Was it a Bad Idea? Concrete Stability
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I have a 22′ wide x 20′ deep detached garage. I will assume that it has a thickened edge.
This garage has an 8′ wide x 20′ deep concrete patio that was built at the same time and under a roof that covered both spaces.
I do not know anything about the specifics of the patio slab construction. It is at least 4″ thick, although it could be thinner in the middle. Wire mesh is an assumption, but I suppose it is there. Rebar between the two slabs is doubtful.
I have lived here for 10 years, and have not noticed any additional movement between the two slabs, horizontally or vertically. I had about 1200# of scrap steel piled there on the patio for a few years. The lot where the garage is built is sloped, and there is plenty of drainage.
So, I needs some space. With some help, 3 new walls are erected on the existing slab. Probably done lots of times elsewhere.
There is a 24″ chunk of 14 ga angle that is anchored to each slab with 3/8 wedge anchors where the garage portion is higher due to required floor pitch. Don’t know if it will do any good, but it’s there now. I have leveled off the floor in that location.
I suppose that there are many structures built on slabs just like the one I have.
Now I have a few nagging thoughts that due to the weight of the walls and the stuff inside, things could start moving.
I have a heavy 56″ toolbox (~1700# as it sits now) and a heavier 48″ sheet metal brake (~1900#) that I want to put along the new outside wall. The brake will be in the middle and the toolbox is off to the left. I also have a large workbench that will straddle the garage slab and the old patio slab.
I am hoping that “heavy” to me is not so to this concrete slab.
Any thoughts?
Supposing something starts moving, would mudjacking stabilize things, or does it become a bigger problem involving steel beams, cribbing and excavation?
Replies
I suspect you could park a car on the slab with no problem. The stuff you're talking about is no worse than a car.
With every single you
With every single thing you mentioned that you didn't know........why did you do this work first and now are worrying about it? Why didn't you find out what was right first and ask questions BEFORE you did any work?
Sometimes Stuff Happens
That concrete has been calling my name for a long time, and the opportunity arose to close it in.
I knew about the stuff, just did not allow myself to think about it or process it fully.
Hopefully, it wasn't a stupid move. Guess I'll know soon enough.
What's the worst that can happen? The slab cracks. Not like it's gonna crack your imported Italian tile floor in there.
Tile
Well, I have been eyeng some 18" closeout tile at HOBO...
Just Kidding.
I would be more concerned about major continuing shifting than a crack that stabilizes.
My advice: Don't assume anything.
One of the 'unforseen effects' of having codes is that the 'minimum' standards are instead treated as maximums. Sort of like the same quirk that leads to our treating the 'speed limit' as though it were a minimum spped, rather than a max. That is, you can only assume that the minimum was done - even a few corners cut but not caught - and be sure that not one extra bit of performance was delivered.
For example, you have no reason to 'suppose' there's rebar or mesh in that slab, and you can be certain that it's NOT tied into the other foundation. After all, it's "just a patio," right? Likewise, you have no idea what the composition of that concrete is.
Only if you rip out the old and make sure to 'do it right' can you know if the foundations are appropriate. Forget the slab- what matters most are the footings, the drainage, and the compaction.
Yeah
I know you are right.
At this point, if it goes horribly wrong, I am looking at the same solution to the problem: temporarily supporting the added structure while excavating the old... or, starting over.
Crossing fingers.
I did put a reference mark between the two slabs, so it will show up if it moves.
Next time I have the grinder out, the mark will get more permanent.