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Excessive Moisture Concrete Slab Sealing

Posted by florida_wen (My Page) on
Fri, Mar 16, 07 at 10:38

We live in Florida about 25 miles East of Tampa. Our development is about 20 years old, as is our house. Our house is built on a concrete slab, just as most Florida homes. Im not sure if 20 years ago code required a moisture barrier to be installed between the earth and the slab but even if they did, Im sure it has disintegrated and cracked by now. We are in the process of removing the original carpet and backing (used in EVERY room of this house) and replacing most areas with ceramic tile, but there are two or three rooms we "would LIKE" to install "laminate" flooring. What we have noticed since we moved here about six months ago, is that when you place an object directly onto the carpet, lets say for example a plastic (Rubbermaid) tub with a little weight in it, and leave it there for three or four days, when lifted we find "moisture" and small water droplets on the bottom as well as the carpet being moist. Obviously the same "test" can be done with a piece of plywood placed onto the carpet with a brick on it. We are fully aware that concrete "breathes" and especially with our very, very moist soil here in this development SOME "dampness" would be normal, but we are afraid that ours might be excessive. We were told that we should have an "expert" come out (for ~$150) and do a "moisture test". I know from reading a brand name laminate manufacturers web site that down in the South where we live the "average" moisture content is 11%, the highest in the USA, and the maximum recommended is 14% for any laminate or wood floor. Obviously the results of our "moisture test" will determine what OUR "moisture content" is. I am fully aware of installing a first layer of 6-mil. non-recycled (100% virgin) resin polyethylene film as a moisture barrier, over lapping ALL the seams at 8", then installing the" sound deadening foam" OVER that (taping the seams) and then the laminate flooring. What I am wondering is WHY CANT WE "PAINT or COAT" the concrete with a waterproofing SEALER ?? I have used products such as DryLock for VERTICAL, damp walls (such as basement walls) but they do NOT suggest it being used on any horizontal surface. Does anyone know of a product we can brush or roll onto the concrete slab to "seal out" moisture ?? Please help as we really want a "laminate" floor and not the traditional carpet or any more cold, hard, tile in our living room, family room or hallways.

Follow-Up Postings:

RE: Excessive Moisture Concrete Slab Sealing

Hello Florida,
Well, you've got quite a problem. You do NOT need a moisture test. You have done that yourself. If you are getting moisture under plastics, you have moisture. You don't need to pay someone 150.00 to tell you that.
Unfortunately, there are really no sealers that I know of that can handle that amount of moisture. If you paint or coat the concrete with a surface sealer, then you will have peeling and chipping paint or sealer ... probably within a couple of months.
Short of tearing up the concrete and putting a proper moisture barrier down, there are few choices. Try a penetrating sealer that is made to combat moisture. That may help a bit, and for a time, but it will not be permanent (so you will need to recoat frequently). Second, I do not recommend that you cover the floor with anything that can either soak up moisture (like carpet), or stop the movement of moisture (such as laminates.. which will swell and disintegrate). Either of these choices can make conditions perfect for dangerous molds. I suggest you consult a concrete floor specialist, and ask them what they recommend. They may say that your best bet is to stain the floor the way it is, and may be able to help with the hard choice of picking a sealer. Don't go with any acrylic sealers, as they will absolutely peel off.

RE: Excessive Moisture Concrete Slab Sealing

Pull back the carpet, and using duct tape and a 2' x 2' square of clear plastic, tape down the square to clean concrete. Do this in several places. See if condensation builds under the plastic, or the concrete turns darker in color under the plastic.

What you may be seeing is dew point in action, more the vapor emissions.
look at vaporSeal.

RE: Excessive Moisture Concrete Slab Sealing

Thanks to both who responded :-) !! Question for floorguy .... checked out VaporSeal SB and DB, a bit confused as to which is best for me ?? SB has a longer working time but DB is "better adhesion to concrete floor" ?? Am I reading the specs. wrong ??
FWIW- Several other homes on our street (neighbors) with same age, style builder, etc, houses either went with a laminate (put down themselves) or had professional install new carpet. One in particular was "forced" to have new tile and carpet installed as these 20+ year old homes are getting pin-hole leaks in buried (in slab) copper water pipes forcing a CPVC "re-pipe" through attic and down walls.

RE: Excessive Moisture Concrete Slab Sealing

We had a similar situation. Our home is in SW Florida, and is almost 40 years old. It was the house my husband grew up in...we bought from his mother.

In our remodeling of this house, we decided to put HW down in the "rec room" and dining room. The "rec room" is a sunken (5 inches lower) area on the South side of the house. While we've had no problem with the Brazilian Cherry floor in the Dining room, the entire Rec room had to be redone, as we had terrible buckling and warping of that wood.

Our original installer had done NOTHING to the floor before the install. (We had someone else come out and tear that floor out and do the new one.)

We had the same situation you describe with the moist areas underneath anything that sat on the concrete also. When we did a calcium chloride test, there wasn't anything for the lab to test because there was so much moisture!!

Here's what we did, and I know this will be met with some disagreement. Our installer contacted the Bostic company who suggested their MVP product. They said if he covered the entire floor, repeated the Calcium Chloride test and got acceptable (verifiable) results, they would stand behind their product, and the warranty.

He did just that, painted a coating over the whole floor, and retested. AMAZINGLY enough, it did block the moisture and he went ahead and reinstalled a beautiful BR-111 Brazilian Cherry floor. It's now been down 4 months and we haven't had any problems. (THe other floor warped within weeks of installation.)

I KNOW THIS ISN"T THE SOLUTION FOR EVERYONE, AND I KNOW MANY SUGGEST "NO HARDWOOD OVER CONCRETE"!! But if you're like me, you live in Florida, you know there are plenty of Florida Homes with HWFloors...there must be a way!!!!

This is a GREAT forum...with many knowledgable folks. I just wanted to post my experience. Not saying it's the right way to go, just what we did in a similar situation.

Good Luck!

RE: Excessive Moisture Concrete Slab Sealing

graffster, THANKS ever so much for your very helpful information and sharing your experiences. Not to go "off topic" but we have moved to Florida 7 years ago after 48 years of living in Connecticut, slipping, sliding, and freezing during the long winters (not that we don't "fear" Hurricanes here down South). Construction down "here" (South) is entirely different than almost anything up North. I grew up with large attics, basements (dry), large yards and neighbors being HUNDREDS of feet (not 10 feet like here) away from the perimeter of our house.

I am just glad we have no "cracks" in our Florida slab. I have walked many newly (2004-2006) constructed homes only to see multiple floor cracks before the walls were even sheetrocked. Our present "mid-priced" house was built in 1987 and although it may not be up to the current "Florida Hurricane Codes" the exterior, framing, brickwork, trimwork, and overall finish construction (in MY opinion)is far, far superior in MANY ways to any of today's "quickly/cheaply built" homes (except multi-million dollar ones).

Our last Florida home had a pool and the Lanai in the rear and was 15 feet from a large Lake, which means the house was about 40 feet from this huge body of water, The house was a lot "cheaper" in build quality and somewahat smaller than this one, but still built on "wetlands" (actually an old forest of Water Oaks) and did THAT house have any "wet concrete"............ NO !! Figure that out ?????????

RE: Excessive Moisture Concrete Slab Sealing

most of the sealers out there require that the floor be shot blasted or ground before you put the sealer on. and with bostiks mvp it is a great product but it needs to be used with a wood flooring glue down installation and laminate is a floating installation. but you should still have someone come out and do a calcium chloride test or an rh test just to see how much moisture you are dealing with

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