Paints & Coatings Resource Center

Ask the Expert Question-and-Answer Archive

by Ron Joseph

March, 2005

Painting Concrete Block

Q. I have concrete block that we used in the construction of our office and shop building. We have not had much luck with the black paint we have used in the past. So what I would like to know is what type of paint do you recommend for painting concrete block?

A. There can be several reasons for the paints inability to adhere well to the concrete block. Most often concrete or cement will produce an efflorescence or alkaline salt that is deposited on the surface.

For the coating system to perform properly, these salts must be neutralized and removed to produce a good clean surface for the paint or coating to adhere to. This may be accomplished by using a high pressure power washer. In some instances the alkaline salts are neutralized with a mild acid solution such as Muriatic Acid. I don't recommend using an acid solution for an application such as this.

Investigate the availability of various types of concrete coatings from your local paint dealer. Explain your situation, ask for specific product and application recommendations. Be certain to discuss the needed prep work.

Remove all loose or flaking paint, I would think that you would have to remove most if not all of the existing paint from the surface of the block in order to create a good foundation in which to apply your coating to. Allow the block surface sufficient time to dry out after washing.

Ask the paint dealer about the use of a primer prior to applying the top coat paint. More often than not, a primer is necessary to ensure a good sound coating system that will last for several years.

When preparing any surface for the application of paints or coatings, be certain to take precautions to protect against breathing in any air borne dust particles or debris that may be created by the prep work.

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:

Proper handling and care must always be used when using any corrosive products. YOU MUST insure that you are properly protected with goggles, breathing protection, acid-resistant gloves and the proper clothing so that you don't injure yourself. Be certain to provide plenty of fresh air ventilation!

For similar reasons, please insure that you keep others away from this process, Especially children. Acid is always diluted before use.

The typical dilution for most applications is one part Muriatic Acid Slowly and Carefully added to ten parts water. Always add the acid to the water! Never add the water to the Acid! Gently stir the water while adding the acid. Be careful when mixing to avoid splashing the acid. Do not mix in a paper, ceramic, or metal bucket... use Acid resistant mixing containers such as glass or plastic.

We urge you to visit the web sites listed below for further information on the proper handling, use and disposal of Muriatic Acid.


Jim Burke

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