Concrete slab weeps moisture

dale h · 04-25-2005, 10:00 PM

How should I treat a concrete slab floor in my home,
that has been weeping moisture, moreso after heavy seasonal rains?
Doubtfull it's a plumbing leak under the slab, but it hasn't been ruled
out 100%. I discount this because of no evidence of pooling of
water around the foundation. Plus, as the rain has diminished this season
and the overall soil in the region has started to dry out, the weeping moisture
coming up through the slab has lessened.

This is a master bedroom, groundfloor, concrete slab, San Diego, clay soil,
with sand and cobblestones. Typically San Diego gets little rain so it hasn't
been a major problem, except this year.
We've lived in the house for almost 2 years. House built in 1977.
I've taken steps to better cope with run off through the overall property....new gutters etc.

After noticing dampness, and musty odor in the room, I pulled back the
wall to wall carpet. The slab has evidence of efflorescence (white powdery, salts, mineral crusts) in some areas. Looks like it has been weeping on and off for some years. Overall the efflorescence isn't too heavy. There is one a yard long fissure that has been spalling, the concrete has been slowly
flaking away (about 1/4 inch deep)....there is moisture at this point, soaking into the carpet pad and coming up to the carpet. Right now it is about 2 feet away from the wall. I hope this condition isn't reaching the walls....at the moment doesn't look like it is.

Ruling out any structural problems from a cracked slab (which is another matter) the major problem is this spalling fissure, damp, with efflorescence building up.

I want to seal up this floor with something that will keep moisture out and re carpet. I've been recomended - trying several coats of dry lock concrete paint or DecoRez two part system.

Any ideas about what to use to patch and seal such a condition?
Thanks for your attention.

dale h

housedocs · 04-30-2005, 02:10 AM

Hi Dale and welcome to the forums. Sory it took us so long to reply, busy time of yr.

Now there's a $50 dollar word for your problem, but it's late, I'm tired & I just can't remember it right now. But basically what you've got is the water table coming up during especially in unusually wet times like you folks have been seeing over the recent past and the water become trapped and pooled between the dense clay soil which doesn't drain well and the concrete and hydrostatic pressure is forcing the water up thru the concrete because it's more pourous than the clay soil during this unusually wet season.

The new gutter may very well alleviate the problem in future situations provided they are connected to an adequate drain system to get the water away from the foundation.

As far as the spalling, once it dries out you can tap out all of the bad concrete with a hammer & clean out the area to be patched real well, moisten it & apply a painted on bonding agent. Then patch in the spot with new cement and trowel smooth, self-leveling cement might even be a better way to go. After that a good waterproofing paint or sealant would be in order, like the Dry-Lock, I've used here in the midwest in basements with pretty good results, I think it's a decent product.

HTH a bit, maybe others will have some further comments over the weekend. Good luck.

Teetorbilt · 04-30-2005, 11:29 AM

housedocs has good info.
You may want to contact E-Bond Epoxies in Ft. Laud, FL. They manufacture an epoxy for the State of Virginia DOT that is dedicated to sealing wet concrete, I forget the name of the stuff right now. I have used it a few times in the past. Unfortunately it smells like dead fish until it cures but it cures very quickly (in about 30 min.). If you decide to go this route, contact me and I will explain how to get maximum use out of the product. The first time that I used it, it kicked in the pan, cost me about $25.00. It was about $50.00 a gallon.