How to Seal a Brick Chimney From Water and Rain

December 4, 2012

A brick chimney can cause leaks into the interior of a home in several ways. One of the most common is water from rains being absorbed into the brick and then showing up on the interior. Brick and mortar are naturally porous materials. They soak up a great deal of water, especially when driven by hard winds. It is possible for this water to then migrate to a home's interior and cause damage to the drywall and framing. Also, water can be trapped inside the brick and mortar and then freeze. When the water freezes, it expands as ice and can break down the mortar and brick.

To stop this water, a good brick chimney sealer is needed. Look for a water repellent that is made up of a silane/siloxane material. These water repellents seal the brick from water. And they are 100% breathable. This means that any water vapor from the interior of the chimney or home will escape and not be trapped inside. Finally, these water repellents do not change the appearance of the brick.

Step 1. Make sure the mortar joints are in good shape. If they are cracked, loosely bonded or crumbling, they will need to be tuck pointed. This is where the old mortar is repaired with new mortar.

Step 2. Remove any dirt or loose debris from the brick and mortar. This will allow the sealer to completely be absorbed.

Step 4. Apply the silane/siloxane sealer with a brush, roller or sprayer. Typical application rates are 100-150 sq. ft./gallon. The application should not allowing ponding on the surface of the brick.

Step 5. Allow the product 24 hours to dry without rainfall or temperatures below freezing.

After 3-5 days the brick and mortar will become water repellent. Water from driven rains will not be absorbed into the brick. The mortar and brick of the chimney will have a longer life because water will not freeze and expand inside them.


A-Tech Chimney Sealer can be purchased here.


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