I would like to install a wood subfloor over the concrete slab in my new shop. I read the article in FW #160 and it suggests the use of a vapor barrier plus screwing and using liquid nails to secure sleepers to the concrete floor. It seems unecessary to put in a vapor barrier when the concrete was poured over a vapor barrier. Also, I would hate to screw holes in the concrete as that might allow moisture to pass through the floor. What about just using liquid nails to secure pressure treated sleepers and then screwing the subfloor to the sleepers? Would that result in too much vibration? Has anyone tried that? Other ideas? Thanks, Lyptus
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Replies
The vapor barrier under the concrete is not a 100% solution.
The amount of vapor necessary to cause problems with a wood floor (far less so with a subfloor, but the usual application is a wood strip finish floor) is quite small.
I would expect moisture problems in a plywood subfloor to produce squeeks, not real problems.
A properly installed concrete fastener shouldn't penetrate the entire slab.
The longer I stayed in construction, the more I believed that one should do things right or stay home.
Good luck!
wood floor?
Lyptus,
Just curious, why do you want to cover the concrete? For comfort? Are you having moisture problems with the slab now?
Are you planning to use 3/4" OSB or plywood sub floor?
I would definitely use 2 x 4 or 2 x 2 treated sleepers on 16" centers. The fastest and easiest way I've found to attach the sleepers is by using a 1/4" roto-hammer bit and while standing on the sleeper, drill right through the wood and into the concrete about 2 1/2". Then put two 12 d HDG common nails in the hole and drive them in together with a 22 oz. min hammer.
You be the judge on the vapor barrier. Have you had any moisture come out of the slab or does it get condensation on it? If I used a vapor barrier I would place it under the sleepers which would render gluing them to the concrete useless. I would glue the sub floor to the sleepers.
I have a concrete floor in my shop. I have never noticed any advantage in a wood shop floor vs. concrete. I'm sure others would dis-agree.
Bret
I want to cover the concrete floor for comfort, to protect fallen tools, and for better insulation against the cold in winter. I designed my new shop so that the cinder-block foundation is only 1" 5/8" proud of the slab so that overlaying OSB or plywood on 2x4 sleepers will make for a floor flush with the walls.
Are there advantages to OSB vs. Plywood vs. other wood subfloor materials?
Also, I've heard that one must let a new concrete slab cure at least 6 mos. before covering it so that the initial moisture in the concrete can escape. Is that true?
- Lyptus
Why wait?
The six month wait, isn't so that the slab can cure, the concrete would cure just fine if it never dried out.
The wait is so that all of the moisture in the slab, and it can literally be tons of water, can evaporate before the wood floor goes down. The thinking is that you don't want all of that water trying to escape through your floor where it can cause problems with wood movement and mold formation. The six month recommendation is just somebody's guess by the way, not a hard and fast rule, but giving the slab several months to a year to dry out is a good idea.
to wait or not to wait, that is the question
For financial and other reasons, waiting 6-12 months to install a wood floor is not be an option for me. My current plan is to screw and glue 2x4 PT sleepers at 16" OC and then cover them with a 6 mil polyethelene vapor barrier. On top of that, I'll screw on some sort of OSB T&G subflooring. The vapor barrier will prevent moisture and mold affecting the subfloor but it will also trap moisture betwen the may trap moisture around the PT sleepers. I assume that overtime eventually this moisture will dissipate despite the moisture barrier but even if it just stayed trapped, would this present much a problem?
- Lyptus
trapping moisture
I'm certainly not an expert, but I'd think that trapping mosture anywhere would not be a good idea. You might end up with some sort of nasty mold beneath the floor. Putting the moisture barrier beneath the sleepers might be a better idea.
to adhere or not to adhere
I like your suggestion about putting down the vapor barrier directly over the concrete slab and underneath the sleepers. However, this will mean that I will not be able to use a combination of construction adhensive and screws to secure the sleepers. Is that construction adhesive really necessary if you are screwing every 2-ft OC? I don't want the floor to vibrate excessively from the woodworking machines but maybe screws by themselves are adequate?
- Lyptus
Why not rip 1" sleepers
Why not rip 1" sleepers from pressure treated 2 x 4's, lay 1" thick styrofoam between the sleepers and 3/4" plywood nailed to the sleepers, i.e. a floating floor? Put down 6 mil poly first. Could also go 2" if you need a bit more insulation. Easy peasy and no damage to the slab. Just a thought.
Could also screw the plywood to the sleepers. Just make sure the fastners don't penetrate the poly.
Here's a helpful link, http://www.hardwoodinstaller.com/hardwoodinstaller/hardwoodonconcrete.htm
Regards,
hats and talking
First, please note that I'm not a flooring expert. I just think about these things and offer thoughts that may or may not be helpful. In orther words, I may be talking through my hat here.
One concern that I have is that the typical poly sheeting forms a reasonable vapor/mosture barrier, but only if it is not punctured. So, some parts of the barrier are compromised everywhere there is a nail or other fastener that goes through the poly. There may be better barriers - self-healing rubber barriers, for example, that "heal" themselves around the concrete nails or bolts and anchors. Or, there may be other methods of creating a seal. I just don't know.
My thought would be that you want a 20-30 year life to the floor, or longer. To get that sort of floor life (as opposed to shelf life ;-) ), you really need to be talking to flooring experts who will provide guarantees for their products, not general woodworkers (even though we're a stellar crowd).
osb vs plywood
Neither OSB or plywood subfloor are designed as a wear surface and not all of these are created equal. Plywood has voids and delam problems, cheap OSB has swelling issues. My vote would be for a "premium" brand of OSB UDL T & G such as "Edgegold" or "Topnotch". I've used Edgegold extensively and have found it superior to plywood for dimensional stability. That would be my 1st choice.
As long as you are going to all that work, you might as well saw the floor and run a trench for your dust collector ducting and wiring for your stationary machines.
My shop floor is concrete and is isolated from the exterior with rigid insulation. It acts as a thermal mass which helps to keep it warm in the winter and cool in the summer and works well. Our climate ranges from -10 f, to 110 f.
If cost was no object I'd like having a wood floor over the concrete also.
Bret
In contradiction to myself
I was at the "Y" tonight and noticed the one of their workout rooms has a floor made from varnished plywood. Looks great and seems to be holding up well. I think it's been there awhile.
After seeing that I would have to reconsider using OSB.
Bret
the cure, the cure
Curing time will vary based on the thickness of the slab. I've heard of at least a year being required for the typical slab, perhaps longer with thicker concrete.
The objective is to keep the space between the concrete and the wooden floor bone dry. I would think this would be particularly true if insulation material is placed in the dead space. Otherwise, it's an invitation for various nasty molds to start living in that space. Hence the suggestion of the additional moisture barrier, and ideally one that will seal around the fasteners used to secure the sleepers.
Depending on the amount of machine movement you anticipate, you might also want to double up on the flooring - OSB as the subfloor, and a harder material on top. Rolling heavy machines around on OSB will eventually break down the fibers.
the cure, the cure
[deleted - didn't notice the date on the original post]
Product called Advantec
Advantec sold in most lumber yards is a 3/4" sheet good used for sub flooring , is a 100% water proof, tongue and groove product. It is quite heavy and very stable. I layed it in my shop 10 yrs. ago and rolled on three coats of Fabulon poly. Everyone who comes into my shop marvels at the look of it and how flat/level the floor is. I believe you would have to weight each peice down as no sheet product is perfectly flat without assistance. It may take some time this way but the results will be worth it. It is a very dense product that even the heaviest machine will not dent it. Fabulon is sold in rental shops where you will find floor sanders. It has been around for many years, used where heavy traffic is expected.
A Cork floor..
A floor of cork is like a new bride...
will,
...a cork floor.
at one time i had the good fortune to work where the floor was cork and although i've not an inkling as to how this may compare to a new bride, it was very soft, easy on the feet and quiet.
eef
It all depends
It depends on whether it's the bride that's new or the marriage to her.
jam,
think you've corked it there!
jeez! is it ok to say that? this could get out of hand...
eef
Working through the Same Problem
I'm working through the same problem, so I'll tell you where I am. First, I think the 6 mil polyethylene sheet is a good idea. Some sites recommend a test. Tape a 2' X 2' sheet of 6 mil polyethylene to the floor and see if condensate forms on the sheet. That might be a good idea in some places, but here in Minnesota the air temperature at this time of year is likely to be higher than the temperature of the garage floor -- so I'm not sure that will work. So, I'm leaning toward using the 6 mil polyethylene vapor barrier. However, I have not yet checked code requirements.
One product that seems impressive is Dri-Core (see www.ronhazelton.com/archives/howto/insulating_floor_system.shtm and http://www.dricore.com). Dri-Core is a 23.5" X 23.5" tongue and groove ) OSB with a rubber or vinyl "nub pattern" substrate. This would permit some ventilation under the floor and might meet local building code requirements of ventilation to inhibit mold formation under the floor. It has excellent compressive strength properties; however it costs $1.25 per square foot and any overlay would increase the cost. Depending upon your application, it may produce adequate floor insulation.
The traditional method is to "nail" down sleepers with insulation between the sleepers and a subfloor above. This may result in mold formation -- again depending upon your application.
Another method, that looks most promising for me, is to first put down a vapor barrier. Then put down a layer of compressive strength foam insulation panels topped with a tongue and groove subfloor and finally a layer of finish floor. That would provide better insulation in my opinion, but I still have to talk with my local building code folks. It seems to me this could be laid down as a floating subfloor and it would require a finish floor too. But it probably provides better insulation than Dri-Core.
See www.garages.about.com/b/2008/11/24/insulating-a-garage-floor.htm for a comparison of the sleepers and subfloor over foam. This blog somehow make it difficult to paste in links. So I had to type them in. Hope I did not make any typos.
These are my thoughts. Good luck.
Lyptus, While I left my shop floor concrete, I did cover my family room slab with Oak Strip Flooring 30 years ago and it still is squeek free. I used a 22 caliber stud gun to shoot 4" spikes through 2x4 sleepers on 12" centers (over a vapor barrier) I cut rigid foam insulation to fit the voids then nailed 3/4 ply over the sleepers. I rolled 30# building felt butted edge to edge over the plywood and toe nailed my 7/8" oak flooring down. I did allow my slab to dry one year before I started.
At the gym where I work out, they have 3/4" composite rubber flooring that's dovetailed on the egdes to join the 4 foot squares together and the surface seems to be pretty rigid even when dropping heavy barbells on it.
Good luck on whatever you choose.
Plywood subfloor over concrete
Hi there Lyptus,
This all depends upon how well the original vapor barrier was installed. If you feel comfortable with the quality of the installation, then I'd install sleepers, set down on their face, not on edge, over some sill seal and attached them using a ramset or other powder-actuated nailer. Then go ahead and lay your plywood subfloor.
Good luck and happy building!
-Ed
The original vapor barrier was a 4mm polyethelene sheet. The contractor overlaid the vapor barrier with wire mesh and then poured the concrete. I'm not an expert on foundations so I'm not sure if 4mm is adequate by itself. After reading FW #160 on installing a hardwood floor over concrete, I just assumed one would need an additional vapor barrier on top of the concrete to reduce humidity in the shop and potential mold under the subfloor?
- Lyptus
Lyptus,
Let me for one add a vote for using a ram-set to fasten the sleepers to the concrete. Talk to your hardware store mgr. about the length of nail required for your sleeper material and the proper load charge. WEAR earmuffs!
As for flooring, I would give a thought to particle board. I like the surface and the durability. Give it a coat of poly.
As for the vapor barrier; I would eliminate it and provide an airspace at each end of the sleeper arrangement. With free airflow, I don't believe that you would have any condensation problem
Frosty
AZ method
Lyptus, sure a lot of different opinions. Here in AZ wood floors in houses are installed with a rolled roofing material on the concrete floor. This works as vapor barrier. A 3/4" TG Exterior rated plywood is laid on the not completely dry roofing material. It is then attached to the floor with the 1/4" roto hammer and double nail method, or the 3/16 drill and concrete screw. A hardwood system is laid over that. In your shop I would finish the ply with poly and call it ready to go. You should wait at least 30 days for the slab to cure.
If you go the sleeper route, 2by 4 glued and the foam in the middle. I would use Typar as the vapor barrier above that. It is controlled vapor material and resists tears as you install the sheet goods.
I would love a wood floor in my shop but the family car shares space....
AZMO
Ditto vapor barrier then ridged foam board then plywood
Lyptus:
Agewon has the best advice. Concrete cures rather than dries and will continue to take up and release moisture just like wood. The vapor barrier under the slab just reduces the amount of moisture entering the slab, it doesn't totally stop it. Personally I would use a glue down membrane barrier and not 6 mil plastic. The cheapest way to go is to use asphalt adhesive with 30 lb felt roofing underlayment. Overlap joints 4" with adhesive. There are also other types of membranes available. I suggest you go to a Lumber Liquidators or other flooring outlet to see what products they offer. Sleepers really aren't necessary, but you can use them if they make you more comfortable. The only advantage I see to sleepers is that they make replacing the floor easier in the distant future.
gdblake
shop floor
I have recently installed a plywood floor for my shop over concrete, not to say this is the best way, just how I have chosen to do it.
I laid down a plastic dimple membrane designed for use under floating floors, firm so as not to crush under load, about 3/8” thick, dimpled to allow air movement around under the floor but prevent condensation from entering the plywood. I pre painted the underside of the plywood with a sealer/primer type of product. The plywood I used was 5/8” sanded face T&G sheathing, the face has all voids filled and is sanded smooth, this is about 5.oo per sheet more than regular sheathing ply. I routed a slot in the ends of all sheets that butted together and installed a full with ¼” ply spline with some glue on all but ends. This kept all sheets flush without having to secure to floor, the entire floor floats on the membrane and slab and I left a small gap around the perimeter, covered with baseboard. I coated the plywood with several coats of poly floor finish. Is soft to walk on, easy to clean and with the weight of the machines, it’s not going anywhere.
It has truly been a great floor to work on, I screw jigs to it, and very forging to my chisels!
Cheers
Stuart
'Floating floor'
I'm impressed. Your solution seems very practical and the installation of the splines at the panel ends is a great idea. I'm jealous of your comfort.
I have a very cramped shop space* and thus everything is mobile: 16" bandsaw, combo jointer/planer and Unisaw. All roll very easily - on concrete - but I question if that would be the case on your 'comfort floor'. I guess I'll have to be careful about dropping chisels.
Frosty
* Small means efficient. I can reach most things just by turning around.
Rolling
Frosty,
I will bet this floor rolls as easy as any other. The poly coats will make that simple. The crush load of the rolling heavy tool on the wood is the same issue. Small little caster of steel with 2000 lbs on top will dent the wood. I would be willing to bet that your tools will work great and not crush the wood.
Now... the real issue.... do you have any frenz who want to help you install alllllll of those sheets of ply...!Ha.
Morgan
Frenz
Do I have any frenz?
First - move my machinery out of the shop, THEN lay the floor. Hard to say which is more time-consuming.
Where did you say you live?
Frosty
Tazmania..... haaha! Maybe Wotnow could pop over for you as well?
Morgan
Invite for a visit
Since both you and Wotnow are heading into the dead of winter, I issue an invitation to both of you to stop by sunny and warm Michigan sometime during the next few months of your 'seasonal distress". I believe you understand the conditions of the invite: beer and smiles from me; a little help from you.
Frosty
P.S. Do you suppose Wotnow would want to shave before he heads into hot weather?
I did this for a kitchen but shop floor is different
For a high end kitchen job built inisde a remodeled garage building with poured slab foor... the owner layed radiant floor tubing and then poured concrete over it. They were concerend about sweating or moisture issues. That was their concern. I suggested they roll out the sticky back ice and water shield on to the cleaned concrete slab. We then built a sleeper and plywood subfloor, and then wide pine over it. It has worked great. Sleepers were anchored.
For my shop floor I plan on doing it this way: 2x3 PT sleepers 16 inches on center on top of 6mil poly. 1.5 inch foam board between the sleeprs. Tongue and groove plywood subflooring screwed to the sleepers but not driven hard into the grooves. I do not plan on anchoring the sleepers to the concrete. On top of the ply subfloor tongue and groove variable width 1" inch oak boards screwed to the plywood and sleepers. Oak boards will be relieved underneath to help battle swellling and contraction. 2-4 full length 1/4 inch grooves on the underside about 1/3+ the thickness of the oak boards.
Should there be squeaks...well oh well. The weight of the benches and machines around the perimeter and in the center areas etc will be fine. And I can then easily remove the floor someday should I sell the house and shop and they want a 3-4 car garage without a wood floor. My thinking is very loose because it is just a shop floor and I want the floor to move and be somewhat soft for my lower back. It will be a lot better than the concrete floor dull ache tired syndrome. Plus I dropped a compass plane on the concrete and it broke in three piees. Arrrgh!
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