Leveling Existing Slab with Builders Sand?
Hi All,
Location: Seattle
Climate Zone: 4C
I will soon be ready to install the flooring in a detached garage (10’x20′) that I am converting into a conditioned workshop. The existing floor is a concrete slab with a professionally installed epoxy coating, over which I plan to install a 15mil vapor barrier, 2″ of high density EPS foam followed by two layers of 3/4″ AdvanTech. The existing floor is out of level across its width and is not flat along its length. The variation is anywhere from 1/4″ to 1 1/2″.
My original plan was to set up screed rails along the length of the garage and use them to apply a thin layer of high-strength ramping mortar across the entire existing slab. However, this option would require complete removal of the existing epoxy coating for bonding, which would be incredibly expensive even if I were to do it myself (diamond cutting inserts aren’t cheap!). I should mention that self-leveling compound isn’t an option here either, as the slope of the existing slab would create an unacceptably large lip at the front of the garage.
Given these constraints, my alternate proposal is to install tapered PT leveling skids every 4′ or so across the width of the garage and to infill between them with builders sand (using the skids as a screed). I would then place the vapor barrier on top of the sand and follow with the EPS and Advantech flooring.
I recognize that the PT skids would be on the wet side of the vapor barrier and prone to eventual rot, but I think this is likely OK given the hefty and dense material sandwich sitting above. Any thoughts on the suitability (or lack thereof) of this approach would be greatly appreciated.
Cheers,
-Adam
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Replies
Adam,
Sounds like a good plan. You might consider mixing a few of bags of Portland Cement in with the sand. Not to make concrete, just so the sand stiffens a bit over time.
Thanks for your reply Malcolm. Are you effectively suggesting a dry pack mix (4-1 sand to Portland Cement) but without the water? Thinking that over time any migrating moisture will stiffen the mix beneath the floor?
I ask only because I'm concerned about bonding to the epoxy, which is what led me to sand in the first place. Probably overthinking this, given what's sitting above, but I'd like to avoid any hollow spots or creaking sounds underfoot.
-Adam
Adam,
Thinking about it again, you are right - just sand is a better solution. I don't see any downside to what you are suggesting.
Seems like a lot of time, money and effort for a tiny thermal improvement given your mild climate.
To my ear the proposed floor does not seem to be much softer under foot.
The epoxy over concrete is a fine floor for a shop.
Walta
Sharp sand and portland cement at a 7:1 ratio will make a good base for leveling and dry stiff (mix with enough water for it to darken & clump). If you use tapered screed boards, you can carefully lift them out when the mix is dry and fill the voids they leave with more of the sand/cement mixture, up to the screeded surface and you will have a wood-free, level base to work off of.