Bleeding

• Stains that bleed through paint are particularly easy to handle, especially if they’re related to water or moisture problems or even from an unknown source. These issues will create streaks or dark spots on the surface of the wall, even through a new coat of paint. This is primarily due to using the wrong primer or too few coats of primer. If stains are present before painting, it is essential to thoroughly prime using a primer with a high hiding quality and allow it to dry completely before painting. An undercoat bleeding through new paint usually occurs when painting over a dark color. The cause is usually a moisture problem or because the undercoat is too bright to be covered by the new paint. Repair moisture problems and use a high-hiding primer.
  
  

Preparation

• There are three primary considerations when it comes to painting a block wall. The type of concrete block, the condition of the wall and the condition of existing paint will all influence how difficult a new coat of paint will be to apply. New, unpainted walls are unlikely to have serious bleeding issues. Walls with existing paint, whether in good or bad condition, will require at least a thorough coat or two of primer and sometimes a sealer to prevent bleeding of old paint or stains. A thorough cleaning with warm water will remove any surface stains or loose paint, while an acidic masonry cleaner is necessary to remove efflorescence, a white powder found on block that is the result of water permeation. If moisture is a problem, the source must be addressed before painting.
  
  

Priming and Block Styles

• There are two different types of blocks: smooth and split face. As the name suggests, smooth blocks feature a smooth surface that makes priming and painting significantly less time consuming. Split face blocks feature a rough texture that closely resembles stone. This uneven surface means split face blocks usually need double the amount of primer as smooth blocks. At least one coat of primer should be applied prior to paint; two or three are sometimes necessary if the block has been painted previously. In most cases, a coat of paintable waterproof sealer is recommended to keep paint from seeping through.
  
  

Selecting Paint

• The type of paint applied to a block wall is going to be key to preventing paint bleeding, particularly on existing block that has been painted. If old paint is peeling, it should be removed and the wall primed. If a previous layer of oil-based paint is present, it must be covered up with oil-based paints, as latex will flake off or peel. Use an alkaline resistant primer and a paint that is porous to prevent trapping water behind the paint. Latex is a good option in most areas, as are oil-based products. Spray paint will work in most situations, but it should be high quality and able to withstand local weather conditions.