HI,

I need expert advice, and this seems to be a good forum.

Over a year ago I had 850 sq. ft. of solid 6" American walnut installed in an existing home. The original floor was a glued-down engineered oak strip flooring over concrete, and was not only dated, but was drastically lower than the adjoining hall of 1 1/4", so I asked a flooring contractor if a floor could be installed on top of the existing floor. He should have screamed "NO", but instead he said it could be done if the engineered floor was stable.

By now you've guessed it. The end result was a disaster! The subfloor lifted and the planks cupped. Because the wood is so beautiful and was expensive, I plan to salvage what I can. Of course, the contractor was not a stand-up guy, and his license has been suspended from the Contractor's Board, but that doesn't help me any. So here are the details that I have learned from a professional inspection using a Tramex moisture meter:

Walnut Plank floor moisture reading is between 8.5%-14%
Sub-floor moisture reading is between 17-22%.
Relative humidity: 53%
Findings were: wood wasn't acclimated, no vapor retardant was in place, wood wasn't installed using 3/4" plywood subfloor.

Funny thing is I still have another room with the engineered floor still in place, no problems.

The question is this: If I am removing everything down to the concrete to start over and I use Bostick's MVP, apply another layer of 15# felt (or even 40# is better?), glue down exterior grade plywood 5/8 or 3/4", then apply another layer of felt or MVP over the plywood, can I reinstall the remilled walnut, or will I perhaps experience another problem, maybe not as severe, but what are my risks? Obviously there is moisture penetrating my foundation, it is consistent throughout my house. But there are no obvious leaks of any kind. A (6) mil vinyl vapor retarder was called out in the original house plans. This is the code in the Thousand Oaks area. By the way, the bare concrete moisture reading in one area was 4.5% and there is one 5' planter that is above grade adjacent to one corner of the room, but the rest is at grade level (90%) The moisture readings were done anywhere from 5' to 40' from the planter, the worst buckling was 30-35' away.

Can anyone give me any input? So far I have received a variety of differing opinions from experts, and every opinion differs as to the method of installation. Each floor manufacturer has its own specs, Bostick has another set of specs, and NWFA has its own, and they all seem to differ. I would like to follow the most conservative method, "overkill", if you will.

Thanks.

Probably the best way to avoid moisture from getting to your walnut flooring is to use a floating subfloor. After cleaning your floor and flatening it (leveling), consider using Taylor's Meta-Tek 2012 concrete sealer first, then after dry, install a layer of 8 mil polyethylene. Overlap seams by 12" and tape with packaging or duct tape. Then you lay (2) layers of 1/2" plywood in opposing directions to each other. I'm giving you a very simplified overview to see if you're interested in doing it this way. The plywood subfloor and the woof flooring on it are completely isolated from the slab. Unless it is done incorrectly, there is no way moisture can get to the flooring, at least from normal vapor transmission.

Thanks, Gary. I don't have more than 1 1/4" depth to work with, and I would like to use moisture retarder on the concrete, 5/8-3/4" plywood, roof felt and then the planks, nail down only. How would you attack this process?