of past water pooling in low areas.

Clean off the roof with a scraper and/or pressure washer, so the surface is clear.

Cover up any noticeable openings or cracks with commercial-strength butyl seam tape for added leak protection, prior to applying your primer and sealants. Peel off the release liner on the tape and lay the tape over the cracks, running in the same direction. Press the tape down in the center first, then out toward the sides to form a seal. Test the tape on a small crack first to ensure it adheres properly. Use only one layer of tape for each crack.

Cover the roof with a coating of concrete primer using a long-handled roller. Pour the primer into a standard paint tray, then coat the roller and roll it over the surface of the roof. Use approximately 1/2 gallon of primer for each 100 square feet of space. Allow it to dry according to the manufacturer’s instructions.

Apply a base coat and topcoat of commercial sealant in the same fashion you applied the primer. Allow the base coat sealant to dry thoroughly for eight to 12 hours before applying subsequent coats. Apply 1 1/2 gallons of each sealant per 100 square feet of space for five years of protection, and 2 gallons per 100 square feet for 10 years of protection.