For Your Home CMU Building

Paint a CMU Building

Project Scenario

Polly, a property manager has on old cinderblock building downtown that she would like to get painted and address a water issue coming through the walls.


  • Pressure wash all bare block surfaces until all dirt and efflorescense are removed.
  • Pressure wash painted surface of building and remove as much peeling paint as possible.
  • Use mildew retardant solution if necessary. Rinse and let dry thoroughly.
  • Hand scrape painted wall until no more paint will come off.
  • Patch all cracks that are more than 1/16 inch with knife grade elastomeric caulking.
  • Caulk all windows, doors, and joins.
  • Check walls for moisture before coating. Determine and correct the source of moisture before painting.
Paint CMU Cinder Block Building

Primer Coat

If mortar contains hairline cracks, use 501901x Masonry Block Filler.

Best:      501901x Block Filler Good:    501601x First Coat Primer

Top Coat

Best:     51130xx Super Reflex Elastomeric
Better:  51230xx pHlex-tite Elastomeric
Good:   52110xx AC-909 Satin

Caution! Things to consider

  • Metal flashing should extend 6 inches from the roof cap and be snug against the building. Paint top section of wall before re-installation.
  • Caulk the cap with Dap Dynaflex 230 caulking to make sure no water can get underneath and into the wall.
  • Keep in mind that for every 10 mph that rain is driven into a wall, it can climb 1 inch. A 30 mph wind can drive rain 3 inches under a cap.
  • When using heavy bodies materials, make sure you use a pump big enough to move the material. Use a large diameter hose and remove all your pump filters and gun filters before you begin.
  • For waterproofing, a "pin-hole" free film is crucial.
  • Check coverage rates and dry film thickness requirements carefully.
  • Textured elastomeric is available.
  • Correct mortar issues with Rockite.

For more information about this or other painting tips & techniques, our paint & coatings products, or general DIY paint and coatings questions, please contact us online or by calling 1-800-452-2315.