How should I prepare a wet pier hole for concrete pour?
Question:30" deep pier hole, dug into clay, will be filled with concrete and serve as one of 9 footings for a 10'x12' shed. The hole partially filled with water and I believe it must be dry to pour the concrete. How should I dry it and how dry does it need to be? Should I line the bottom of the hole with gravel?
Answers:
You must live in snow country for a 30" pier for a 10x12 shed. The water won't really affect the concrete at all. Concrete is heavier than water, so the water will come out of the hole as the concrete goes in. Water has to be thouroughly mixed with the concrete to become part of the mix.
While piers are usually pumped out before pouring because the concrete doesn't come up to the top, pouring into a water-filled hole is standard practice on bridges. They usually have such a large volume of water that they pump and pour at the same time. If you can pump it, cool. If not, don't worry about it, it won't affect the strength of the concrete.
rent a small electric submersible pump.
pump out as much as you can.
place 2 or 3 shovelfuls of 3/8" or 1/2" crushed stone in the bottom of hole.
Just before you pour, place the bottom of the pump a few inches down in the stone, and pump it out again. A little water won't effect the concrete much.
Yep. The cement will displace the water. Pour away...
If you feel uneasy about pouring in a wet hole, and you don't want to rent a pump, an alternative method is to pour the concrete into a large plastic leaf bag. If need be, triple the bags. Pour the concrete slowly and hold up the sides of the bags so the water doesn't flow inside them. Works very well with two people doing it.
Good Luck.
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