Q&A / 

Concrete Vapor Barrier Video

Hi, I'm Tim Carter from AsktheBuilder.com and I am here on the job site today. It is real pretty cool as they are getting ready to pour a concrete garage slab in just a minute.

But first I want to show you one part of the slab that is really important and it is something you might forget if you are doing some concrete work. Look at this. What you are seeing is a big black sheet of plastic. This goes underneath the entire slab, it's thin and it goes everywhere. The purpose of this vapor barrier is simple. It stops the water vapor from the soil from coming up through the concrete. It might be hard to believe but water vapor goes right through the concrete and it will make the inside of the garage damp if you don't have it.

Make sure you have a good vapor barrier under your concrete slabs.


One Response to Concrete Vapor Barrier Video

  1. Dear Mr. Carter,

    For our outdoor hot tub the contractor excavated and installed 10" of compacted 411 berm stone mix, then poured a 8" thick concrete pad with wire mesh to support a 7-1/2 ft. x 8-1/2 ft. 500 gallon hot tub.

    He forgot the vapor barrier.

    Is this going to cause water vapor problems? The not yet installed hot tub has a treated wood base.

    We are considering having a 10" high treated wood frame on top of the concrete pad to allow some air movement over the concrete pad and so the hot tub's interior step is on the same plane as the existing deck that is adjacent to the hot tub for safer entry/exit.

    Is the missing vapor barrier going to ruin the whole project? Is there anything we can do?

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