It is advised that unpainted masonry be left unpainted as it can trap moisture and can potentially cause deterioration of the brick. As water freezes it expands, which can cause stress cracks and spalling in the brick, and ultimately failure. Painted brick can also lead to condensation and mold issues on the interior of the building. In unpainted brick buildings, the porous brick absorbs water and allows the water to evaporate, leaving the brick intact even with years of exposure.
Once a building is already painted, it is the owner’s choice to repaint it or consider paint removal. While there are many success cases, paint removal is not always successful and can also cause damage to the building so it may be better to leave the brick painted.
When removing paint, use the gentlest means possible. A test patch in a small, discreet location should be conducted first before cleaning is undertaken to verify that it will not damage the brick underneath. To remove the paint completely, the brick should first be cleaned with a soft bristle brush and water. If that is not sufficient, then power washing with a mild detergent or chemical cleaning can be considered. Power washing should not exceed 300 PSI because higher pressure could damage the hard exterior of the brick. If the hard exterior surface is damaged, the softer interior of the brick is left exposed and vulnerable to deterioration. For this reason, brick should never be sandblasted.
The following National Park Service Preservation Brief and General Service Administration Technical Procedures provide guidance on how to clean brick: