I plan to install a 3/4 inch oak hardwood floor on existing cement slab floor.
Fortunately, I have almost a 2 inch rise to the door thresholds, so I can raise the level of the floor 1 1/2 inches.
My question is; can I first lay out a 3/4 inch plywood sub floor and glue it to the slab and then nail the hardwood floor to the plywood sheets?
Thanks for your input.
Replies
might consider 3/4 sleepers and in fill with 3/4 eztruded foam insulation and nail said floor to the sleepers. ?
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations.
Plywood is the way to go unless you need to insulate -- in which case go with Sphere.
This may help -- don't forget to check the moisture level of the slab.
IanDG
can't glue the plywood to concrete, won't hold......get 2" lead expansion sinks w/built-in hardened nail...... use hammer drill with proper size carbide bit for size sink used and go thru ply and into concrete deep enough to accomodate sink. hammer it down flush with surface of plywood so won't interfere w/wood install....at least 24 sinks a sheet, four across 4' width of plywood....any that don't seem to grab, or any movement, put another in close by......cheapest way to buy, look for a bulk pack of 25, 50 or more in hardware/fastener aisles......
IMPORTANT.......when nailing hardwood to plywood use 1 1/2" fasteners in the power nailer or staplegun. The longer 2" fasteners will penetrate beyond the bottom side of the ply hitting concrete and causing a lifting action.
lay down 8mil poly for vapor barrier on concrete
let plywood and hardwood acclimate on sleepers off of concrete in actual work area for a week or ten days before installation....open carton ends of flooring if boxed...check everything with moisture meter if have access to one
Thanks to ed2 and all the others for your input. All the information is valuable but also creates other questions that I would like to explore further.
My home is at grade in Southern Calif. Based on the input I have received it sounds like there maybe a couple of options for install: 1) ed2, hammer nail plywood to slab with vapor barrier (which will eliminate gluing) OR 2) HARDWOODGUY, glue (but this seem to indicate that keeping the plywood corners down was problematic.
Let me propose another idea which I would like to solicit your comments/suggestions on. Taking a cue from the popular floating Pergo floor concepts, I am thinking that if I edged glued the plywood sheets togther via GROOVE & SPLINE, on top of a 8 mil moisture barrier, I would then have a stable subfloor (that "floats"). I could then nail the 3/4 solid hardwood floor down.
Is my thinking too far out of the box? Appreciate hearing from you experience pros.
BAMPA
I wouldn't float one layer of ply.
However, if you could set two layers of ply, with the seams offset and the layers fastened to one another, then you could float the two layers over the vb and slab.
Your idea is very similar to a floating, insulated floor system used successfully in UK, except that there the concrete is first screeded over with a thin layer of fine dry sand to give a smooth surface, then 2" high-density foam slabs are laid down with the poly sheeting over that and finally the floating sub-floor with glued T&G joints.
IanDG
Hi Bampa-
Edge-gluing T&G plywood won't work on the same principle as floating floor products because the design/construction of the product is not with precision "floating" application in mind.
Floating floors are smaller and very stable in straight/flat and square construction from inception. Bear in mind that they must also be applied withing a +/- flatness of the substrate, or flexing/noise/breakage can result.
4x8 sheets of plywood are large and inherently unstable in regard to straightness, but that's ok, their normal usage doesn't require that pristine kind of construction. They're supposed to bridge framing members 16" or 24" o.c. and be nailed to schedule. ~~~Use FIR plywood, resists water and delamination better than pine.
Right off the pile at the lumber yard they always have some kind of curve to their plane which is taken in during nailing. Best example is heavy 3/4"ply which lends strength to the "wave", yet nailing down with air gun ringshank nails pulls the panel in tight.
Glue won't work for your application, and it precludes your use of a poly vapor barrier on the slab below the plywood, which is where it should be located. Use plenty of the lead sinks, and fasten any suspect areas with additional sinks to make the panel tight.
I used to rent Hilti hammer drills for this, but bought a Bosch "Bulldog" model hammer drill for $209.00, way better than the $40. a day rental plus the running around. Has a depth guage which the Hilti didn't have, saves time and drills by letting you drill to predetermined working depth but not beyond. Check website for Coastaltool in west Hartford,CT for these, also they have the Bosch hammer drill brill bits in all diameters, save about a dollar each.
Your best flooring widths for this application is 2 1/4" or 3 1/4". They will "adjust" and follow moderate imperfections in slab grade. Those imperfect grades to the floor stress the plywood, and that's why you want plenty of sinks to hold it permanently. Glue down of the ply will break free over time, floor will be noisy as hell, may fail over plywood seams.
Going wider than these flooring widths while using the shorter 1 1/2" nails or staples requires applying stripes of PL400 or similar subfloor adhesive under each course of flooring to keep the floor quiet and tight. In normal application onto adequate wood subfloor, 2" fasteners hold better than 1 1/2" nails. Even then, I glue anything 5" or wider. Be generous with the fasteners. A box of powernails which is supposed to do 1,000 sq.ft. of flooring on normal ply subfloor only gets 750 to 800 sq.ft. usage on my jobs. Space your end joints at least 8" away from each other in succesive courses to make floor strong and quiet. Do it right and don't have problems.....
For long life of floor, keep water drained away from house, keep gutters clean, and swale exterior landscape to push water flow away from foundation.
Hello ed2-
Thank you very much for all your help - your detailed explanations are very helpful and appreciated.
Before I go with the 3/4 ply nail down subfloor, I was curious about your thoughts on "Mongo's" suggestion: two layers of 3/8 or 1/2 ply with seams offset & screwed together & float over vb?
Bampa
i've been using sheets of 3/4" fir ply with good results, no problems. you do want to offset the seams as the panels get laid down, start with a 8' sheet one course, start with a 4' the next,etc.
don't see the point to using two layers, chance for noise, should be glued with pl400 or the like. The 3/4" panels are already there, integral strength...
be sure to use plenty of the sinks, run them flush with top of ply. check the hardware/fastener aisle in HD or lumber yard, look for bulk packs. was buying hilti brand at hd in their display area in 10pks, found 50ct. packs of red devil brand in the fastener aisle for a third the price. looked like they came from the same plant.
i hope that your slab is not below grade. The hardwood flooring institute says that the installation of solid hardwood below grade is a no-no. you must use an engineered product for this application.
carpenter in transition
Good point, Tim. I was recently asked to install some solid oak hardwood over a below-grade slab;(house was built into the side of a hill.) Flooring was by Bruce (Armstrong), and upon reading their instructions found that they said DO NOT install on any below-grade application!! They already had the wood (special-order)and could not return it! I turned down the job!
Edited 2/15/2004 2:12:36 PM ET by Duey
I've seen it done...glue plywood to concrete. Actually it was glued to 1/4" accoustical cork for sound control in a high rise building that won't allow mechanical fasteners. But it gets mighty expensive with the right adhesive. Curf cuts should be made on the back of the ply to allow for some flex. In this case the adhesive alone ran about $1.50 per square foot for both the cork and plywood install. Bostiks Best trowled at the rate of 30-35 S/F per gallon for ply and 80 S/F for the cork. Keeping some plywood corners down became somewhat of a problem.
You gotta know what you're doing in this case, Very flat subfloor needed...moisture testing a must if on grade. Basements? Not me.
Ken Fisher