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Old 06-25-2010, 04:55 PM  
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Default Best Basement waterproofing paint

Hi! I just bought a home with a partially finished basement and have noticed that the unfinished walls tend to sweat alot in higher humidity and heavy rains. I know this is fairly common, but, what is the best paint to buy to seal the walls and floor to stop this problem? Once I paint, I plan on getting a dehumidifier as well. I've read that drylok is good, and also Behr has one that is pretty good. Any thoughts? Thanks!!

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Old 06-26-2010, 12:45 AM  
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Any paint you apply to the INSIDE of the concrete is probably going to do more harm than good. The reason why is that the paint won't stop the moisture from getting into the concrete, it'll just stop it from getting out. The result will be a gradual increase in the moisture level inside the concrete until you get "spalling" of the concrete on the outside.

Spalling occurs when any wet masonary freezes. The water inside the porous masonary will expand with tremendous pressure as it freezes, and the masonary will break in the way it is least able to oppose that expansion force, and that is that "chips" of masonary will break off the front of the masonary, generally where the moisture content is highest.

This picture shows "spalled concrete". Only a small patch of concrete at the top of the picture is still smooth; the smooth surface has broken off the concrete in the rest of the picture. Also, this concrete has been cleaned up a lot before the picture was taken. Most often in spalled concrete you'll see broken and cracked stones in the concrete and areas where the expansion pressure pulverized the concrete into dust. This picture almost suggests that spalling does little harm to the concrete, but it does.

So, putting some kind of sealer on the inside of your concrete basement wall is as bad as some people putting a sealer on the exterior of their brick walls to prevent efflorescence from forming on the brick. That sealer doesn't stop the brick getting wet, it only prevents that water from getting out of the brick. The result is that moisture accumulates in the wall, and combined with freezing temperatures, the moisture will increase until you start to get spalling on the masonary.

If you want to waterproof your basement, there's no easy fix. You need to excavate around the outside of the house to expose the outside of the foundation walls and apply a water proofing membrane to the outside of your basement walls (similar to the ice and water shield they use on roofs. That will keep your basement walls dry, and dry warm concrete is happy concrete.

Also, you have to keep in mind that concrete walls have huge thermal inertia. It takes them longer to warm up than it does for the daily temperatures and humidity to change. So, if you have cold dry weather followed by warm humid weather, you're going to get condensation on the concrete walls no matter what paint is on those walls because they take a long time to warm up. So, nothing except insulation and a vapour barrier is going to stop condensation from occuring on the exposed concrete.

So, doing anything on the inside of a basement to stop water getting in just isn't the right approach. Moisture leaking through the walls should be stopped on the OUTSIDE. Products that you can use on the inside to stop moisture simply ignore the fact that using them could cause damage to the walls if the moisture continues to get into the walls and you live in a climate where temperatures drop below freezing in winter.

Last edited by Nestor_Kelebay; 06-26-2010 at 12:58 AM.
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Old 06-27-2010, 02:45 PM  
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Thanks for the advice!!
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