That sinking feeling...

[MattL]

Hi All,
I am close to completing my Pompeii NZ build, however when boxing up for a small final concrete pour yesterday I noticed that that the boxing (which was plumb) did not match the line of a previous construction joint (which was once upon a time plumb). Long story short, the oven is slowly rotating, having moved approx. 20mm forward to back and 10mm side to side in differential settlement.
Has anyone had similar issues in the past? I have constructed the oven adjoining the deck so I have begun removing the decking timber with a loose plan of installing some piles in front of the slab and doweling back into the slab to prevent further rotation.
Any ideas gladly received. Cheers!

[azatty]

Re: That sinking feeling...

The surface under your slab obviously isn't stable, and it sounds like you don't have footings to support and hold your slab in place.

I don't think "bracing pilings" will fix the problem. I think you want the pilings and slab connected. The last slab I had engineered for an addition to my house called for attaching new slab to existing slab with 1/2" rebar epoxied 6 inches into the old slab, 12 inches into the new slab, and the rebar "pins" placed 18 inches apart. Follow those specs and I'm fairly confident the slab won't be moving.

So I might cut a 30cm square from each corner, and dig a piling down to bedrock (or to stable soil). Then I'd drill into the slab at least six inches on each side of the notch you cut from the slab, and epoxy in some 60 cm, 1/2" re-bar bent in half at a 90 degree angle. Point the end down into the piling, the pour your piling even with the top of the slab. The epoxy is stronger than the concrete, so your slab shouldn't move (unless your pilings aren't on stable ground).

[Neil2]

Re: That sinking feeling...

You can try the same technique used to stabalize the leaning tower of pizza.

Add weight (lots of weight = 1/2 weight of slab or more) to the "high" side of your slab to force settlement there. This may take time. When oven is nearly back to level, remove this extra weight. Note that some slope, around 1% or so, towards the door is desirable.