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Question DetailsAsked on 7/22/2013

water seeps through concrete garage floor rain or shine

38 yr old house. new symptom, not just condensation

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1 Answer


Assuming you have lived there for a few years so you know what is normal, I would start with a couple of checks before paying for a professional. Some of these possible causes might cause water seepage for a week or more after a rain or similar water source event, as it seeps down to the floor level. Some others would cause continuing seepage - I think it is pretty self-evident which is which. These are ALL causes I have seen cause concrete slab dampness, though usually in basements not on-grade garage floors. If you are pretty sure the source is under the garage floor, I would skip to #15 through #18 first, then try the others after that.

1) if you have kids, or grandkids visiting, check they have not been playing with water near the foundation

2) look for a leak at or near furnace or hot water heater that might be going into a crack in the concrete, then appearing as seepage through the concrete elsewhere

3) check for a hose or hose bib (faucet) leaking or left on outside

4) check your gutters for blockage, broken downspout, or downspout flow no longer directed away from the house

5) check for leakage from nearby pool or pool system

6) look around for a new source of water coming in from neighboring yard, or if they have had any recent modifications in land surface grading or gutters that might have directed water to your yard

7) if you have a yard drainage system, french drain, etc check it is not backed up

8) if you have a sump pump, make sure it is actually pumping the water out, and that there is not a significant flowing back down into the sump because of a stuck backflow valve. Also check its discharge pipe is not leaking, or broken and now discharging right at the foundation

9) check any crawl space and basement ceiling for leaking water pipes or sewer pipe, if at or higher than the garage floor

10) check for leaking sprinkler system, or a broken or mis-aimed or stuck sprayhead that is concentrating water toward or near the house. Ditto for weep watering system.

11) check for any change in drainage near the house that is now causing pooling against the foundation or slab

12) check all your inside pipes, under sinks, etc for any signs of leakage, and walk all around the house for any sign of leakage down the outside or inside of the foundation from under the wall or siding - if a continuing issue will be either visible water or lime staining, or mold if on wood or drywall

13) if you have a septic system, check it is not overfull or plugged, raising the surrounding water table locally

14) check that garage floor drain is not backing up when tub empties or washing machine empties, and is leaking under garage slab

15) if a creek or lake or drainage ditch nearby, make sure nothing has dammed it, raising the water table

16) with all water turned off in the house, and with the hot water heater not heating (or turned down to pilot) use a stethoscope to listen to the water pipes for sounds of leakage. Start at the furnace and water heater so you know what the pilot lights sound like (pretty faint), then listen at intervals along the water pipes until you zero in on the leak, if any. You will be able to hear it through concrete slab too, if of any size. If crawling around on a basement slab is too hard on your body, use a metal pipe or rod held against the concrete at intervals, with the stethoscope against that. If you hear something, turn of your main house water shutoff - if it stops, leak is on the house side of the shutoff. Then, if you have a shutoff at the street or outside water meter, shut it off and listen again - if shutting it off there stops the leak (after draining trapped pressure at a faucet) , then if is between the street or meter and the house.

17) dig a hole next to the foundation as close to the wet zone as you can get, to see if the water level is up to the concrete slab level. If not, then most likely seepage in under the slab from elsewhere, or a broken pipe under the slab. If high, check another place or two around the house to see if general or localized. That should tell you if it is an outside source, or something specific to that immediate area. Also, if you have a basement, crawl space, or other lower spot that is NOT wet, that tells you it is definitely NOT generally high groundwater - it is a localized problem.

18) if you water pipe comes into the hosue underground to the utility area in the garage like mine, check the insulation or wrap where it exits the slab - might be leaking where it penetrates the concrete, especially if it was not wrapped before the concrete was poured around ti

If all that fails, I give up - you need an on-site expert. I honestly don't know if I would try a plumber or a waterproofing contractor first, because if I had not found the source by that time I would probably assume either the house was jinxed, or I would turn in my professional certifications due to incompetence.

Answered 6 years ago by LCD

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