Greetings,

I am installing 3/4" solid hardwood over a 3/4" plywood subfloor (will staple floor down). On half of the installation area, there was glued-down parquet thathas been removed. While removing the parquet, the first ply of the plywood subfloor has been torn off in many places big and small, creating a motley pattern of gaps in the subfloor.

My question is how do I best fill these holes so the subfloor is flat? Is there a leveling compound appropriate for nail-down installation (product name appreciated)? Do I have to cover with another layer of plywood?

Any recommendations ares most welcome.

Thanks in advance.

Craig

In these situations, I have found it was easier/faster to install 3/8" CDX plywood over the whole thing. I've tried the sanding/filling route but it was tedious and labor intensive. More plywood will cost more than repairing the subfloors but your choice. Most leveling products I am aware of do not accept nailing into very well. Cracking seems to be the issue.

Thanks Gary. Appreciate your advice.

I have been having a tough time getting a straight answer from my local flooring 'experts' on leveling compound. Some say it's not a problem with staples as they're too small to cause significant cracking. Others simply don't know. I suspect, however, that you're on the money with the cracking issue.

I have read elsewhere that there is leveling compound that has fibres in it to prevent the cracking you speak of. If there were an appropriate compound, it would be preferrable as, like you say, putting down plywood would be much more expensive.

Anyone else care to pitch in on this issue?

Thanks again for your help.

Craig

If it is poured no more then a 3/16" Ardex SD-F will not crack out with a fine 18 gauge staple. It has a lot of latex in the mix and is very resilient, like rubbercrete.

If you get it thick, a staple will bend and not puncture it cleanly


Mapei has the stuff with fiberglass reinforcement, but that stuff is very sandy, and would need a skimcoat of planiPatch, to encapsulate the sand.

Looks like 3/8" plywood it is. I don't want to take a chance with floor leveling compounds.

Thanks again to you both for your wise counsel.

??? Just cut out the damaged part and replace it with new 3/4. It can be CDX. Just cut it at the joist nearest the wall, not at the wall line. It will be a hell of a lot faster and cheaper.

Thanks Chuck,

That makes sense to me. That way I can also see the 'interesting' wiring configuration under the floor, which I haven't dared touch because the ceiling below is finished.

You guys are fantastic! Really. Thanks to you all.

Plywood subflooring is typically T&Ged. If using a CDX non-T&Ged plywood, then blocking must be added whenever there is a joint to support the panels. Failure to do so will result in excessive deflection, movement and flooring failure. I typically do not recommend homeowners who are not contractors to perform structural repairs to their homes. It isn't that this is a super skilled job, it's just important that it is done correctly. I have seen lots of carpenters do crappy subfloor patch/repairs.

Plywood under 3/4 hardwood needn't be t&g, Gary. You should know that, man.


Ever heard of installing over screeds?

Screed systems are typically 2x4 pressure treated boards laid flat and spaced 12" oc, which leaves about a 10" span between the screeds. Plywood subfloors are typically spanned 16" oc. Should a joint in the wood flooring land on an unsupported seam in that subfloor, excessive deflection can occur. Best not to take chances and use either T&G plywood or block the joints under the subflooring. I guess that's why my subfloors are rock solid and never squeek, whereas the majority of them I run across done by others need lots of repairs.
https://www.nofma.org/Portals/0/Publica ... 010_04.pdf

Now you went and made me angry, Gary.

Why did you make me read that? O well, it presents an opportunity for clarification, so I thank you for the link.

Here is the deal: The term deflection is used to describe the behavior of the framing members, not the underlayment. The term used to describe the movement of underlayment panels between the framing members is "curvature". In almost all cases, curvature is a non issue with 3/4in flooring. That is why Mickey never referenced it in his article. I can elaborate if you would like, but there really isn't all that much to say about it.

Thicker plywood will indeed ameliorate a deflection prob, but that is a separate discussion. (I am in the midst of an argument with some supposed tile savant and his butt-kissing harem at another board concerning the efficacy of using stiffer underlayment as a way of alleviating deflection. They actually claim that adding plywood does nothing to stiffen a floor.)

Be well,
CHU

From the Oxford American Dictionary
Deflect: to turn or cause to turn aside. So it seems that the term "deflection" as used to describe flexing of floor joists, is somewhat misleading, according to this dictionary's definition.

Well, they're wrong! Just as adding blocking between joists aids in reducing "deflection", so does loading the subfloor with thicker (stiffer) subflooring. And while it may seem ok not to use T&G plywood, the small cost and effort pays bigger dividends. Also, what if the wood floor was removed down the road, for whatever reason, and another flooring type was desired. Would it not be preferable to have the proper subflooring in place to begin with?

The house is about 50-60 years old and the subfloor is currently regular old plywood--no T&G.

By blocking, I assume you mean perpendicularily spanning the floor joist at the point where two plywood panels meet so you can marry the plywood edges to a support. If not, please explain.

As it sits now, there is no 'blocking' or any other kind of support at the seams that run perpendicular to the joists. The joists are 2"x10" with 16" centers.

Does that change the equation at all?

That would not pass code in CA. in any municipality. But if it's ok where you are, carry on with Chuck's suggestion of replacement. Framing techniques and requirements are different throughout this country, as I'm finding out.

Muchos gracias to you all.