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Rodney R 08-12-2009 07:00 PM

Basement cement walls?
My house was built in the '50s. The orignal owner died and I bought it from relatives. My problem is this - the upstairs bathroom needs a complete overhaul, so I want to build one in the basement - it already has the toilet and the hot/cold water and drains. The real problem is the walls - they are a cement block, and they've been painted for sure twice, with what, I have no idea. I would like to cover the walls to hide the pipes, and make things look nice. HOWEVER, the toilet sits along one of these walls, and the tank is against one wall already, and only 4 inches from the other. My plumber said that a 10 inch toilet would buy me the room that I need on the backside, but I'm stuck with the 4 inch side clearance. That's OK. I had though about using some furring strips, and some greenboard, and some tileboard, BUT the entire basement are is damp. I am very concerned about getting mold behind the new walls. Nearly everybody that has seen the basement has the same concern. One guy suggested something called Ardex. I did a little research, and it says to apply on upainted surfaces, or remove all of the paint - I can't do that. Is there anything else that can be apllied, maybe over paint, or maybe if I rough the painted surface up a little???


Nestor_Kelebay 08-13-2009 12:11 AM

Rodney R:

It's important to know where the humidity in the basement is coming from. It could be coming through the walls, or through the concrete floor.

What I suggest you do is buy several "hygrometers" which measure relative humidity and can be bought from places like "Lee Valley" (for people making hobby weather stations) and hobby shops (for people making hobby weather stations). Tape the bottom and side edges of some clear plastic to your wall in several spots (especially those spots that have any mildew growing on them), drop the hygrometer in behind the plastic, and tape the top of the plastic to the wall. Do a similar thing on the concrete floor. The larger the piece of clear plastic you use, the more representative your results will be.

If water is migrating through the wall or floor, it will be trapped behind the plastic and cause the relative humidity of the air behind the plastic to increase.

Theoretically, you might want to toss a batt of fiberglass insulation over the hygrometers on the floor. That's because the relative humidity of air will change with it's temperature. The concrete slab is a thermal mass (it doesn't change temperature very quickly) but the air above the plastic can change pretty fast. You can get more accurate readings if you keep the air behind the plastic at a constant temperature, and that could be done to some degree by covering it with insulation.

If moisture is coming in through the walls, then coating the inside of the walls with some sort of impermeable coating COULD be the worst thing you could possibly do. The reason why is because such an impermeable coating won't stop the moisture from getting into the wall, it'll only stop it from getting out of the wall. And, of course, the result will be an increasing moisture content in the concrete wall. If water freezes where you live in winter, then you don't want wet concrete freezing. That's because the water expanding within the concrete as it freezes can cause something called "spalling" where the expanding water causes tremendous pressure inside the concrete, and "chips" will break off the surface of the concrete.

What I suspect is that you have a concrete block foundation, and ground water is penetrating into it and causing water to collect in the cores of the bottom row of concrete blocks. If the water is getting in through the walls, the RIGHT way to prevent that from happening is to excavate around the perimeter of the basement all around the house and water proof the foundation walls from the OUTSIDE. Sealing them on the inside is just hiding the problem.

Rodney R 08-14-2009 07:25 PM

OK, I see what you're saying. The right way to do things would be to drain all the water around the house.

I know that I won't get to that for sure this year. What if I would build my bathroom in that area and put some sort of paint on the walls? Something that would look decent, hide the joints and the fact that it's block, and maybe make some texture? Would anything like that buy a year or two? Would it be prone to cracking and falling off?


Nestor_Kelebay 08-14-2009 08:20 PM

If you just need something to tie you over until you can redo your upstairs bath, you might consider putting a shower and sink in the basement, and partitioning the "bathroom" off with just linen sheets or something. You can buy prebuilt shower units that you basically stand them in place and connect the hot, cold and drain lines to.

The problem is that you've got a damp basement and building walls in front of your concrete blocks and covering your concrete floor is NOT going to stop water from getting into your concrete walls and floor. I'd have the same concern... mold growth behind the walls.

Why not set up part of your basement as an emergency bathroom just as I describe, with a temporary shower, cheap bathroom vanity and leave the toilet just the way it is. Now start renovating your upstairs bathroom.

If I were you, I wouldn't start renovating your basement. I'd leave the walls and floors as exposed as possible. I'd hate to see you spend a pile of money and do a bunch of work only to have to pull it all apart later on because of the mildew and mold growing behind the walls and under the flooring.

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