Q&A / 

Brick Water Repellents

DEAR TIM: I have a problem with my brick veneer house. It develops leaks during wind driven rains. I can't seem to locate the source of the leaks. I purchased a brick sealer to solve my problem. I saw water repellents at the store, but the salesperson said they don't work as well. What do you think? B. N.

DEAR B. N.: Slow down! Do you still have the receipt for the sealer? You may need it. The sealer you purchased may actually harm your brick house. A water repellent may be a better choice.

The leaks you are experiencing are normal. Brick walls are by no means waterproof. Unfortunately, many homeowners think just the opposite. Bricks and mortar have a great capacity to absorb water. Both contain tiny passageways that actually suck water into the wall. Water can also enter through tiny cracks between the bricks and mortar.

Water leakage into older homes is rarely noticeable. These houses often were constructed using two or three layers of brick or block behind the face brick. As such, they can often absorb all of the rain water until such time as a storm passes. When the sun appears after the storm, the water is released back into the atmosphere through the tiny passageways. In your case, you only have one layer of brick. Once this layer has been breached, the water finds its way into your house.

This shine goes away completely once the silane / siloxane water repellent dries.

This shine goes away completely once the silane / siloxane water repellent dries.

Look again for cracks or small holes in the mortar. Pay particular attention to the small vertical (head) joints between each brick. This is the most likely place where water is entering. Rarely are these joints filled solid with mortar. The horizontal joints (bed) in your brick wall are usually filled solid and resist water penetration. If you find small holes or cracks, repair these before applying any coating.

There are two categories of clear brick coatings: film forming sealants and penetrating water repellents. Film forming sealants create a continuous barrier on the surface of the brick and mortar. They block the tiny passageways in the brick and mortar. Not only will they stop water from getting into the brick, but they also stop water from getting out. These compounds frequently contain acrylics, mineral waxes (paraffin), urethanes, and silicone resins.

Water repellents work in a different way. These products are designed to penetrate deeply into the brick and mortar. Some can reach as far as 3/8 inch into the surface. They coat the insides of the tiny passageways in the brick and mortar. However, the passageways remain open allowing the brick and mortar to breathe. These water repellents often contain silanes, siloxanes, or a blend of these chemicals.

The brick on the left have been coated. You can clearly see the wet edge.   Once the water repellent is applied and it dries, the brick look just like they did before you started.

The brick on the left have been coated. You can clearly see the wet edge. Once the water repellent is applied and it dries, the brick look just like they did before you started.

Film forming sealants can cloud and haze over. They can contribute to brick spalling (flaking) in colder climates. Water repellents rarely discolor brick. Because they soak into the brick and mortar, sunlight has a tough time breaking them down. Check the label on your product to see what chemicals it contains. If it is a film forming sealant, think long and hard before applying it to your brick.

SPONSORS / 

10 Responses to Brick Water Repellents

  1. I am planning to use brick for a backsplash in my kitchen and wish to seal it so i can keep it clean and it will not stain from coffee, red wine or other soil.

    What should I use to seal this brick?

    Thank you.

    • Pryce,

      You don't have to worry about stains when you have my Stain Solver. It gets rid of all the things you mentioned. If you make the mistake and SEAL the brick, the sealer can actually BLOCK cleaners getting to stains that seep past the sealer. Do NOT seal the brick.

  2. Tim,

    I need to get my repellent ordered and sprayed on my house before the upcoming hurricane season. Is there a particular brand you recommend?

  3. I have a 1930's semi that is rendered and painted. Do I need a sealant or a repellant?
    During recent building work inside the house the bulder removed internal plaster and said the walls were 'soaking' - and suggested I apply sealant externally. But do I want sealant or repellant?

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>