Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

October, 2004

Paint Peeling Off Concrete

Q. Hurricane Isabelle knocked our Stadium Wall over in Septmber of 2003. We constructed a concrete block wall. After painting 2 coats of block filler, we painted the inside of the wall with an oil based sign paint, so we could put advertising signs on wall and it started peeling after 2-3 weeeks. We feel there was moisture still in the wall. In a concrete block wall, is it normal for moisture to penetrate from the bottom or top of the wall?

You don't tell me if the paint is peeling all way down to the block surface, or just off the block filler. I am going to assume that the paint is peeling all the way down to the block surface. You also don't mention how long after you constructed the wall, that you painted the surface.

Moisture can be migrating from behind the paint film and causing the paint to lift. You say you used a concrete block filler, is this material to be used as a moisture sealer also? Is the paint peeling off the block surface or off the mortar joints. Check to be certain that the proper materials were selected for the job.

You must remove all of the loose peeling paint from the surface of a block, sand the surface of the remaining paint and feather out the edges. Consider acid etching the surface with a mild muriatic acid solution prior to the application of any new coating. (BEWARE: Muriatic acid is similar to hydrochloric acid and is a hazardous chemical. Please read and before purchasing this chemical!)

After etching the concrete
thoroughyl flush the surfaces with clean water to remove any unreacted acid and then allow the surface plenty of time to dry. If you wait overnight after the acid etch, be certain to allow the concrete block time to dry from the morning dew.

Consult with your local paint supplier and explain your situation, ask for specific product recommendations for a block filler sealer, a product that will create a moisture barrier, one that you can apply a paint top coat over. Be certain to follow all the manufacturer's recommendations for dry times, application equipment, and procedures. Be sure to apply enough paint to cover the surface well, and provide the recommended dry film thickness in order for coating system to perform as required.

Please be aware that paints, coatings and solvents are chemicals and therefore you should always pay attention to proper handling procedures and be prepared to wear protective clothing, such as respirators, gloves, coveralls, etc. For further information on the health and safety requirements for the coatings and solvents you wish to use we strongly advised you to contact your local coating supplier. If possible, go the extra step and look for this information on the website of the product vendor.

Acid etching: You MUST insure that you are properly protected with goggles, acid-resistant gloves and proper clothing so that you don't injure yourself. For similar reasons, please insure that you keep others away from this process.


Jim Burke

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