To Waterproof or Not Before Finishing Basement

c2harveyDecember 28, 2007

I live in Northern Virginia. My house is on a small hill with one basement wall (front wall) totally below grade, 2 side walls partially below grade,back wall totally above grade. The foundation is poured concrete. House was built in 1990. I have a sump pump and it appears to be operating properly.

When I removed existing builders insulation from walls, I found 2 vertical cracks in the foundation, one in the back wall and one in a side wall starting from the edge of a basement window. The side wall crack has oozed a small amount of water during recent heavy rains.

I am going to improve the grading around the house and put in some extended downspouts to get the water further away from the wall sides. In addition, I plan on sealing the cracks with poly injection foam.

I am debating whether to expend the effort to dampproof/waterproof the interior basement walls and floor since there appears to be a debate about effectiveness of such treatments. Other than the water periodically oozing through the crack in heavy rains, I don't have any wetspots on any of the foundation walls. Assuming that I can improve the drainage on the exterior, is it worth the effort to use a product like Dry Lok, RadonSeal or Sani-tred to waterproof the interior walls? If so, which product would be easiest to apply and most effective?

I also have both hairline and larger (1/16") settlement cracks in areas of the basement floor that have not let in any water (all are in the portion of the basement totally above grade)...should I seal the floor and those cracks also? If so, which product would be best?

At present my insulation plan for the basement is to glue XPS sheets on the concrete foundation, use metal studs to build the stud wall with fiber batts in between the studs. I am contemplating whether to use dry wall or Dens Armor Plus product to finish.

I'd really love to be able to use a product that allows you to remove the wall panels but haven't found one yet (would be nice if Owens Corning sold their basement finishing system to DIYers). If anyone knows of such a product, would love to hear about it.


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Built in 1990, I expect there's nothing on the exterior but a bit of cutback asphalt. So I would definitely look to interior protection. I can't comment on the products you mention. My preference is a crystalline waterproofing product.

A minimum of 1" XPS adhered to the interior walls is a Building Science preference. I've used this method in the past, followed by fibreglass batts and a metal framed wall. EPS is also acceptable.

But I find the following problems with this method: 1) adhering the boards to the walls can be very labour intensive on a poured wall. The irregularities in the wall may make it impossible to use adhesive. In fact, I've ended up using concrete screws and fender washers. With the boards not fully pressed onto the wall, you will get circulating air on the interior wall, which can lead to condensation, as can, the screws and washers. 2) metal framing creates a straight wall and is less messy than wood to build, but if the boards are not sealed properly, they will attract condensation.

If you are using this method, it's best to use shiplap boards or seal all the joints with building tape. And be sure to put the baseplate of your metal framing on at least a 1" thick strip of XPS to prevent wicking of moisture into the wall through vapour movement or liquid water.

Most recently, I've had basement walls and rim joists sprayed with closed cell foam equivalent to Code Minimum R12, then wood-framed. The clients can then choose to insulate between the studs or leave it open.

You can also use crystalline waterproofing on the basement floor. Though with no water in 17 years, that may be overdoing it.

    Bookmark   December 28, 2007 at 10:39AM
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I've read in a DIY framing book that you can experience "steel stud striping" when using steel-studs...essentially vertical stipes that appear on the covering drywall because the steel studs transfer heat/cold efficiently, making the drywall in contact with them cooler than the rest of the drywall and attracting dust that sticks to those cooler surface areas. Solution for that problem posed is to install rigid-foam insulation between the drywall and the metal stud.

Have you heard of this issue before? I assume if I can attach the XPS to my concrete foundation and seal all joints seems like this issue will go away...

You mention placing "1" thick strip of XPS under the metal base plate"...doesn't this XPS strip get crushed by the weight of the drywall once you hang it on the studs? Doesn't this result in a fair amount of tension on fasteners that attach the metal studs to the top plate as the XPS strip deforms?

Thanks for the input...

    Bookmark   December 28, 2007 at 11:20AM
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No "striping" problem on my own home over three winters. I have been using XPS under the baseplates since 1998. Again, no problems. XPS is even used under airport runways and highways.

The XPS prevents transference of cold and vapour. Also, as it raises the base it keeps liquid water from such things as burst pipes, stopped drains, even ordinary cleaning from reaching the wood, metal or drywall,

Here is a link that might be useful: XPS Product Overview

    Bookmark   December 28, 2007 at 1:12PM
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