A question for the masses.....

[imahic]

Got some down time today for a bit and was looking at a wood working magazine getting some ideas for if and when I ever get back home to play in my shop again. When I bought my place the shop was already in place. it is 20x40 with approx 20x30 walled in and insulated. The other area is open to the ceiling of the metal shop with a 12x12 roll up door. Whoever poured the slab apparently didn't use much if any steel in the concrete and must have had some heavy machinery in there also. The result is some pretty good cracks in the floor. In some places the crack is 1/2 inch wide. I have been filling them in with stuff for quite a while and nearly have them all filled now.
My question is: has any one ever had any experience putting a wooden floor over something like that? My thought is to put down stringers and then put a plywood subfloor over the stringers. Would shim the stringers so the floor would be reasonably level. Are there any hidden problems with this that I am not seeing? I would love to have the wooden floor to ease the load on these old feets. My guess is this would raise the floor between 1 1/2 or 2 1/4 inches depending on what I use as the stringers.
All this is assuming I will eventually get back home for a while before we get called back out on another storm. We are hoping to get back home before Christmas but no guarantees unfortunately. Dealing with these government flood policies is not exactly a speedy process.

Mike

[TDHofstetter]

That can be done... but take whatever precautions are necessary to deal with the moisture wicking up through that concrete. It WILL, a surprising amount. If ya don't believe me, lay a piece of plastic film (even Saran) down on the floor & put something flat & heavy on top of it, then check it a day later - it'll be wet.

So... maybe lay down plastic film on the 'crete first, use PT stringers, and figure something for ventilation - especially around the rim, where moisture can get out from under the plastic.

Or just put down rubber stall mats where you ordinarily stand. You can get 'em in agricultural supply places, for cheap. Allow spaces between any two mats so moisture can escape.

One of the nice things about a wood-framed, wood-floored shop over a crawlspace: You can leave the crawlspace open to ventilate under the floor & it'll be there forever. Concrete has its shining traits, but doesn't very much like to be floored over.

There are also the 2'x2' platform things HD sells - I dunno how well they work, but they look pretty decent from here.

[imahic]

Great point, Tim. I hadn't even considered the moisture but you are certainly right as usual. Now that I DO think about it that might be the deal breaker right there. I have some of those rubber mat things that do help but I have been trying to make everything mobile in my shop and those rubber mats don't make for easy rolling. Thanks for pointing out what should have been obvious to me. That's why I asked the question in here, I knew someone would think of something I hadn't and you came through like gangbusters.....lol.

Mike

[Beamer]

I have done exactly what you are thinking of ... twice

First shop, I didn't bother putting anything but 2x4's down directly on the concrete. That slab looked like a glacial wasteland - there were chunks sticking up as much as 3" above the rest of the floor. Itw as really bad. So I worked around all those lumps to get a flat floor - semi-level with shims. I only used it for 3 years and then moved - it was a rental so I don't know how long it'd last - at least 3 years

Now in my current shop, I laid down 6mil plastic sheeting first, SUPER well taped at each seam. The idea is that if there's going to be any airflow, it needs to be OUT not up into the sleepers. So overlap a good 6" or a foot and tape both seams. It's a pain in the ass, but it's your best bet for keepin' your sleepers in decent shape. Use good tape, not crap tape that won't stick well. In the building industry they use "Tuck Tape" that's pretty pricy. I went with it because I only wanted to lay one floor this time

Once I put the plastic down, then I laid 2x4 sleepers - i didn't bother with PT but i did use KD lumber. My contractor friend asked "If yer goin through all that trouble to seal out moisture, why would you put anything wet on top of it?" and that's the most instruction I got on that. No nails, don't puncture that plastic membrane - just leave 'em lay there reasonably straight. I went 16" OC but you could do 12". Laid flat, a 16" OC spacing yields very little spans between each one.

I almost went with a grid but decided the payoff wasn't that great. The first shop had one and it really was more trouble than it was worth, I think. All the energy trying to get all sorts of pieces both semi-level AND in the same plane was annoying. My contractor friend said not to bother.

On top of the sleepers, I laid 3/4" T&G OSB subfloor. The T&G was nice - it helped lock everything together. I screwed 'em to the sleepers every foot or so. Then I put down 2 coats of Porch & Floor paint (because grage floor paint was EXPENSIVE). I did that at the old shop and it's held up pretty good.

My only gripes are material choices that I made. I put sand in the paint and kinda wish i hadn't. I was worried about things being slippery with sawdust - they had been at the old shop. So the sand helped there, but it pretty much makes sweeping impossible. It takes 50 passes over one spot where one pass woulda done much better if it were smooth.

The other gripe is with the OSB. It's a minor gripe, though. A handful of spots have peeled up a layer or chip of wood. It's not a huge deal, but it looks glaring against a white painted floor.

In searching for floor covering, I wanted to get some of those super smooth tiles that you see in school classrooms, hospitals, etc. You know, the ones with no grout and little flecks of color spattered through out 'em. I couldn't round any up in a reasonable timeframe so that's why I painted instead. If I do come across a deal, I'll pick 'em up and lay 'em on top of the painted OSB if i ever reach my limit with that sand.

Overall - it works great. I can stand out there for 8-9 hours before I start to feel it. I also laid down some anti-fatigue mats in various workstations which really makes things super comfy out there.

[CajunRider]

I helped a friend do a floor exactly like yours. We first bought a few bag of leveling concretes and poured in on the floor and squeegeed it around to fill all the cracks. Then we laid down the plastic sheet and taped in down really good. Then we laid down 2x4 on 16" center. We used cut off pieces to block them into a grid. Then we ran 3 conduits for ground plugs where his table saw, jointer, and bandsaw were going to be. Then we laid down the 1 1/4" plywood subfloor right on top of the 2x4 after putting a healthy bead of construction glue on the 2x4 and a light bead of glue in the groove. The floor was solid, you can drive cars in and out and do whatever you want. There is no sag, no flex.

BTW we left a 3/8" gap between the floor and the wall to allow for wood expansion and to allow the water vapor to escape. Last time I talked to him every thing was still as solid as the day we built it.

[Leo Voisine]

When I did my cellar floor, I sealed it with drylock.

Then I ripped PT 2x4's in half, for stringers 16 OC.

Then I put styrofoam insulation between the stringers.

Then I put 3/4 plywood. Today - I would use 3/4 Tounge and Groove plywood.

Here we are 15 years later - still no problem with the floor.

If I were puttung machines on the floor - I just might consider a double thickness in an alternating pattern of 3/4 tounge and groove plywood.

[imahic]

Thanks for your replies guys. I may still consider it but Tim brought up a good point and I have noticed the floor being damp at times when we do have a lot of rain or high humidity. It is certainly something to consider for sure. The one thing I wonder about is if the dampness would build up between the plastic and the concrete and causing mold to grow. Since my run in with Legionaire's disease, I am a little gunshy of mold now. I don't ever want to go through that again. The doc said since I had it once I could be susceptible to it again maybe. Having your lung scraped out and laying in the hospital bed from hell for 9 days while gunk drains out of your lung is no picnic I can promise you. LOML told me after I got out and recovered that the doctor told her I was knocking on death's door right before they did the surgery on my lung. I knew I felt like hell but didn't realize it got that close. I didn't see any white lights or have any out of body experiences so maybe I wasn't knocking quite as hard as they thought....lol

Mike

[tw]

Whatever you do....do NEVER try to stop the moisture by putting plastic on top of the concrete. You create a perfect greenhouse for all imaginable sorts of mould. The method was quite common here in Finland in the 80-ies and is now considerad a total disaster.

Now everything depends on the climate where you live and on the soil.

In our climate and on our morraine soil theese precautions are necsessary under a concrete floor if it is goint to stay dry enough for adding a wooden floor on top.
-Proper drain pipes all around the building.
-A layer of coarse gravel minimum 20 cm (8") thick to break the capillary suction. (I personally prefere it thicker)
-A layer of at least 10cm (4") styrofoam immediatelt below the concrete. The styrofoam keeps the concrete warmer than the ground below thereby reversing the direction of the steam seeping through the concrete.
-On clay soil this kind of floor should be avoided if possible.

So now you are back to the beginning......What about breaking up the old concrete floor and casting a new one?

Or leaving a ventilated space under a new (properly insulated? )self bearing wooden floor? Then you must make holes through the exterrior walls for ventilation.

Do the load bearing walls stand on the slab or on a separate foundation?

[imahic]

I have actually thought about tearing out the old floor also. But that would involve tearing out all the interior walls and moving everything out of the shop and storing it somewhere. I've even thought about pouring another slab on top of the existing one. Your point about the soil is a good one as well. Where I live it is HARD red clay. When it is wet, you won't sink very far but it is slippery as snot on glass...lol. I would love to have a wooden floor. I just like the way it sounds and feels. When I was a kid, my mom shopped in a grocery store that had a wooden floor and I always loved the sound of that shopping cart rolling on it. For some reason I can still almost hear it now....lol. Well, thanks for all the replies. It sure gives me something to ponder until I can get back home again. After working around all this flooding I am seriously considering getting flood insurance for my shop. The slab is not that high and one of those once in a lifetime rains would surely get in my shop. For sure I am going to make sure all my tools are kept off the floor or lower shelves....lol.

Mike