Concrete slab

[EddieWalker]

Okay went through this entire thread. I have a two car detached garage cut into a hill in the PNW. Lots of ground water, rain, but soil does drain pretty well. My slab in the winter usually, gets moist to downright wet patches throughout. It is not a leak from above or coming in from the sides! Puddles throughout and isolated. Pad seems to just get saturated in spots. The garage was built on a slab so no footings. Does seem that some 5/8in crushed was put around the perimeter but no drain pipe. I am guessing no vapor barrier.

My Question: Do you think digging a trench around and below the slab level and using perforated pipe and backfill of gravel will help the problem? How much lower do I need to put drainpipe than the slab?

No water is coming up and through your slab to form puddles or wet spots unless the slab is below grade and the moisture is coming in from the sides like in a basement. If your slab is above grade, on top of the soil, then even if it is sitting in standing water, the capillary action of water in concrete is still not enough to get through a slab. Even a cracked slab will remain dry on top when sitting in water.

You have condensation forming on the floor. You either need to increase air flow, insulate the walls and ceiling better or raise the temperature inside the building so the air can absorb more of the moisture.

Eddie

 

[dragoneggs]

No water is coming up and through your slab to form puddles or wet spots unless the slab is below grade and the moisture is coming in from the sides like in a basement. If your slab is above grade, on top of the soil, then even if it is sitting in standing water, the capillary action of water in concrete is still not enough to get through a slab. Even a cracked slab will remain dry on top when sitting in water.

You have condensation forming on the floor. You either need to increase air flow, insulate the walls and ceiling better or raise the temperature inside the building so the air can absorb more of the moisture.

Eddie

Slab is sort of below grade on two sides. Not directly but very close. It is located on a hill and I have read all of your posts and others on the subject but still feel that there is some hydraulic action going on. So... leaving that argument aside, do you think better drainage around the two high sides will help? I will look into better ventilation but when the air is around 90% humidity here in the NW not much I can do to dry it out. That said, I haven't had this problem before and my current neighbors don't have this problem so I am not buying that it is just sweating from above. I agree with your remedies though.

 

[EddieWalker]

Yes, drainage is very important and the faster you can get the water away from the building, the better off you will be. I'm not a fan of using pipes or French drains, but will if that's the only option. If you can't dig a ditch, then go with the biggest pipe you can.

Eddie