Tacking OSB flooring to concrete slab

[Christopher Charles]

Hello all,

I have acquired some T&G OSB at a very attractive price ($0) and am planning to lay it down as a shop floor.

The plan is concrete slab with a layer of plastic vapor barrier and then OSB on top. My question is how to attach the OSB to the slab to prevent wandering. The OSB was free because it's not full sized sheets and I'll also not be going wall-to-wall, but covering the area with my workbench (~12'x16'). I'm imagining some sort of self-tapping concrete anchor, ideally some that are flush when driven.

Thanks in advance,
C

[Jeff Duncan]

Easiest way would be a Hilti gun…..shoot em' quick and easy

good luck,
JeffD

[Don Jarvie]

Put PT 2x4s down flat and then screw the OSB to it. Drilling into the concrete could cause water seeping in and your floor is probably not level so you can shim the sleepers. Also put some hard foam insulation between them. It will help keep the shop warm.

By the way do the whole shop.

[Peter Kelly]

Delta-Fl, not poly sheet, screw down the OSB using Tapcons or similar. As above, do the whole shop space.

[Jim Andrew]

I would consider resale. Shooting nails into concrete makes it very hard to remove nails without damaging the concrete. I'd rather unscrew tapcons if you want to remove the flooring. They won't come out with a hunk of concrete.

[John Lifer]

I'd not nail to the floor either ruin your concrete.

[Andrew Fleck]

I wouldn't tack it down at all. I would just lay it down on top of the moisture barrier and call it a day. 12' x 16' shouldn't move around on you.

[johnny means]

Nailing to concrete does not ruin it. It's pretty much a standard construction technique. Your nails should be one inch longer than the material being nailed. I myself prefer Tapcons. Though they are more work and require a proper rotary hammer for doing anything more than a handful.l

[Greg Peterson]

I vote for PT 2x4 and foam insulation. Wall to wall, no need to tack it down. Added advantage is with that configuration, you can run conduit underneath.

[Don McManus]

My health situation makes concrete slab floors miserable on my joints, so I've done three different floors of 3/4" T+G plywood over sleepers in 3 shops. My "short answer" is the last bullet.
I apologize if this comes off as long and pedantic, but unfortunately, I made a lot of mistakes due to lack of any construction experience. This may be more of a list of what not to do , but here goes:

Floor#1
1) --Glued landscape timbers down on 16" centers with PL construction adhesive. I lost a lot of ceiling height (3.5" +3/4")
--some were on 12" centers under one bay to pull a vehicle into, but the 4.25"combined height was awkward on cars, and miserable for getting mobile bases in and out of the garage.
--6mil Poly between sleepers and plywood. My theory was that the concrete could breathe if moisture came thru slab, so i left the space between "joists" open to the garage door side.
--Deck screws thru ply to sleepers.
--I hoped to run DC pipes in the 3.5" space under plywood...but after reading up on static pressure losses, and pricing duct work, I only ever ran power cords under the floor
--Glidden porch and floor paint....very slippery with by it self, and slick as ice with fine sawdust on top of it.
--The pedestrian door swung in, so I had to leave a square of of concrete 4.25" below the rest of the floor. Many people tripped on the step up when entering. I often forgot to step down while exiting.

Floor#2
2) after miserable resale experience with the adhesive in #1, and a career change. I needed to save money on the next shop. :
--untreated 2x4 sleepers, laid loose on their faces(i hated the lost ceiling height in the first shop.)
--24" centers vs 16" on previous build which was too stiff for my liking. Since 2x4s on faces, technically the plywood was supported a little better.
--6mil poly underneath the bare 2x4's, since they were untreated. This was a gamble in our humidity/climate, but the floor showed zero signs of moisture or rot, when we moved it 3 years later.
-- epoxy floor paint over plywood( Applied in south texas afternoon heat( in July)). Epoxy tacked up in 30 minutes in high temps. Should've stored in cold place before mixing.
-- hoped extra flakes would improve traction over #1, but last half of them didn't stick well to the hot epoxy. I vacuumed up pounds of flakes after floor cured.
--added too much traction additive to epoxy, which made floor feel like walking on 60 grit sandpaper. Very grabby. Feet wouldn't slide, even you wanted them too.
--We used large deck screws for strength, but the 1/4" diameter heads were countersink(only a 1/8"), but unfortunately tool casters would "sink" into them and get stuck.
--We didn't drive the screws exactly perpendicular to the floor, leaving some screwhead edges angling up, which were catching feet and casters on that side.
--no attachment to the concrete. The T+G was screwed every 12" to all the sleepers, locking the enitire floor together so well that it never moves.

3) Last year, i did my most recent floor, which is the best so far.
--3/4" T+G plywood, over 6mil poly, over 2x4 PT sleepers.
--Trim head #6 spax screws at 24" spacing(to avoid caster traps seen in #2). We were also more careful about driving them straight in.
--Painted floor at right temperature, and most of the flakes stuck.
--used about 2 bags of behr floor traction additive across 3 kits of epoxy. This seems to have adequate traction with out the grabbiness of the previous floor, when we used twice as much additive.
-- we learned to used wedges(door installation shims) to "shift" the plywood away from the side walls, and help keep it square while pounding it in.
--keeping the screw heads smaller and more level allowed the epoxy to fill in the star drive heads, and made a lot of them nearly level/invisible.
--I built a "kerf-curved" ramp to allow tools and cars to migrate the height difference to the driveway more smoothly.
--I've pulled a car in on top of this floors without issue.
-- Next time I'd mix in some larger deck screws around the perimeter, and use the smaller spax screws in the high traffic areas. The sparsely placed spaxes were a little too "bendy" when sledgehammering the T+G sheets together, and sheets two courses back would shift when trying to force a warped T+G together.(see below)

Final thoughts :

• set the first piece really, really square. Square it with the long axis of your shop...the errors amplify the further out , so focus on the longest baseline on the first couple sheets.
• an cordless impact really helps drive all those deck screws. Coated screws, and/or a wax stick on the threads helps too.
• We used a sledgehammer and a 4'+ long 2x4 to set the flooring. Put the 2x4 against the tongue to prevent crushing it with the sledgehammer blows you use to set the opposite grove onto the previous pieces tongue. Only hit the 2x4, never the tongue itself, because the next groove won't fit it its tongue chipped,split, or smushed.
• The T+G can curl at the edges enough that you may need weight on the both tongue corners to keep it flat while you pound the tongue in. My girlfriend would sit on the far corner, while I stood on the near corner, which I was hammering. We also used a 5gallon bucket of paint as a weight, where the two of use were too light to flatten it. While the sledge seems like overkill, you have to get the edges tight or the next piece will not line up and you can get an accumulative error where you can't the tongues properly at the joints. Maybe OSB doesn't have curl issues like plywood.
• I never insulated between sleepers, but its not very cold in Houston. The plywood doesn't suck the heat out of your feet like concrete seems to, but it rarely ever freezes here.
• Letting the floor float sleepers over the concrete has caused me no problems with weight or movement. In fact, after the first few sheets are installed the the whole thing becomes near impossible to shift around, even if you need to adjust for for squareness.

Cheers,
Don

[Ruhi Arslan]

Mine is floating over a 6mil plastic barrier on the basement floor. Just staggered the seams. No complaints.

[Joe Cowan]

I vote for PT 2x4 and foam insulation. Wall to wall, no need to tack it down. Added advantage is with that configuration, you can run conduit underneath.

Another vote for this. Just buy dry PT 2x4's and cut them no longer than 3' each, stagger the joints. I tacked some 1/2 strips to the top of mine to match the 2" rigid insulation and then the t&g ply on top. Great floor.

[Jim Andrew]

I don't really understand the need to cut PT 2x4's into short pieces? If they are covered by sheets, they should be protected from sunlight, which is the main thing that causes them to warp. If they fit the floor flat, they should be ok without cutting down. If you are going to lay plastic sheeting down on the concrete, you could go with plain 2x4's as if they are kept dry they will not deteriorate. I really see no need to nail the 2x4's to the slab. The OP was not going to use 2x4's, he was just going to fasten the sheeting to the floor. The 2x4 system would be a better floor.