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penywho
Sinking Concrete Porch

My front porch (stoop) is a 5'X 4' concrete slab that has starting sinking at the front and pulling away from the house. To make matters worser, there are pillars that hold up an overhang involved. As the slab sinks, they are pulled forward, which pulls the overhang from the front of the house. Can this problem be repaired, or is the only option to demolish the entire mess and start over?

Mastercarpentry
Re: Sinking Concrete Porch

Here's another "It all depends" kind of answer but it's the best I can do. First thing is to support the overhang so the sinking slab doesn't create further damage; temporary posts on thick paver blocks might do the trick is the soil is firm enough. Disconnect the existing posts and raise the roof till it's where it needs to be. Now to the "depends". Firstly a slab isn't supposed to require a footing(though a perimeter turn-down is often a good idea), the slab itself should be self-supporting atop the soil. Knowing this, it seems that either the soil was an inadequate base or it was made that way by improper filling to grade. If the soil there is universally bad I'd go for a new slab with a perimeter turn-down to contain the loose soil underneath(this, of course, after doing the best you can compacting the soil). If the soil is generally good, then you are a victim of improper filling and/or compaction under the slab. "Mudjacking" or the foam injection technoque used be TOH on the Austin house will work but may be less than permanant, according to the soil it bears on underneath which may continue to sink. Because this slab is small and not connected to the house I think the cheapest most permanant cure is demolition and a new porch slab; just be sure to do whatever is necessary to give it a good base this time.

Far too often I have seen builders who think that there is little or no need to compact filled soil on small slabs and driveways. My answer is always that you can't possibly end up with anything good built on anything bad. Costs sre important to a builder(as in any business)but results are more important, and to try to cut costs by saving a half hour of labor where it's needed is just plain bad business. Had they spent another $5-10 on this slab you wouldn't be having a problem with it now!

MC

canuk
Re: Sinking Concrete Porch

One thing that I see is a problem ...... there should be some consideration for footings under the colums (or pillars) holding up the roof overhang and not merely sitting on the concrete slab.

This way the slab on grade can move without affecting the structure of the roof over hang.

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