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Brick Water Repellents

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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.


22 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?

  4. Does the brick wall have to be perfectly dry before using a repellent? Thanks
    If yes....is there a way to speed up drying.

  5. I have a 1930s house where the wall is solid wall and is coated with I think its plaster. I have filled in all the cracks I could see and used sandtex exterior white paint which has reduced the problem, but it there is still a patch of damp on the inside of the exterior wall. What do you suggest I do? Perhaps use an exterior water repellant, repoint and replace the bricks in question? then replaster? Or build a conservatory to protect the wall from rain?

  6. Hello,
    I have a brick fireplace in our living room that looks faded. I would like to apply some kind of sealant to darken it and bring it back to life. If you have suggestions of what to use I would very much appreciate it. Thank you,

  7. I live in a large Cond in the Chicago area that is brick and block construction that is 35 years old , we haven't had a lot of leaks , the board is getting a price to do tuck-pointing and using a water repellent called Protectosil Chem-Treat PB110,do you think it is necessary to preform a water absorption on the existing brick work , Thank you, Bob

  8. Hi Tim,

    We just had our building sealed today, and now it's pouring rain. The company said that it's not a problem because the sealant dries in about 30 minutes. Do you think that's accurate information? Unfortunately I don't know the brand or type of sealant used. We're paying ~$10,000 to have the building sealed, so I'm hoping that wasn't all for naught! Thanks in advance for your help!

  9. Hi Tim
    We've taken some soil out of the floor in the shed to convert into a living room but on the neighbours side there is 2 foot high soil against the wall.
    Is there anything we can use to protect the wall from the inside to stop damp coming through ?

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