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I will be incorporating 250 sq. ft. of attached gararge into my downstairs floorplan and adding radiant floor heat in the process. Currently there is no vapor barrier or insulation under the slab. It is otherwise sound. It lies about 3-1/2″ below the eventual finished height at one end, and about 6″ below on the other. I would like to add a layer of 6 mil poly, 1″ foam, 6X6 wire, the PEX tubing and then place the new slab on top. That would leave only 2-1/2″ at the high end. I assume I would need a small aggregate and a rich mix. Is this a good idea or should I remove the old slab and backfill? Any advice on mix design if I do overpour?
Thanks,
Jerry
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Hi Jerry,
a couple of concerns come to mind.
Pouring any slab over an existing sloping slab would be the first.
Having only 2 1/2 inches of concrete (with mesh and tubing sharing the space) over foam in a garage would be a second.
Location of the project and condition of the existing would be a third.
On the face of it, I would vote to remove the existing, do a proper compaction after leveling with a good granular, install the SM styrofoam, (don't need VB if you use shiplapped SM) plan on using at least 4 inches of concrete. Consider using fiber re-enforced mix for your concrete.
Gabe
*Gabe,Thanks much for your response. I share your concerns exactly and removing 250 sq. ft. of slab is no big deal. I only wonder if I'd being doing extra work with no gain. In fact, I was wondering if the finished slab would be better by leaving the old slab under.Let me clear up a few things: The slope amounts to about 1/8" per foot.The space in question becomes heated living space, never to be used as a gararge again (Long Island, NY).The existing slab is in perfect condition.2-1/2" worries me a little.Wadda ya think?Jerry
*Hi Jerry,the problem with the variations in concrete is both a finishing and a structural problem.With only 2 1/2 inches, your mesh and tubing will not have the space to allow enough concrete cover and will dry out faster during the finishing.Putting in a slab with heating costs a fair amount of money and taking out the old slab and doing it right will ensure the investments lasts as long as the payments.Good luckGabe
*Gabe,Well said!Thanks Again,Jerry