Water – How to stop concrete slab floor from absorbing water


This weekend my wife decided to clean up my office. When she pulled the old filing cabinet away from the way, she noticed the baseboards and carpet carpet were showing signs of water damage.

It's a problem I have seen on the opposite side of the house, in our master closet, where I installed a wooden glue-down floor. The floor seems to get wet spots in times when we get heavy rain lasting a few days. I was told it was because I used the wrong glue, and that I should have used a glue that was a water barrier, but it's a closet, and I got the flooring really cheap, so it never really bothered me that I had some semi-dark patches.

Well, I had a neighbor come over that had a moisture meter. We did some poking around, and from all of the signs the water is wicking up: No water in the attic (that we can see), slab is darker, especially near the wall, tack strips show signs of being wet, and the drywall shows signs of moister about 2' to 3' up from the floor, but dry above.

So, to the plan: I am thinking of a multi-phase approach here. First phase, dig about a 6" trench against the side of the house, about 6" below the bottom of the slap. Paint the slab itself with some sort of water barrier, like maybe tar or something meant for basements. Install a french drain and tee it off to about 5' or more towards the neighbor's house, covering the drain pipe against the house with white gravel. Optionally, create a drain field buy digging down a large hold and filling it with gravel as well, but I am not sure if this might be overkill. I would do this on both sides of the house. The front and back do not seem to suffer the same problems.

Second phase is to install gutters around the side and back of the house, making sure to direct the runoff at least a few feet from the house.

So, the first barrage of questions: Is phase one gross overkill? If so, should I just put in some gravel, fore go the french drain part? Would the paint/sealant on the slab cause problems in itself? If now, what would be a good, cheap product to buy to paint it with?

If it helps, I live in Central Florida. The house is about 7 yrs old, we are the only owner. The soil around me is mostly sandy, and used to be an orange grove.

Best Answer

If you don't have gutters and the grading around your house isn't sloped away, I'd start there. It's relatively cheap to do and will eliminate most problems. It's also nice, if you have a door at the bottom of a roof edge, to not enter under a waterfall.

Once you've done that (or if it's not possible to fix the grading) and the foundation is still wicking water, then an exterior water proofing system and french drain makes sense. This involves a painted on sealer, a free draining membrane that's attached to the wall (this gives a direct path for any moisture that reaches the wall to run directly down to the drainage pipe), and a perforated drainage pipe running around the perimeter of the foundation that drains well away from the house. If a system like this isn't installed during initial construction, it's often left to a last resort because of the expense and labor of removing any landscaping and soil that is against the foundation.