Given my previous data regarding moisture conditions and inappropriate installation of solid walnut plank flooring, can I reinstall the remilled planks by nailing only? I am extremely nervous that I could experience cupping again, even if I install the proper waterproofing and subfloor.
I understand what causes cupping, but I wonder if moisture can migrate up through the nails in the concrete from the subfloor, even with waterproofing. Someone at NWFA recommended gluing the subfloor to the concrete, but that seems risky...what if the plywood pops from pressure? What if the urethane doesn't hold due to expansion or general shifting of the plywood?

What if I use two layers of felt above the subfloor after applying the concrete adhesive, overlapping the edges 12", staggering the two layers, then nailing the walnut planks to the subfloor, no glue. Can I use 5/8" plywood, or does it have to be a minimum of 3/4" over concrete? Also, can someone tell me if tung oil or another non-urethane product can be applied to the surface which can be reapplied without sanding the surface again? I don't think I could survive the sanding and restaining process again!

EDITED By Administration:

Added

Posted: 21 Feb 2006 01:32 pm Post subject: Are 1/2" planks less stable than 3/4"

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I forgot to say that remilling the planks will reduce the thickness from 3/4" to 5/8" or 1/2". Will that make the reinstallation more unstable, or will there be no effect?

Only if you are face nailing.



You need to isolate the source of the moisture and fix it at the source. If for some reason you are still experiencing too much moisture you need to use a product like MVP. If the sub floor is already laid you can install it over the sub-floor but ideally it would be applied to the concrete.



No metal does not allow water vapor transmission, what can allow for it is the void the nail creates in the sub-floor. Go over each nail with some asphalt caulk to seal the hole.



Under normal conditions this should not be a concern, if it is then you need to look into a floating sub-floor.



Don’t overlap the seams you will cause ridges in your floor. Two layers will make it mushy.




If you are installing ¾ solid you need ¾ plywood. You can install on 5/8 at a minimum by ¾ is recommended. If you do the floating system it is two layers of ½.



If it has not been finished tung-oil can be reapplied.

thanks for your reply, kls. When you say face nailing, do you mean from the top of the plank, and not at an angle on the tongue portion?

There doesn't seem to be any obvious reason for the moisture in the concrete, it is present throughout the entire house. I will certainly apply the MVP. After it is set, do I glue down the plywood and then nail it every 12" or do I screw it down, as someone else in this forum had done? Should Bostik's Best be used over the MVP to glue down the plywood?
I don't want to use plastic over the subfloor, it's easier to work with roof felt. Do you feel one layer of 30# is sufficient? Should it be stapled down over the exterior grade plywood?

If you don't overlap the roof paper, then couldn't moisture penetrate the seams of the felt? I can visibly see the moisture penetrating the surface of the concrete where the seams of the visqueen meet under the slab, in the form of a salt build-up. That is why I thought overlapping the felt would be more waterproof, just like roofers apply it.

Also, is there a moisture test that should be performed over the MVP after it cures to determine if it is working, and if so, what should that reading be? What should the moisture content of the subfloor be?

You stated that 3/4" subfloor is best, would that apply to planks that are 5/8" thick also? I met with a hardwood floor miller, who will rip off the nail edges of the planks, and recut tongues and grooves, and will plane off the subfloor and urethane. I will probably end up with 4 1/2" planks that are between 1/2-5/8" thick, better than nothing.

Thanks for the help!

From the top down in three rows, you fill the nail holes with putty before finishing or leave them for a traditional look.




There has to be, have you had a expert come out and look at the moisture problem? Remedying the moisture issue will be the least expensive option.



If the moisture is a bad as you say it is I would highly suggest doing the following:

1. Use a traditional concrete sealer found at HD or Lowes.
2. Use several layers of 6 or thicker mill polyethylene film over the concrete.
3. Use the floating sub-floor system

a. Get ½ or ¾ sheets of plywood
b. Screw two layers together at a 90 degree angle.
c. Lay over film do not attach to the slab

4. Use 30# felt above non-overlapped used cutback mastic or tape to close the seams.

This is going to be your cheapest option for a high moisture slab and the most moisture resistant.

Without using the floating method, what is the next best approach? I only have 1 1/4" total for the finished floor, including subfloor and planks.

If I use MVP by Bostik directly on the slab, after it cures should I glue down the poly film with urethane glue, or just loosely lay it? Couldn't it bubble up if not glued? I am extremely afraid of one mistake, it seems that this wood floor business is an exact science.

With regard to your explanation of face nailing, I presume this is in addition to nailing the tongues? And when you say three rows of nails, is that per board? I only have about 4 1/2" of board width.

Since I plan to use the Waterlox tung oil, can it be applied to the back of the boards to aid in "waterproofing". I know there is no bullet proof system, but could this help or cause other problems?

Without using the floating method, what is the next best approach? I only have 1 1/4" total for the finished floor, including subfloor and planks.

If I use MVP by Bostik directly on the slab, after it cures should I glue down the poly film with urethane glue, or just loosely lay it? Couldn't it bubble up if not glued? I am extremely afraid of one mistake, it seems that this wood floor business is an exact science.

With regard to your explanation of face nailing, I presume this is in addition to nailing the tongues? And when you say three rows of nails, is that per board? I only have about 4 1/2" of board width.

Since I plan to use the Waterlox tung oil, can it be applied to the back of the boards to aid in "waterproofing". I know there is no bullet proof system, but could this help or cause other problems?

Use MVP then lay the poly-film and screw or nail the plywood to the slab through the film

4 1/2" you should be fine with just blind nailing it.

Polyurethane on the back of the boards would be better (and cheaper) at waterproofing than tung but yes you could use it.

Great suggestion, kls Have you tried poly on the back of planks with conditions such as mine with great success?

If you had my situation, would you even tackle wood flooring, or would you just scrap it and go the safe route with natural stone? I've seen horrible photos of cupped flooring on this website, even with normal moisture readings, and it seems erratic humidity changes can cause the "greenhouse effect", which was one of my diagnoses from an NWFA inspection. Who can predict what the future holds with RH factors

Either way I go, I will apply MVP to my slab. I'm just really scared that something else can go wrong down the line, and one more tear-out will cause me to flip out