EXTERIORS : Painted Masonry’s Past Is Written in the Stone

Stone and brick on the outside of a house lend a charm all their own. And while some prefer the natural look, others go for painting their masonry. One problem to be aware of is that, once masonry is painted, it is difficult to restore to its original condition.

There will always be particles of paint left in the texture of the brickwork, and even smooth stone, which can be stripped successfully, may be stained by paint.

When it comes to cleaning old brick and masonry in preparation for finishing a wall or leaving it natural, first brush off all loose debris with a stiff-bristled brush.

Don’t use a wire brush unless the masonry is badly soiled, because the wire brush may leave scratch marks. Remove dirt and dust by washing the surface.

Scrub heavy deposits with a half-cup of ammonia added to a bucket of water. Abrade small cement stains or other marks from brickwork with a piece of similar-colored brick, or scrub the area with a household cleanser.

New brickwork or stonework should be left for about three months until it is completely dry before any further treatment is considered.

White powdery deposits called efflorescence may come to the surface over this period. These are soluble salts within the building materials that gradually migrate to the surface as a wall dries. The same condition can occur on old masonry if it is subjected to more than average moisture.

Efflorescence itself is not harmful, but the source of moisture causing it must be identified and cured if the surface is to remain unstained.

Regularly brush the deposit from the wall with a dry, stiff-bristled brush until the crystals cease to form. Don’t attempt to wash off the crystals, because they’ll merely dissolve and soak back into the wall. Above all, don’t attempt to paint a wall that is still efflorescing, and therefore damp.

When the wall is completely dry, paint the surface with an alkali-resistant primer to neutralize the effect of the crystals before you paint with oil paint. Water-thinned paints or clear sealants let the wall breathe and so are not affected by the alkali content of the masonry. Most exterior latex paints can be used without primer.

Mold growth on masonry is another problem you may have to deal with. Molds and lichen will flourish only in damp conditions, so try to cure the source of the problem before treating the growth.

If one side of the house always faces away from the sun, it will have little chance to dry. Relieve the situation by cutting back overhanging trees or shrubs to increase ventilation to the wall. Make sure the earth surrounding masonry is graded so surface water flows away from it.

To remove growth, brush the wall with a stiff-bristled brush. Microscopic spores will remain even after brushing. You’ll have to kill these with a solution of one part household bleach in four parts of water. Paint on the solution and let it sit for 48 hours before washing it off. A second application may be necessary.

If this doesn’t do the trick, use a fungicide available at home centers. Apply the fungicide and let it sit for 24 hours before washing it off with water.