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How to repair brick that’s flaking

The flaking bricks of letter writer Richard K. (Reader photo)

The bricks in the front of my home have been flaking off. This is a southwest-facing wall. Can you tell me why this is happening? Is there a way to repair the brick? What can I do to stop further flaking and damage? Was the wrong brick used to build my home? — Richard K., North Arlington, N.J.

I’m sorry to hear about this unfortunate news. Flaking brick more often than not is a cosmetic issue, but it’s serious because it affects the look of your home. The bad news is that there’s no easy way to repair and restore the brick.

The best way to explain what’s going on is to give a little background about brick. First and foremost, not all brick is the same, not by a long shot. The clay used as the raw material for brick is not the same. Different clays contain different minerals, and this affects the overall durability of the brick.

The manufacturing process also plays a part. When a brick is fired in a kiln, the elevated temperature in the kiln changes both the chemistry and mineralogy of the brick, making it harder. The time a brick is left in a kiln, where it is in the kiln and the temperature it’s exposed to all contribute to how hard the brick may be once it cools down.

Some varieties of brick contain minerals that are so durable that, if it is fired correctly, the brick becomes so hard it can be used as paving stones in roadways. The harshest environment for any brick would be to use it in the ground in a cold climate.

Visit Athens, Ohio, and you can see paving bricks in the downtown streets that have been there for well over 100 years and still look to be in perfect condition. That’s amazing when you think of the abuse the brick receives from truck and car traffic, as well as from bitter freezing temperatures over many a winter.

Water and cold temperatures are the enemy of brick. You have both where you live in New Jersey. What’s more, the front of your home faces southwest, and this is the prevailing direction from which weather hits your home. Wind-driven rain can and does penetrate some brick. If this happens and the temperature drops below freezing while the brick is saturated with water, the water expands as it freezes.

This expansion causes stress within the brick, which causes some of the clay to flake off. You can arrest and stop the flaking if you can stop water from entering the brick.

The best way to try to do this is to saturate the brick with a clear masonry water repellent that contains silanes and siloxanes. These sealers contain microscopic particles that fill the tiny voids in the brick that allow water to enter. You apply these sealers with an ordinary garden hand-pump sprayer.

To get maximum penetration of the sealer into the brick and the mortar joints, it’s best to have a helper. The helper will operate a backpack or handheld leaf blower. As you spray on the sealer, the helper blasts air at the brick to drive the sealer deep into the wall.

Be sure to buy a top-quality sealer and read the instructions. Some sealers require two coats for maximum protection. However, the second coat must be applied within just a few minutes of the first coat. If the first coat is allowed to cure and dry, it will block the second coat from entering the brick and mortar. Pay close attention to the sealer directions and don’t make the mistake of waiting too long between the applications.

It’s possible the wrong brick was used on your home. Your brick should have had a SW or SX grade. This acronym stands for “severe weathering.” About half of the United States requires this grade to be used because of the combination of cold weather and annual precipitation amounts. A large swath of the central and southern United States can get by with bricks that have a grade stamp of MW or MX, which refers to “moderate weathering.”

If you were to build a new home, you would want to ask about this when you visit the brickyard to select your brick. The brick should be clearly marked with a grade label in or on each cube.

If you have extra brick, and most people don’t, avoid the temptation to replace a flaking brick with a new one. You need to be an expert at getting the mortar to match should you attempt this feat.

Getting mortar to blend perfectly with your weathered mortar requires that you locate sand that matches the sand that was used by your original bricklayer. Not all sand is the same. Sand is simply tiny pieces of stone, and these particles come in different shapes, sizes and colors.

Once the cement paste in the mortar wears off, the sand creates the color you see in the mortar, for the most part. Not only must you get the sand right; you need to get the color of the mortar mix correct as well. It requires lots of testing to get a perfect mortar match.

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