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Cinderblock - To paint or not to paint Answered

I always had this question in my mind.  Was the cinderblock designed to breathe?  In other words do we want the moisture to go from one side to the other in case of cinderblock walls (say in the basement walls?) 

Logically, I would think that the answer is that we want to prevent the moisture to go from one side to the other.  If that is the case, why the cinderblock makers do not make waterproof cinderblocks by adding water proofing chemicals during the manufacturing process?

I would greatly appreciate your insights on this subject.


I've seen sealant paint for interior of foundation, whether poured, or blocks.

I _think_ I've heard that if you paint the inside, water pressure might blow a hunk off. I think it's safer to excavate around the foundation, and paint the outside.

I never heard that a chunk of someone's basement wall will blow under hydrostatic pressure. The most dramatic thing in my experience is seepage. Instead of paint, contractors apply a synthetic membrane to the wall in order to waterproof.

I should emphasize that I THINK I heard that. So, it's a rumor, or maybe something I imagined hearing somewhere.

Ideally, you want a physical barrier for water and vapor on exterior foundation walls (usually a rubberized, tar-like product brushed on with a dimpled membrane that allows water to drain to a weeping system). Typical consumer "waterproofing" products don't work nearly as well, often don't offer any water vapor protection and break down over time ("waterproofing" in this case is more of a misnomer).

You also want to properly insulate between the cinderblock or concrete before adding drywall. This can be achieved with an application of spray foam, or with rigid foam insulation. The purpose is to create a "thermal break" between the two areas and prevent the formation of condensation. If you fail to insulate, the result can be a build up of moisture (and then mould) created when these two temperatures mix. People often think the moisture is from a leaking foundation, but its just simple condensation between the heated room and the cold foundation. Its exactly what happens when you take a cold drink outside on a hot day. You get condensation building up on the outside (the warmer side). Its not that your drink is leaking, its that there is nothing insulating the two temperatures from mixing. :-)

An efficient way to keep moisture out of your basement is a product called Drylock® masonry waterproofer. It comes in oil based and latex based formula and you apply that to the inside walls of your basement. I have used the oil based successfully. The more expensive alternative is to dig outside your foundation and waterproof the outside basement wall. The latter alternative has to be done by a contractor.

The number one benefit of a cinder block is cost - they are a cheap alternative to brick.

In the UK, they are used for internal walls and the inner layer of cavity walls - anywhere that weather-resistance (and waterproofness) are not so important.