Can you waterproof a basement and install a floor without using as many scary chemicals as everybody else?


Can you waterproof a basement and install a floor without using as many scary chemicals as everybody else?

Asked by HelenJay

Not sure if the walls or floor get damp or wet. Want to install a laminate or other floor in a basement. Maybe walls, sheetrock or woodpanel. Not sure looking for most natural way to go. Trying to stay true green.

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Joel Hirshberg's picture

Dear HelenJay,

The quick answer is yes. There are some excellent non-toxic sealers that prevent moisture penetration in concrete walls and floors.

If your basement is wet, it's usually coming from:

  • moisture underneath the slab or from
  • water running through cracks in the walls.
  • It may also be due to condensation if your basement is cold and the air is warm, as it is this time of year.

Using a sealer can help block moisture penetration to a degree, but it can't stop Mother Nature completely. Hydrostatic pressure builds up when the water table rises underneath your concrete slab. It's near impossible to stop this 100%. This results from excessive rain, drainage pipes that are old and plugged up, or gutters that are not well connected that allow rain water to run back towards the foundation.

Try to stop the water at its source

It's a good idea to consult with an excavation contractor who can examine your basement to determine where the water is coming from in the first place and try to stop it at its source or divert it.

This can be pricey, but sometimes it's just a matter of changing the slope of the ground away from the house. If the drain lines around your home are plugged up, this can require serious work, but ultimately, well worth it.

Topical and penetrating sealers

Using a sealer can be helpful if you choose the right type for your application.

Most sealers for concrete are topical, which means they sit on the surface and block moisture from the top down. This makes cleanup easy, but they eventually wear off through normal wear and tear and continual cleaning. Topical sealers won't stop water coming up from below or from the side walls.

Penetrating sealers, on the other hand, work better at this because they go deep inside and seal from within. However, many contain nasty solvents which can off-gas for months or years. Water-based penetrating sealers work well, but some still contain toxic ingredients, so you have to do your homework.

Our favorite is GBS Penetrating Sealerwhich penetrates 2-5 inches into the concrete and chemically bonds to the substrate, becoming one with it. (In the name of transparency, GBS Penetrating Sealer is a private labeled brand of sealer offered exclusively through my company Green Building Supply.)

  • It's completely non-toxic and has no odor; and it stops water that comes in from the floor or the walls.
  • It can block hydrostatic pressure by 50% which is better than most.

Like all penetrating sealers, it can only be applied when the concrete is fully dried and, if new, it must be fully cured. The concrete must also be clean and cannot have any topical sealer on it or GBS Penetrating Sealer won't penetrate through it. And the pH must be neutral 7-9. This is not a problem for concrete a year old or more, but it can be for fresh concrete that has a very high pH level.

Vapor barriers are usually required

Sealing concrete is an insurance policy for your flooring but it does not take the place of solving the larger problem of water penetration.

Most floating floor manufacturers require vapor barriers such as 6ml plastic for warranty purposes, but penetrating sealers add one more level of protection. It's a smart and inexpensive way to help protect your investment.

You may also wish to use a sealant for any small or large cracks. Try our M-1 by Chemlink. It's non-toxic, virtually no odor and seals well in damp places.

If you have further questions, please email me

For more information:

Read "How do you fill and seal cracks in concrete building blocks? How would I seal the entire inner basement wall against moisture from outside?" a Q&A answered by Harold Remlinger.