Garage concrete slab sweating

[jfh230]

It sounds like a vapor barrier problem. Typically when pouring a concrete slab you put down 4" stone over the compacted dirt, then a layer of poly vapor barrier and then pour the concrete. The stone base helps with draining away any underground moisture and the vapor barrier prevents the moisture from reaching the slab. If you don't use at least 6 mil poly then the poly will get destroyed with holes when pouring the slab. Holes in the poly allow the moisture thru.

A quick check is seal down a two foot section of the slab with plastic being careful to fully tape all edges securly. Come back in 24 hours. Moisture on the top of the plastic is condensation, moisture under the plastic is vapor barrier problems.

If you have a vapor barrier problem most sealers will not help and will make any future attempts at fixing more difficult because you will have to remove the sealer (sandblasting or shotblasting). The only product I have had any type of success with in fixing vapor barrier problems is hydraloc. Its not so much a sealer as a penetrant which soaks into the concrete and fills up all the little voids. If I remember it will go down a couple of inches into the concrete. As it cures it turns solid and becomes a permanent part of the concrete. I've had some sucess with this in older basement slabs that I know don't have a vapor barrier.

The company is enduroseal www.concretesealer.com

I think it was about $150/5 gal pail. You buy it direct from manufacturer. Keep in mind that when dealing with a vapor barrier problem the only 100% solution is to rip up the slab and install it again. Nothing you put on top is going to work 100%.

Good luck
Jack

 

[DaveNay]

</font><font color="blue" class="small">( A quick check is seal down a two foot section of the slab with plastic being careful to fully tape all edges securly. Come back in 24 hours. Moisture on the top of the plastic is condensation, moisture under the plastic is vapor barrier problems.)</font>

Hey, that is an excellent method! I never thought of that....nice and simple! /forums/images/graemlins/wink.gif

Dave

 

[flyer]

Thanks Jack. Great idea on determining the problem! I will try that over the next day or so. I don't know how the slab was originally constructed, and of course I would like to do anything short of tearing it up and re-doing.

 

[Junkman]

another quick check is to lift a box or can that has been sitting on the floor for a few days, or months in my case. If it is wet underneath, then it is coming from underneath. If dry, then from above...... If you have a neat garage, then this probably won't help..... /forums/images/graemlins/grin.gif

 

[DaveNay]

</font><font color="blue" class="small">( another quick check is to lift a box or can that has been sitting on the floor for a few days, or months in my case. If it is wet underneath, then it is coming from underneath. If dry, then from above...... If you have a neat garage, then this probably won't help..... /forums/images/graemlins/grin.gif )</font>

....or coming from something inside the box that is now leaking. /forums/images/graemlins/tongue.gif

Dave

 

[Egon]

After finding out where the water is comming from you may be able to install a little sump that gets pumped out.

Think I'd stay away from a sealer if the water is comong from below.

Drainage trench ending in sump outside may also be a solution. Probably work the best .

Then again maybe you are working the slab too hard and its just natural sweat!!!

/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

Egon

 

[johnday]

jfh20; Right you are, up here we try to use clean sand in place of gravel, using that minimizes even more the chance of not puncturing the visqueen. BTW, the trick of laying a piece of plastic on the floor also works for basement walls. I remembered that all by myself once you jogged my mamory. /forums/images/graemlins/cool.gif

 

[engineer]

A product that I have used to seal manholes and pump stations both old and new is Aquron 2000, see the following address: http://www.aquron.com/products/aqu2000.htm

Have had quitre good success with the product. It will soak in to the concrete similar to a wood preservative on pine, this is where the similarity ends. The Aquron 2000 will bond the free water remaining in the concrete (even after 14yrs.) essentially creating a pseudo-crystline gel thus sealing the concrete. The surface of the slab will remain unchanged.

If moisture truely is seeping through the concrete an epoxy type surface finish could cause the moisture to build up in the concrete and potentially cause the epoxy finish to spawl.

engineer