dug out footing, rain collapsed side….
I’m building a 9’x14′ kitchen extension on my house. The plans call for a 16″ wide trenched footing with a 4″ slab on grade. I am going to pour this monolithically. I ws digging out the footings the other day (3 feet deep) and it started raining…HARD! I packed up for the day, but to my pleasure one side of my footing caved in. I’m now not sure what to do, the ground is pretty wet but I’ve got to get this done. I was planning on digging it out again and building a 16″ wide form out of 3/4″ plywood with 16″ wide pieces of 2×4 keeping the plywood the proper distance apart. Then I ‘ll set this form in place and backfill (by hand) against the plywood where it caved in. I’ll tamp it down well. Then after its all backfilled, I’ll remove the 2×4 blocks one at a time and replace them with some 16″ pieces of rebar. This would keep it from caving in again. Then I’ll fill the footing hole with the concrete pour, but I’ll have to leave the plywood in the ground, eventually I guess it will rot away, one sheet will be buried under the slab, the other will be on the out side about 8″ from any future framing. What do you guys think?
Replies
One of the first things I was taught framing was don't sweep off the deck into the hole, backfilled or not. I wouldn't introduce a big billboard made of wood around/under the foundation of my house.
"Eat at Joe's"
But maybe you don't have any termites or carpenter ants there.
I'd overdig and rail the sides. What kind of soil?
A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
spray diesel fuel on the plywood pour the sucker strip the form.
Brace it from the outside
i have had a similar problem,handled it basicly the same way except i filled the forms almost full all around the building then stop pouring ,by then the first area has set 15 mins.then pull all the wood on the inside and continue pouring the floor. i wouldn't want to leave the wood there.if you have to leave the inside form you might look at using 2"m stryfoam for your form board. also around here when this happens you have to go in and dig the bottom out to dry vigin soil again,pure pain in the a. larry
hand me the chainsaw, i need to trim the casing just a hair.
Pouring concrete on mud is bad news. As is leaving any wood under the slab. As the water leaves the mud you'll get a gap--bad. As the wood rots away, or is eaten, it will leave a gap--also bad.
We solve the problem by not pouring monolithic walls/slab that are difficult to brace properly. Others with more demand for such things support the exterior forms from the outside and slope the slab down to the footer so no interior wall or footer form is needed.
Hopefully you'll have time to fix these things before putting mud in the hole.
Good luck,
Someone mentioned over digging.
Just over dig the outside of the trench and put your form there. Clean the inside of the trench of any loose soil and pour the whole thing as you planned.
An extra yard or two of concrete shouldn't break the bank at this point.
Do not put any form on the inside of a monolithic pour or anywhere you can't get it out! The void it creates when it it rots or is eaten by your local variety of pest will be the point on a failure later on.
Dave
I could probably use 2" foam board for the inside form and plywood for the out side. I could get the plywood off the out side if I had to. How would a 3/4" gap if the plywood rots away cause a problem? In my opinion any wood that rots away would be filled in by the grade as it rains, etc. If I backfiiled against the plwood and tamped it down really well wiyth a machine (plate compactor) could I then take the plywood off after a few days and hope the ground will stay?
with all the labor and material to form the hole, sometimes its cheaper just to order couple extra yards of concrete.
I had the same problem with trench walls collapsing because of so much erosion at the base during several rain events! Because I’m doing this work on my own, I decided to use 1/2” thick 3x5 cement board to line my “below the ground” foundation trenches, and used lumber for above ground forms. Considering the cost of cement board versus back breaking labor, it has been a much better solution. Since the cement board will never rot, I can leave in the ground ?
You could build the form to allow rigid foam inside it, against the exterior plywood. That will at least give you a surface on that side that the plywood isn't stuck to if you want to remove it. If you brace the ply from the outside rather than backfilling it shouldn't be a problem. I'm guessing that if your footing is 3 feet deep you're in a climate zone where a couple inches of foam should be part of your plan for the slab anyway.