Recommend me your proven methods, please. I will use 3/4 x 2-1/4 quarter/rift white oak, sanded after, then finished. My slab on grade is insulated underneath, and has hydronic heat within.
There is direct glue down, the Sika AcouBond glue down, and the plywood underlay method. But the ply technique has some differing and confusing methods when I read about it here and on other sites.
Everybody seems to say to cut the ply to either 4’x4′ or 2’x8′ pieces and sawkerf the back side with a 12×12 grid. The laydown should be in a staggered pattern.
What is better, 4×4 or 2×8?
As for getting the ply down, some say to bed it into mastic directly on the slab, while others say to lay down a poly film, bedded in mastic, and then ply over.
But I am unclear about the film deal (some sites say 15# felt is an OK film, too). Some advice is to bed the ply in mastic placed over the film, some say lay the ply directly on the film, no mastic.
What’s up here? What have you used with success?
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If you have the ability to accept the additional thickness...I lay one course of 3/4" plywood down on my slab. Cut to within 1/4"-3/8" of walls. Next course is glued and screwed to first, all joints offset. Flooring can then be installed as on wood subfloor. Rosin paper under flooring.
I am undecided about the poly. My experience is that it deteriorates in time even covered. CDX is a pretty decent vapour retarder, almost as good as poly. If your slab is prone to wicking moisture from the ground, I would consider using a cementous waterproofing on the slab, or at least a good concrete sealer rather than poly.
Unless your slab is terribly out of plane and level, cdx will be self leveling and flatning.
don't believe in mastics or glues.
I was told not to use asphalt felt under flooring that was on top of hydronic heat . That is unless you love the smell of asphalt in the morning noon and night.
I never use felt under any of my floors. Primarily because of the petroleum based impregnation; there is no justifiable reason to use felt when rosin paper works so well.
Over hydronic floors, what is the additional purpose of using felt? walk good
Are you an NWFA member? Felt is a moisture RETARDER, rosin paper is not. NWFA (which is the quasi-governing body of the industry) recommends felt paper, not rosin paper.Ditch
Rosin paper has been used for a longer time than felt for floor paper.
Felt is not a vapour retarder...it is breathable and will absorb moisture much like rosin paper. It will also retain that moisture much longer than rosin paper will.
paper under flooring over a subfloor was used to stop air infiltration and to act as a lubricant to minimize squeaks. Rosin paper works admirably for both purposes.
Subfloor plywood is a much better vapour barrier than felt and even 6 mil poly.
No I am not a member of NWFA. I had several attempts a few years ago, to find out why they no longer recommend rosin paper and never received a good answer. If they can not explain why, why should I change from a time honoured and proven technique?
I have been using rosin paper under my floors for a long time, over crawl spaces and basements, plywood and board sheathing and hydronic poured subfloors and never had a problem.walk good
So back to my question. What product is used to seal the concrete? Does the plywood go down in one layer?
My condition is a slab on compacted fill, above grade, in conditions of excellent drainage. Annual rainfall moderate. Radiant heat is within slab.
Here is what I got from a page at the Hardwood Council website. Lay 8-mil poly, then 5/8" plywood, then staple floor in place. No sealant or mastic is mentioned. Looks to me like the use of 1" staples will be required, so we don't penetrate the poly.
The WFMA information is somewhat ambiguous. Instructions say if moisture conditions are severe (they aren't), to prime the slab (they don't say with what) and apply cold cut-back mastic with a straightedge or fine-toothed trowel at 100 sf/gallon, then after at least 90 minutes, cover the slab with 4-6 mil poly, overlapping edges 4-6", and roll it or walk it 100%, and puncture any bubbles to release trapped air.
I guess that WMFA may be telling me that for my condition, I can just poly, plywood, and fasten finish flooring.
I want to get this straight, so I can properly instruct my flooring subcontractor in the RFQ.
There are many excellent sealants for concrete on the market. However very few of them seal the concrete from moisture travelling UP through the slab. You best solution, like you have done, is to minimize the moisture from under the slab with a good drainage plane to avoid water under the slab. The hydrostatic water pressure may be sufficient to penetrate ay sealer you may apply on the surface.
These are two sites that have sealants that may help you if that is the course you wish to take. Try to stay with a silicone or cementious based sealer to avoid the potential for smells etc. percolating thru your finished floor.
http://www.miraclesealants.com/
http://www.roancorp.com/sonneborn/sonnebornwaterproofing.html
I usually use 1" of HDPS board under my hydronic slabs on grade. These sheets are laid on tamped sand over gravel. Another layer of sand is placed over the foam boards before my tubing and concrete. This also helps to restrict moisture travel, but is not foolproof.
One course of plywood may be sufficient to nail your flooring into, but it has a tendency to cup and move unless you anchor it to your slab. That is why a two sheet staggered joint system is used. Glued and screwed together, the 2 sheets of 3/4"CDX form a rigid and usually flat subfloor surface that floats on the slab. Also the ouble sheet provides an excellent vapour barrier.
The problem with poly on the floor is that it soon developes so many punctures as to be useless. And I do not enjoy the prospect of some mastic slowly cooking and offgassing into my living space. It is bad enough to use the glue in the plywood. For that I use a urethane foam adhesive, which according to manufacturor's specs is stable and hypoallergenic.
walk good
We seal the slab 1st, lay down a membrane, then the sub floor.
Is the membrane 6 mil poly? Bedded in mastic? Mastic atop it to bed the subfloor ply? If mastic, what name brand?