I have just had the excavation done for the foundation of the workshop I plan to build. The building will be sitting completely on ledge, with depth ranging from six inches to three feet below grade. In my part of Vermont, that is well above the frost line. The ledge generally slopes in one direction, but its full of fissures and bath-tub-sized pools which collect and hold water. An effective perimeter drain seems impossible. Would filling the cracks and holes with concrete be an effective way to keep water out from under the foundation walls, or am I crazy to even consider building on this site.
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In broad general terms you are building a dam the width of your workshop on a slope and you want to know if it will leak and if frost will want to lift your slab.
Probably, unless you give water an easier route around your shop and you protect your footings from frost.
Is this shop intended to be heated all winter?
Gabe
Thanks for your reply.
The workshop will be heated, but not neccesarily 24 hours a day.
The excavator who did the job said that once the foundation was loaded, meaning the building was in place, the frost would not be able to lift it. I find that a little hard to believe, but if there was a way to seal the junction of the concrete and the ledge, that might go a long way in preventing moisture infiltration. So my question is: Is such a sealent available, and is it effective? Or does the concrete itself provide a water tight seal?
A perimeter drain would be useless because of the uneven nature of the ledge's fissures and caverns.
Thanks for your interest.
I've seen frost lift the corner of a 4 story so I wouldn't put much stock in your excavator's advise.
Make sure the rock is super clean when you pour your concrete, right down into every nook and cranny. Use a pressure wash or a compressor to make sure you get it clean enough to eat off of. Chip out any loose stones. Fill the inside with gravel or crushed stone without any organic material. Install same on outside for drainage as well.
There's some products on the market that we use in parking garages that is a brush applied water proofing that you can use to seal the lenght perimeter of your shed. You may want to install weep holes at the lowest point of your footings to release any water that may find it's way in.
Gabe