How to Paint a CMU Basement Wall

Make sure your CMU wall is sound before you paint.

Nothing spruces up an unfinished concrete masonry unit (CMU) basement wall like a coat of paint. But before you paint your CMU, make sure that the wall is sound. A coat of paint on a damaged wall can trap moisture escaping from the surface and ruin the paint job in short order. Your CMU basement wall must be sealed and impervious to moisture before you paint. If the walls are damp and moldy or you notice popped out blocks, cracks or any other damage, contact your contractor before proceeding. The wall may need repairs or a coat of sealant before you proceed.

Things You'll Need

• Trisodium phosphate (TSP)
• Bleach
• Laundry detergent
• Bucket
• Scrub brush
• Painter's tape
• Plastic sheeting
• Masonry primer
• Masonry paint
• Paint tray
• Long-handle paint roller

Instructions

1. Mix 3 ounces of TSP, 1 ounce of laundry detergent, 1 quart of bleach and 3 quarts of warm water in a bucket. Scrub the walls with the solution, using a brush, to remove all surface debris. Sponge the wall down with a bucket of fresh water to remove all of the TSP solution. Allow the wall to dry for 48 hours using a fan and an open window in the room.

2. Apply painter's tape to the floor and ceiling and on the outer edge of any fixtures attached to the wall. Cover the floor with plastic sheeting to catch any drips.

3. Mix the masonry primer well and pour it into a paint tray. Paint the wall with one thin primer coat via a long-handled paint roller. Always lead with a wet edge. Spread the paint onto unpainted wall sections, then back onto painted sections with horizontal or vertical strokes.

4. Allow the primer to dry for the label-recommended amount of time (usually 12 hours) before applying the topcoat.

5. Apply the topcoat following the directions for the primer coat. If desired or dictated by the paint's label, you may add another coat after the appropriate drying time has elapsed.

Tips & Warnings

• Masonry paints and primers are labeled as such and available at most hardware and home improvement stores. This viscous paint is designed to fill the many pores of CMU blocks and facilitate a professional-looking coat. Masonry paints and primers are available in alkyd and latex formulations. Both are suitable for CMU walls as long as you use alkyd topcoats on alkyd primers and latex topcoats on latex primers. Do not mix alkyd and latex paints. When presented with a selection of masonry paints from different manufacturer's, let price be your guide. More expensive brands are often of higher quality and provide a smooth, long-lasting coat.

References

• Rodda Paint: Paint a CMU Building
• Emery County Senior Center – Green River: Painting
• Masonry Works Tools: Painting Brick Masonry