The ins and outs of painting masonry – advice from a Northern Virginia contractor.
What exactly does the term ‘masonry’ mean?
Masonry is a building material created from individual units arranged in a line and bound together by mortar, a sticky stone-based adhesive that is applied as a paste and dries as a solid unit. The units of masonry construction can be bricks, rocks, concrete blocks, or more exotic materials like glass, metal, or tile. Historically, the development of masonry allowed for a great deal of new versatility in construction, because masonry construction is both a highly durable and a highly flexible building technique. Brick and stone walls, patios, chimneys, fireplaces, and archways are all examples of common ways that masonry enriches our built environment.
While many people enjoy the natural look of masonry, particularly brick and stone, there are many practical and aesthetic reasons that masonry ought to be coated.
From a practical standpoint, masonry shares the same enemies as just about every building material: moisture and organic decay. Brick, concrete, and mortar are all vulnerable to physical damage when exposed to moisture, especially if the moisture is subject to temperature changes (such as the typical exterior freeze-thaw cycle in the DC area). The porosity of these materials also allows them to conduct moisture to even more rot-vulnerable building materials which may lie adjacent to them, like wood and drywall. Mortar can itself become food for mildew and other organic contaminants if the proper protections are not in place, and the mortar is exposed to sufficient moisture.
From an aesthetic standpoint, while masonry can be quite beautiful on its own, it can be difficult to harmonize with your desired color scheme. The reds and browns of brick, or the cool grays and blues of stone, may not match the colors you want for your siding and trim, and limiting your choices to those that match the “given colors” of your masonry may constrict your creativity.
For all of these reasons, many people choose to paint their masonry. Painting a brick or stone exterior wall can look very beautiful, and painting a concrete block basement is essential to protect the masonry (and even the basement!) from water damage.
Here are some things to keep in mind:
1. The mortar in masonry (as well as the concrete itself, in the case of concrete blocks) contains lime, which is highly alkaline. It takes the masonry about a year to fully cure; until then, the lime is in the process of reacting with the carbon dioxide in the air. Painting too soon, or using a type of paint unsuitable for masonry, will cause the paint to deteriorate due to alkaline exposure. It is ideal to wait at least a month before painting fresh masonry, and to use both a latex masonry primer or other alkali resistant sealer, as well as a layer of 100% acrylic latex masonry paint. Read the labels; if the product is not specifically engineered for use on masonry, it will not perform up to industry standards.
2. If you are working with a chimney, do not use any sealers that are not vapor permeable on the inside of the chimney. There are specific products formulated for waterproofing chimneys (which can degrade very quickly with no protection), which are vapor permeable. Painting the masonry on the fireplace on the interior of a home will not cause the same problems.