Thorough preparation is crucial before you paint masonry. Learn how to prepare masonry and paint masonry to ensure you get a perfect finish.
Other than a quick wash and sanding to remove grease and dirt, interior masonry usually does not require much preparation before painting.
Exterior masonry is a different story. The extremes of heat and cold will have damaged the old exterior paintwork, leading to dusty, chalky, flaky surfaces that must be thoroughly prepared before you paint masonry. Proper preparation is vital and failure to observe this step could ruin the final paint finish after you have redecorated.
How to Prepare and Paint Masonry: Curing a Dusty Surface
If the old paint rubs off as a dusty or chalky deposit you will need to treat the wall before you redecorate. Brush the surface with a stiff-bristle brush and then paint the entire wall with a stabilizing primer. This will cure the dusty surface so that fresh coats of paint will stick to it.
Clean splashes of the stabilizer from surrounding woodwork. For very dusty, chalky walls, you may need to apply an additional coat of primer. Select a white primer that will serve as an undercoat as well as a stabilizer.
Dealing With Flaky Paintwork Before You Paint Masonry
Flaky paintwork is very often a sign that the surface was not prepared properly before it was last redecorated. Don’t make the same mistake again. Damp walls can also lead to flaking paint, so correct the damp problem and let the wall dry out before you paint masonry.
Use a paint scraper and a stiff brush to clean off all flaky paintwork and loose material and debris. Finish the flaky paint removal with a coarse, heavy-duty sandpaper.
Paint the entire masonry wall with a stabilizing primer. Again, choose a white-colored primer that can serve as an undercoat as well as a stabilizer.
If the flaking is caused by spalled brickwork, correct this problem by applying a bitumen base coat to the spalled areas.
After removing all the flaky paintwork and stabilizing the wall, apply two coats of reinforced masonry paint.
Treating Stains Before You Paint Masonry
Sometimes painted brickwork chimney stacks will show ugly brown stains, outlining the various courses of the brickwork underneath. This is usually because the pargeting, or internal rendering, has failed. This permits tarry, sooty deposits to build up and leach through the mortar to the outer paintwork.
Correct the problem of chimney staining by fitting a flue liner inside the chimney. Treat the brown stains with an aluminum spirit sealant before applying two coats of fresh exterior masonry paint.