Advice on plans for shop floor

[Chuck Dvorak]

Hi, all.

I'm planning on laying a plywood floor over the concrete slab of my workshop, which is a converted detached garage. After a lot of reading (and several different directions of advice) I am planning on the following:

1) Putting down a layer of Platon over the concrete slab, then caulking/taping to seal all seams and the perimeter.

2) Over the Platon, a layer of 3/4" Foamular 250, a high-density extruded polystyrene product which has a compressive strength of 25psi. It is tongue and groove and would be run wall-to-wall.

3) Then the top layer--3/4" tongue and groove plywood with 1/4" gap on the perimeter to allow for expansion.

Note: The Platon would be caulked, as mentioned above, but I would not fasten down the polystyrene or plywood. This is both because I don't wish to puncture the Platon, and also because it doesn't seem necessary.

Does this seem like an adequate design? I thought it might be helpful to glue the T&G connections of the plywood and possibly seams that are not t&g (with glue or biscuits/glue).

Any advice is very much appreciated. Thanks!

Chuck

[lawrence dosson]

chuck
I have been thinking of doing this exact same thing I belive most every one uses sleepers under the plywood but i would like to just do what your thinking T#G plywood over the foam board glue the edges and forget the sleepers ..
BUT and thats a big one i lurk here to learn and i hope someone has done just this very thing and can give a yes or no from experience lawrence

[Joe A Faulkner]

Hi Chuck, welcome to Sawmill Creek. I've not been been a contributer that long, but I find this forum extremely helpful. I am in the process of a total shop remodel myself, and am looking at various options for putting down a raised floor in a situation similar to yours. You might find the following threads interesting reading. The are folks who have used sleepers, and fastened them to the concrete, folks who have used sleepers and let them float. I've seen somewhere atleast one suggestion to do something similar to what you are suggesting, but using tapcons to secure the decking to the concrete floor. My main objective in putting in the floor is comfort on my knees, back and legs and temperature control. I'm not yet to the place in my remodel where I am ready for the floor system, so I still have a chance to change my mind, but I think I'm going to go with 2x4 PT sleepers, 16" OC, over visqueen, layed flat, with 1.5" rigid foam. I'm not comfortable having rigid foam bear the load of machinery, traffix, lumber etc which is why I'm going with the sleepers. I am in a situation where I have about 3 1/4" clearance on my service door, so someday I may put down utility grade hickory over the plywood decking. Are you trying to keep the profile of your "raised" floor as short as possible? I recall one creeker ripped 3/4" PT plywood for his sleepers.

Here are the links to some of the other threads:
This one is to my shop remodel question similar to your post:
http://www.sawmillcreek.org/showthread.php?t=135593
Check out Michael Heffernan's replies.

This one is to a post for a floor in a basement. Tom Hamilton describes the "floating" sleeper method". He sent me a pdf which I can send to you if you want to give me your e-mail.

http://www.sawmillcreek.org/showthread.php?t=137170

And then this thread started by George Bregar who used a product similar to what you are considering - delta-fl. I don't know if all of these options help. I'm not sure there is a right answer here. I'd be somewhat uneasy about having 3/4" sheets of decking just floating. I'd be concerned that they would move or warp. If anyone out there has done this, I hope they chime in.

http://www.sawmillcreek.org/showthread.php?t=128924

[Dwight D Baker]

Hello Chuck,

If your plan ultimately turns out to be a good method I think the only thing I would add to it might be tempered 1/4" hardboard on top of the plywood using 1" bugle head screws to fasten it. Obviously you would need to countersink the heads flush with the top of the hardboard, just be sure it truly is tempered hardboad. One other thing worth mentioning is have you checked to see if there are insulation boards able to withstand greater PSI than 25?
The advantage to the hardboard would be when it gets messed up you can replace sheets as needed.
Another alternative to the 3/4" plywood would be the 50 year warranty AdvanTech OSB. It is very hard and as well it is also T&G. I used it in a bathroom remodel for the subfloor and am very impressed with it.

[Joe Cowan]

I am finishing mine this coming weekend by putting the finish floor down (3/4" red oak T&G). I put down plastic and then dry PT 2'X4's no longer that 3' in length. I did not tapcon them down. I then cut the rigid foam insulation on the table saw and placed next to the row of 2X4's and continued on until I had covered enough to start putting down the 3/4" Advantec from Home Depot. I screwed the subfloor to the sleepers with decking screws on approx 12" centers. This floor "floats" on the concrete and has been down about 3 weeks so far.

[Joe A Faulkner]

Joe C, I was looking forward to hearing your experience with the hickory? What changed your mind? Are you going with a utility grade red oak or something a step up from that? Are you planning a finish?

[Joe Cowan]

I bought the $1.59/sq ft red oak from LL. I got fearful of the utility grade hickory as the waste should eat some of the sq footage savings against a higher quality wood. The red oak is perfect for my shop, some insect holes and various small defects. I am the landlord for the local LL and they gave me a small break in price, so the difference was not worth it compared to the hickory.

[Joe A Faulkner]

Is this a prefinished or unfinished product? If the later, what are you plans for finish?

[Jeff Mackay]

I'm doing something similar. I'm planning to put tacton on the floor, with seams taped, and plywood directly covering the tacton, screwed on 24" centers to the concrete, no sleepers.

I've already got 1" foam applied (Foamular 150 outside the poured basement walls, and Foamular 250 under the slab). I also installed R13 fiberglass in the stud walls. Tacton was applied to the exterior walls right after they were poured and before backfill.

Hopefully, I'll be done mudding drywall this weekend and be able to install the tacton and plywood next weekend.

If you're worried about the Foamular carrying the weight of your equipment without sleepers, test it out first. Get a sheet of foam, cover it with a sheet of plywood, and put your heaviest machines on it. I've got 2" Foamular between pre-stressed concrete panels and a 4" concrete slab, and park 3 cars on it every day. But a car tire, combined with the 4" slab depth spread the weight of the car to a pretty wide area.

I looked at Lumber Liquidators for utility grade white oak flooring. They didn't have any in stock, so the cheapest I could get was $2.09 a square foot. I passed. Plywood will do just fine. I'll probably paint the plywood with an epoxy paint.

Jeff

[Lee Koepke]

The only comment I would have is putting a vapor barrier (visqueen) on TOP of the concrete slab. The problem there is, you most likely have a vapor barrier under the slab already, and because of the thermal mass properties and pourous qualities of the concrete, you run the risk of trapping moisture between the barriers and creating condensation / moisture problems down the road.

Sleepers, insulation, and a floating floor should provide enough ventilation to keep moisture from condensing under the plywood floor.

[Joe Cowan]

Is this a prefinished or unfinished product? If the later, what are you plans for finish?

Unfinished. I am planning on sanding to 80 grit and putting a water based clear finish (for now) on this floor. I do not want it real slick, so thinking to 80 grit may be rough enough. What do you think? I am going to investigate this soon, as the floor will be nailed down this weekend.

[Joe A Faulkner]

It Depends. I know some have expressed concern over a poly finish being too slick, especially when fine dust settles on it. All I have ever had is concrete in the shop. I know several folks put epoxy paint on concrete and some have commented about adding sand to make the floor skid resistent. My property is on the older/rustic side. I might be tempted to go with BLO or Tung Oil knowing that the floor will get dinged up. Hopefully some folks with finished hardwood shop floors will chime in.

[Chuck Dvorak]

Thanks to everyone for the comments. It's a good idea to test the Foamular's compressibility. If it can handle 25 psi, I believe that would mean a 8' x 4' sheet with 8' x 4' plywood over it spreading the weight could in theory handle approximately 4600 lbs. On a single 4' x 8' section I should be able to fit my several heavy shop machines, myself, and a large sandwich no problem. And of course the machines will be spread around the shop.

I'm thinking of laying everything down, no sleepers, unfastened to the floor, and see how it works. If I find the floor to be unstable I could always follow up with tapcons. I'd prefer not to puncture the Platon subfloor if not necessary.

Chuck