Concrete Free Slab Infill
Hello,
Maine zone 6. I am doing a concrete free slab within a fpsf style bathtub curb. Standard wing insulation, 4 inches of rigid below floor. 2×4 sleepers will rest on my EPS foam, which will be capped by a vapor barrier.
As a cost saving measure, I am hoping to use either of these for infill, in 6 inch lifts, compacted with a plate compactor:
1. Crushed dust (Ledge): 6$ a cubic yard
2. Sand Fill : (5$ a cubic yard)
I will have a combined radon/water 4″ drain to daylight on each side of the bathtub curb, all the way around. The gravel options are much more expensive, and I figure I can forgo the standard 2 inches of fines on top of gravel if I use either of the two above.
All of it will sit on a very solid 6 inch compacted gravel base that we did this fall. The top soil was scraped away and we laid down geotextile fabric before we laid the gravel. The gravel will freeze and thaw all winter and be very solid.
Comments appreciated.
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Replies
Stephen, the "bathtub curb" term confused me at first but it sounds like you're doing a frost-protected perimeter grade beam? In any case, sand is a pretty common material for fill where it's readily available. According to the IRC, compacted sand can support 2,000 psf whereas sandy gravel (how I would categorize stone dust) can support 3,000 psf. (https://codes.iccsafe.org/content/IRC2015/chapter-4-foundations#IRC2015_Pt03_Ch04_SecR401.4.1) Either one should be enough for most purposes; I would only be concerned if you had large point loads, but even then, I and most engineers I know use 1,500 or 2,000 psf for assumed soil bearing capacity.
Thanks Michael. That's right, its a grade beam. My engineer calls it a curb.