I almost did a bad thing...

  • Fri 09 February 2018
  • misc

Mrs. RS and I have long wanted to get rid of the ugly beige wall to wall carpet in our house, and we finally got material selected, a contractor lined up, and a plan to tile the entire house except the kitchen (which hasn't been remodeled yet, no need to do it twice.

We are planning on building an extension on the house with a master suite upstairs and a garage downstairs, so we bought plenty of extra tile. About 2000-2100 square feet of it to be exact.

I didn't know how heavy porcelain tile is. I mean, a dinner plate is made of porcelain and it's 2/3 of a square foot and not heavy at all, right? I asked but didn't get a perfect number from our floor guys, so I figured on the heavy side we might have a couple of tons.

I was sure wrong. The tiles are pretty thick, approaching a centimeter, 1' x 2' and come two in a box... which weighs about 46 pounds. So somewhere in the neighborhood of 24000 pounds, give or take.

Once I realized this, it was pretty clear that my clever plan of putting most of it on pallet racking in the basement (with the balance sitting directly on the floor) was going to be a non-starter. That's four 5000 pound concentrated loads on the basement concrete slab, which are spread out to a little less than a square foot each with the scrap aluminum plate I got from a friend underneath the rack feet.

Did you know that most residential basement slabs don't have rebar in them? They're supposed to have some kind of reinforcement but it is usually the stuff that looks like hog panels - welded mesh with wires on a grid layout. It's called "welded wire reinforcement".

International Building Code has fairly lightweight specifications for live loads in residential structures, 40-100 pounds per square foot uniformly distributed and no concentrated load specification. Compare that with office buildings which share 50-100 pounds per square foot and 2000 pound concentrated loads, and manufacturing which is 125-250 psf uniform and 2000-3000 psf concentrated.

Even though the concrete is typically 3000-4000 psi strength, that's in compression. If the slab flexes at all (and it will), there's a tension load. That's what the rebar helps with.

With an appropriate load spreader under each foot, on a ground floor in a building designed for manufacturing, I'd have no trouble with putting 12 tons worth of tile in shelving. But my basement slab is only a fraction of the thickness of such a slab, only a fraction of the strength, and doing this was likely to crack the slab, or worse.

Solution: We're going to get a shipping container to put in the yard near the barn for the tile (and other stuff that I might wish to store in it) to live in.

When we have the garage built under the master suite extension as well as the shop, how will I get a stronger slab without going broke on labor having people hand tie rebar?

I think the solution is going to be a thicker slab, plus welded bar mats and a consult with a structural engineer about what I'm trying to do. Seems you can get a welded mat of rebar which looks from a distance like the aforementioned hog panels but is made out of rebar instead of wire. Might need a double layer, might not, but regardless we should put a layer of foam on the bottom and some PEX in the middle for radiant floor heat... just in case. :)