# Floating tongue & groove floor over extruded polystyrene without sleepers?



## intelligen (Dec 28, 2009)

I want to add a quick, easy, and cheap temporary floor in my garage. Ideally I don't want to tap into the existing concrete slab because I may not be in this house for more than a couple more years.

I'm planning to put down some 3/4" blue polystyrene foam, then lay 3/4" tongue & groove plywood over that, perhaps using construction adhesive to fasten the T&G to the foam to prevent the floor from moving around or coming apart. For simplicity and ease of removal later I'd prefer not to mess around with sleepers. My heaviest piece of equipment is 650 lbs. Has anyone done a shop floor like this? If so, how well did it hold up?


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## buildingmonkey (Mar 1, 2014)

Careful with construction adhesive, most formulas will dissolve styrofoam. Check before you buy. Maybe you do not want to cut the foam in strips, to fit between the sleepers, at least you could just forget to nail the sleepers down to the slab. With no sleepers, would expect the foam to compress where your machines set.


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## intelligen (Dec 28, 2009)

Thanks for the warning about construction adhesive.

For now, I decided to run an experiment and lay down one sheet of resin-coated T&G ply over a sheet of foam (without any adhesive), then put my table saw and planer on top. Both tools compressed wheel marks into the ply when I moved them around, but after 2-3 weeks the foam seems to be standing up to the weight just fine. I had hoped that the ply would distribute the weight enough that the foam wouldn't compress too much, and so far that seems to be the case. I'll try to remember to post another update when I get around to moving the planer and saw off the test pieces.


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## Anselth (Apr 19, 2012)

I did something like this without the foam. I used PT 1×2s that I screwed to full sized sheets of OSB. I spaced them on 16" centers like studs, and attached the first one so it overhung the edge. I also moved each one up an inch, so there was a gap on one end. I was then able to lay the pieces down as individual interlocking 4×8 sections. You could do it without the extra spacing work, but doing it this way gave me the ability to throw a screw into the OSB where it overlaps the neighboring "stud" and lock the joint. Even without insulating between the OSB and the slab, it's made my shop floor much warmer and more comfortable. You could easily cut 3/4 inch foam and fit it between the studs if you wanted to, though.

Edit: And you said without sleepers. More tired than I thought.


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## bigblockyeti (Sep 9, 2013)

Given the large surface area between the plywood and foam it would be unlikely you'd have compression issues, if you're saw has an 18" square footprint, at 650lbs. (with the plywood distributing the weight onto the foam) you'd only be looking at around 2psi which should be well below the compression threshold for most any foam that would be used in construction.


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## intelligen (Dec 28, 2009)

Adam and bigblockyeti, thanks for the feedback.

Adam, I really like your idea and in hindsight I'm surprised I haven't run across any other discussions where people described using a modular interlocking solution like yours. It seems like the perfect quick & easy flooring solution, and I can see that it would work just as well without T&G. I whipped up a basic Sketchup model with different views: https://3dwarehouse.sketchup.com/model.html?id=u3ee9d524-8447-4e84-858f-cf7cf017e245

biglblockyeti, that's sort of what I was figuring when I decided to run the experiment, though I wasn't sure how evenly the plywood would distribute the weight or how much it would deflect under the weight. I'm guessing it does a decent job, and at worst I would just need to substitute plywood for foam in the area immediately beneath and around the tools, or I would need to use sleepers under the tools.

Running the numbers backwards, with 15 psi foam I only need to distribute the 426 lbs table saw across 28.4 sq. in. The outer perimeter of the base is about 78" so as you suggested the table saw is well within spec no matter how poorly the plywood distributes the weight when the mobile base is raised.

The planer is 650 lbs but I think the back end is always propped up on the integrated rollers and only the front end sits on the base. If I consider the front and back separately, then for each half (front or back) I need to distribute 325 lbs across 21.67 sq. in. The footprint just happens to be 22" wide so the front is at worst just within spec (but probably well within spec thanks to the plywood distributing the weight). The back is questionable since I think it's always resting on the rollers, but the plywood probably does a good job of distributing the weight. Even if it does deflect slightly, it may not compress the foam very much (if at all).

If it's not too cold out I'll try to move the tools this weekend, and I'll report back on whether the foam sustained any damage. If it warms up enough sometime in the next couple weeks I may try to get a friend to help me lay the floor, most likely using Adam's integrated sleeper idea.


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## changeoffocus (Dec 21, 2013)

I suggest put the heavy pieces on plywood double thick or with sleepers then your foam method in walk surfaces. 
I do like Adam's approach as it remains semi portable. 
I've been wrestling with this issue but most probably would leave heavy metal on concrete and work up to machinery bases.


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