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Hey all,
I’ve put together some ideas from all of the posts I got from my hardwood flooring over a concrete slab question a while back. Of course, thanks for all the great replies. Here is a profile of how I think I’ll do it.
12mm wood flooring
30 lb. felt
3/4″ ply t-nailed to slab
30 lb. felt
slab
Any thoughts on that?
I would have liked to had two layers of ply but the added height will disrupt all the areas where the wood will meet floor tile. With this profile its a small transition but add another 3/4″ and it not realistic as it would become a step.
My primary concern is that this subfloor thickness is not enough depth for the floor nailer. I know the Porta Nailer nails are 2″ and even at the angle they are driven, they still may bottom out on the concrete. Not sure about other nailers such as Bostitch??? I could add a layer of 1/4″ ply if that would help as that wouldn’t make any transitions too high.
As always, thanks for any input. This is my first “flooring over concrete” job so I’m sweating all the details.
Mike
Replies
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Michael, Could you use 2 sheets of 1/2cdx instead of the 3/4cdx? You could eliminate the fastening to the slab and just float the cross-hatched cdx. I use the "arm-strong" floor nailer, a Powernailer by brand. It will shoot 1-1/2" which will secure your flooring without over penetration.
30# felt is probably over-kill as under floor paper. 15# felt is fine, my personal reccomendation would be rosin paper.
With the two sheets of cdx, just glue and screw the sheets together.
walk good
david
*David, Hmmm? You got me thinking now... Do you ever have trouble with buckling or the two sheetings of 1/2" flexingwarping? By that I mean a bounce when the final floor is installed later. I do like the idea of floating them and not having to nail thru the paper into the slab as all those holes are more sources of moisture intrusion. Maybe I'll just go with 15# between the ply and the slab and rosin between the ply and the flooring. The slab always seems "moist" to me hence my desire to use felt paper.Thanks.Mike
*I have a similar situation, a concrete slab. Somewhere, I believe this magazine or one of the TV shows, I saw something about floating wood floors where you glue the pieces together and it isn't anchored to the slab. Anyone else know anything about this, or tried it?Also, just curious, have you considered concrete stain?
*Steve, I believe you can only use the full-floating aspect with engineered flooring. (Someone correct me if I'm wrong of course). The engineered floors can be made to have the pieces adhered and not attached to the subfloor as they don't need to "move" like solid wood flooring does. Sold wood flooring will buckle if they are glued together and not allowed to expand and contract independent of the piece adjacent to it. (Once again, correct if I misspeak). Hadn't thought of the stain option...I guess its just too "modern" for the job?Mike
*Michael, Depending on your inherent slab moisture, two 1/2" may have some buckling. It is not my ideal choice but given the heigth limitation you have it would increase your overal thickness by 1/8" over a single sheet of 3/4"cdx. Also I think you would have less problems with buckling than a single sheet of 3/4" even nailed to the floor. Constant movement on the floor can loosing concrete fasteners.If you could give yourself another 1/4" then by all means use 3/4"cdx cross-hatched with 1/2" and your potentoial problems are further reduced.#0# felt is not a good moisture barrier. As it becomes wet, it's permiabilty increases. If moisture in the slab is a concern, I would reccomend a good concrete sealer like THoro-Seal applied before the plywood direct to the slab. Plywood in itself is an excellent moisture barrier, so you will have minimal moisture working through to your flooring.Staining might be a good option. There are several excellent stains available that can change the appearence of concrete and make it look more natural. Also you could saw grout lines into slab before staining , acid etch the floor, then stain. When dry come back and grout your score-lines as tile. Looks great.walk gooddavid
*David, I had heard that about felt when in constant contact with concrete. I had considered using a rubber membrane style covering but that that was overkill as well as overcost$$$. Is Thoro-Seal a penetrating sealant or does it build up a membrane style coating like the one by Custom products that you use for sealing under showers, tubs, etc? Am I correct in assuming that a layer of felt between the ply and the flooring itself is still a good measure to eliminate squeaks?Thanks.Mike
*Mike, The thoro-seal I have used is a brush on cement based waterproofing used on foundation walls. It is only one of many products available. It is not a penetrating sealer and I suggest it because I know it works and with a floor over it will not wear down. But it is not your only choice.15# felt has long been used as under floor paper to help eliminate squeaks, and in the days of board subfloor sheathing as a wind/ air infiltration barrier. Red rosin is another choice which I prefer as it has no petrochemical saturants in it. It works as well as felt. There are several other products as well which I have not used, being satisfied with the rosin paper. Take your pickwalk gooddavid
*Michael, I have installed several free-floating 7/8 inch solid oak pre-finished floors over existing concrete slabs. The product I was most satisfied with is called Junckers (pronounced "Yunkers"). It is a british flooring availible probably most anywhere in the states that floats free and clips together with metal clips. It installs over a 1/8 inch thick felt backed moisture barrier that you tape to the slab with duct tape. There is a required gap at walls/thresholds for expansion that I think is 1/4" per 10' of floor. The felt pad takes up some discrepancy, but I have also used 1/8" tempered board for shims. It installs quicker than nail down floors and their pre-finished product comes out really flat. I think that thoro-sealing the slab is essential, especially if it's below grade. I lost Junckers phone # but they probably have a website. -Tony S.
I tend to like the concept of the floating plywood subfloor when installing 3/4" flooring. My concerns are in floor height transitions between 3/4" flooring and ceramic tile in adjacent rooms on a concrete slab. Are the edges of different adjoining surfaces going to create trip hazards? What strategies are there out there if one really wants to but 3/4" flooring over a slab when he's going to but it up against ceramic tile?
Edited 5/2/2008 7:53 pm ET by ramsrime
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Hey all,
I've put together some ideas from all of the posts I got from my hardwood flooring over a concrete slab question a while back. Of course, thanks for all the great replies. Here is a profile of how I think I'll do it.
12mm wood flooring
30 lb. felt
3/4" ply t-nailed to slab
30 lb. felt
slab
Any thoughts on that?
I would have liked to had two layers of ply but the added height will disrupt all the areas where the wood will meet floor tile. With this profile its a small transition but add another 3/4" and it not realistic as it would become a step.
My primary concern is that this subfloor thickness is not enough depth for the floor nailer. I know the Porta Nailer nails are 2" and even at the angle they are driven, they still may bottom out on the concrete. Not sure about other nailers such as Bostitch??? I could add a layer of 1/4" ply if that would help as that wouldn't make any transitions too high.
As always, thanks for any input. This is my first "flooring over concrete" job so I'm sweating all the details.
Mike
there are flooting floors that have metal clips that hold them together on the back side. Used on floors for arobics etc. Put a foam or rubber thermal / vapour break underneath