I just completed a shop building with a slab floor. The floor has a vapor barrier under the slab, but not the footings. We have been having a lot of rain, and the slab floor is damp along the walls, extending 2″ to 3″ beyond the sheet rock. The windows are well flashed, and the fiber cement siding is well caulked, so I’m almost positive the water is not in the walls.
The outside of the slab is wet, but would that cause the edge of the slab to be wet 6″ in from the edge? Anyone have any ideas or solutions?
Replies
It could very easily be the water wicking thriugh the concrete.
Who ever invented work didn't know how to fish....
Do you have gutters and downspouts with extensions to get rainwater away from your footings?
Al Mollitor, Sharon MA
No gutters, but there is a 24" overhang of the roof beyond the walls.
The floor has a vapor barrier under the slab, but not the footing.
Are you saying this was a monolithic pour? If so , follow the advice about getting the ground water away from the slab edge. The next question is how close to the top of the slab is the exterior finish grade? I have poured a lot of monolithic slabs and footing and always try to get them at least 8 inches above finish grade. I also seal and/or paint the slab edge if I think there will be water laying agianst it. In one case I had to install a drain tile around a slab to move the ground water way. I dug the tile trench directly beneath the drip line of the roof, and also installed gutters. The problem went away.
BTW when I get jobs like these now, I reccomend insulating the exterior edge and at least two feet inside beneath the slab. Makes for a little more comfortable winter floor temperature.
Dave
Yes, it was a monolithic pour. There is 6" between the finished floor and the ground on the uphill side and 10" on the downhill side and adequate slope away from the building on both sides. No water is standing near the foundation.
Could you give me a recommendation for a sealer I could paint on the side of the slab?
I have used a product called Dry-Lok and another from Sears supplied by a customer. I think any good exterior masonary paint works. You just need something to form a barrier between the concrete and the ground water to break the capilary action that is sucking the water into the edge of the slab.
You mentioned that this is an unconditioned space. Does the dampness show up after you run some type of temporary heat? It could be condensation forming at the cold edge of the slab. This can occur as late as 24 hours after the heat is turned off.
If your fall/winter has been as wet as ours, you may have to wait untillspring/summer to get it dry enough to seal. I have got dead trees falling al over my lot, because the ground is so saturated.
Dave
slab should be at least 6" above adjacent grades (somebody else suggested 8 which is even better) and the ground within the first 10 feet should slope away at least 10% (1 foot fall per 10' horizontally) if you can't meet these conditons describe what you got and I might be able to make recommendations on a band-aid fix
how far beyond the walls does the slab extend on the outside of the building? do the roof overhangs cover this by ???how much?
The slab does not extend beyond the walls. I have good clearance above grade and adequate slope away from the building. The ground is saturated ( clay soil) but no water is next to the slab.
Since this is an unconditioned space, I did not put any caulk between the slab and the PT bottom plate. I did caulk the inside of the plate at the floor to try to keep critters from crawling in. Could this be the cause?
No drainage.Mr T
Do not try this at home!
I am an Experienced Professional!