How to Waterproof a Painted Cinder Block Wall

Updated February 21, 2017

Painting surfaces such as wood, metal and concrete is typically a method of waterproofing, as paint fills the pores and helps to keep out moisture. Paint itself, however, is not waterproof. Prolonged and continuous exposure to moisture can cause discolouration, bubbling, peeling and flaking. Protect and prolong the life of painted breeze block by applying a clear waterproofing topcoat.

Choose a clear waterproofing topcoat that can be used over paint. Make sure the topcoat is also suitable for outdoor applications. If the wall was painted with oil- or solvent-based paint, do not use an acrylic, latex or water-based topcoat. If the wall was painted with acrylic, latex or water-based paint, you can use an oil- or solvent-based topcoat or an acrylic, latex or water-based topcoat.

Wash the painted surface thoroughly if the paint job is not new. Create a warm soapy solution, using approximately 1 tsp of dish soap per gallon of water, and wipe down the walls with a soft sponge. Rinse with fresh water, and allow the walls to dry.

Dilute the topcoat only if directed to do so in the manufacturer's instructions. Test the product in an inconspicuous area to ensure compatibility. If the paint changes colour or dissolves, you have chosen the wrong product. Topcoats may appear milky at first but dry clear.

Apply a thin coat of clear topcoat. Apply topcoat like paint, using a paintbrush, roller or sprayer. If you're using a solvent-based product, choose a paintbrush or roller with natural, solvent-resistant bristles or nap. Let the topcoat dry. Apply a second thin coat. In situations where water contact is frequent, add more coats.


If any part of the original paint job is compromised or damaged, do repairs such as sanding, priming and painting before applying the topcoat. If you find cracks in any breeze blocks, fill them with concrete-repair filler, using a putty knife.

Things You'll Need

  • Dish soap
  • Water
  • Sponge
  • Paintbrush, roller or paint sprayer
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About the Author

Mason Howard is an artist and writer in Minneapolis. Howard's work has been published in the "Creative Quarterly Journal of Art & Design" and "New American Paintings." He has also written for art exhibition catalogs and publications. Howard's recent writing includes covering popular culture, home improvement, cooking, health and fitness. He received his Master of Fine Arts from the University of Minnesota.