Installing post footing in basement floor

Mark · 2006-11-02T15:11:13+00:00

Good morning.I am nearly ready to replace my 4x4 basement support post.As part of this project, I plan to cut a hole in the slab andpour a proper post footing using an 8" sonotube, A SimpsonCB64 bracket, and a bag of 5000psi Sakrete.I will try to keep the hole small so that the sonotube is afairly snug fit. . .may an inch or even less clearance all around.My question is, how would I properly fill the gap between theconcrete pour and the side of the hole? I have a couple of ideas:- Pour concrete around the outside of the sonotube during theinitial pour. The paper would be left in place in the "underground"portion, and removed where the footing projects through the slab.- Remove all of the sonotube after the concrete sets up. Backfillaround the footing using (what?)Other suggestions?Thanks-Mark

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Mark 19 years ago

So is there a consensus here that my proposed new footing is going to settle? And is settling to be expected even if I make it 2' by 2' as Bob has proposed?

If I jack up the beam 1/4" in anticipation of settling, the result will be damage to the structure above the beam.

If I load the new post with the beam at its current level and it settles 1/4", the result will be damage to the structure above the beam.

The existing post has rested on the slab for 75 years, and I have no particular reason to expect the slab to fail (or to settle) if I put the _new_ post on the slab. Barring a slab failure, this approach produces no damage.

So this brings me full-circle back to the issue that we were discussing last week Except now it appears that I _can_ expect damage if I pour a new post footing instead of resting the new post on the slab where the old post rested.

-Mark

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RicodJour 19 years ago

If the footing is placed on undisturbed soil there is no reason that it would settle unless it was an insufficient, small footing.

You mentioned that the bottom of the beam had crushed fibers at the post. You should take a laser level to the floor above and see if the floor dips at the beam. If so, jack it up slowly to prevent cracking. About 1/16" per day should minimize cracking. If it hasn't settled and you don't need to straighten out the floor, then just jack up the beam enough to take the load off of the post and maybe a bit more. 1/8" is all you need. Again, this should be done slowly to minimize cracking - particularly if the house has plaster walls and tiled floors above.

It shouldn't settle.

My original advice was to saw cut the slab and place the footing on top of it. The footing would not have to be quite as large nor deep if it were on top of the slab. Build shelves around the post on top of the footing if you'd like.

If you continue back full circle, check out my advice on placing the footing on top of the slab. Thanks.

R

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Bob Morrison 19 years ago

No. As I just said a properly sized footing on undisturbed glacial till will not settle.

Raise the beam to level + a little. 1/16"-1/8" would be plenty. This has nothing to do with settling and everything to do with being able to install the new post cap.

Still doesn't make it the right solution. If you do the work properly and carefully there will be no damage to the existing structure.

No. Wrong answer. If you don't want our advice then don't post questions. I have given you a solution that has worked many times with no damage to the existing structure. If you don't want to take the advice, then don't. Just don't complain when you have problems down the road.

Overall, I think you are obsessing over this too much. If you had shored the beam, cut the hole, and poured the concrete last week, you would now be done with the project.

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Mark 19 years ago

Bob, I am not questioning your advice one bit. I was just following up because someone else on the list chimed in with "It's gonna settle. . . you'd better jack it up 1/4" first." Being prone to paranoia, I thought I should follow up on that.

Oh, no doubt about that. Unless of course the 2' x 2' hole filled up with water courtesy of the current "pineapple express" we are enjoying here in the PNW. =8-o

Hmm. . .maybe I should have you take a look at it. I actually have several basement support issues that need attention. Are you interested in a few hours of on-site consulting in Seattle?

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Bob Morrison 19 years ago

That was bad advice. As both Rico and I have pointed out you want to be just above level. This is usually 1/16"-1/8"

If that hole fills with water you may have some serious drainage problems. BTW, thanks to that "pineapple express", my power has gone out 4 times since last Friday afternoon.

Probably not economically worth it for either of us. However, if you want a structural engineer to look at the situation, here is a reference list in PDF form:

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