Some people install brick veneer without flashings, thinking they can always fall back on the application of a coating if they have a water penetration problem. However, most coatings can’t bridge bond breaks or hairline cracks. If you use a coating on bricks, remember that you are taking a chance that the coating won’t work.
While clear coatings sometimes prevent moisture entry, coatings can also create problems. If the pores of the masonry are coated, and water gets into the brick from the back side, where the bricks aren’t coated, then the water can’t get out. When the saturated bricks freeze, the expansion of trapped moisture within the brick can cause severe deterioration.
Some coatings are breathable, which means that the coating allows moisture to exit the wall as vapor. But remember — if a coating is applied, the pore structure of the brick has been altered. The pore structure directly affects the durability of the brick. There must be enough pore space in the brick to allow any absorbed moisture to freeze and expand. If the pore structure is altered and the room for expansion is no longer available, the brick may deteriorate.
If you decide to try a coating, choose a breathable coating. While some types of silanes and siloxanes have proven to reduce moisture penetration without reducing the durability of the masonry, siloxanes appear to be more successful with brick.
Siloxanes are fairly expensive, but you get what you pay for when it comes to coatings. If it costs $5 a can, you can do without it. In any case, properly installed brickwork should not require coatings to prevent moisture penetration. —J.C.
