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To prevent rot and mold behind your home’s brick walls, make sure the weep holes are not blocked

The hole where the brick meets the concrete patio surface serves a very important purpose and should never be filled. (Todd Joerger)

I live in a brick townhouse. In the back, there is a patio door leading to a concrete deck. The patio door sits on top of some brickwork. I’m trying to make sure the patio door is all sealed up, keeping out any and all moisture. I’ve noticed what seem to be round weep holes along the very bottom of the brickwork. I would like to plug them with some mortar to keep the moisture level down. Will this do any harm? What purpose do the weep holes serve? — Todd J., Newport News, Va.

Whatever you do, do not fill those weep holes. They’re an integral part of the drainage system to keep water from building up behind the brick. If allowed to contact any untreated lumber, this water will cause serious wood rot, mold and, eventually, structural problems with your home.

Allow me to explain the dynamics of brick walls, brick veneer and rain, and you’ll be able to do a fantastic job of protecting everything behind the brick.

Brick walls leak water. They have always leaked water. Builders and masons from hundreds of years ago knew this and developed a set of best practices to ensure that their brick buildings did not fall apart.

Sadly, for years, lots of this information was handed down by word of mouth. To add insult to injury, not all brick masons today are required to learn all the history about brick construction. If they had a better understanding of what’s going on, they’d be able to do a better job of preventing water infiltration.

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Most water enters brick walls along the interface where the mortar touches the brick. You may not see the ultra-fine line or pathway, but it exists. On rowlock brick, like you see under your door threshold, the problem is even more severe because the mortar joints are facing the sky. Rainfall has no problems getting into a brick wall at these locations.

Think about what happens in a storm, when rain is lashing against the side of a brick wall. The pressure of the wind is forcing the water into the brick wall through the cracks, like you’d pound a nail into a piece of wood. Each successive raindrop that hits the wall pushes against the water that just hit seconds ago. This, in combination with the wind pressure, allows water to stream into the wall. This water needs to be captured and redirected so it doesn’t come in contact with any of the wood framing in a brick veneer house.

Years ago, in solid masonry buildings, the masons and builders dealt with this water in a different way. They used harder brick to construct the outer face of the walls, but the brick used for the inner second or third course was a softer brick that readily absorbed water. You can usually spot these bricks because they’re an orange color, not a deep earth-tone color.

These soft bricks would absorb the water from the storm, and the next day they’d send the water back out to the air via capillary attraction and vapor pressure. As the sun beat on the wall and the breeze blew over it after the storm, the water stored inside the inner brick would come out faster than rats abandoning a sinking ship.

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In modern brick-veneer construction, it’s imperative that this water be captured by flashings and waterproof membranes and then redirected to the exterior of the brick wall. Parts of this system are the round weep holes you see at the bottom of your brick.

All sorts of products are available to channel the water back to the outside of a brick wall, but it’s impossible to retrofit them into an existing brick veneer wall.

Your best bet to protect your home is to apply a clear silane/siloxane water repellent that has enough solids in it to help plug the tiny cracks that allow  water to enter at the brick/mortar interface.

When spraying these products on a brick wall, it really helps to have an assistant to operate a backpack leaf blower. This person directs the airflow to the area being sprayed with the sealer. The high wind pressure created by the blower forces the water repellent deep into the brick wall to help create a strong barrier against water infiltration.

If you’re building a new home with brick veneer, you’ll want to read many of the technical notes from the Brick Institute of America. These are easy to understand and have great illustrations. They show all the places where you need very important flashings to collect the water.

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One of the places flashings are a must is under rowlock brick, as you have in the photo you sent. The sad thing is that many of the brick houses I’ve inspected lack this flashing.

It’s also important to make sure the pathway from behind the wall to the front of the weep holes is wide open. All too often, mortar falls behind the back of the brick veneer and makes it very hard for water to easily enter the weep holes. There are products and methods to ensure that this doesn’t happen, but many bricklayers and builders don’t use the products — and then problems happen as the house is subjected to pounding rain.

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