Mahogany subfloor

[hope9010]

To install a luxury vinyl tile (LVT) floor on top of an existing old slab-on-grade basement floor, in a room that is a multi-purpose social hall (dances, assembly, dining, gym, etc.), the flooring contractor is proposing installing about a 1/4" thick "mahogany" subfloor anchored to the concrete, to level any irregularities that there may be in the existing surface. Then he would adhere the LVT on top of the mahogany subfloor, using a water resistnt urethane adhesive.

My questions are:

1. How resistant is "mahogany" to moisture and rot? There was a basement flood two years ago due to a broken water main and the soil under the slab-on-grade may have become saturated by that and not fully dried out yet.

2. If we were to have another flood due to say a plumbing break in this 50 year old building, would the magonay subfloor have to be removed?

3. Should we be measuring the current internal RH in the concrete slab, by installing 2 or 3 drilled-in RH sensors in the concrete slab to measure the internal RH, just in case there is moisture rising from the soil, or would it suffice to only use a surface "moisture meter" which is touched to the surface of the slab-on-grade and measures surface moisture only but not internal RH of the concrete?

Please note that I realize that the concrete after 45 years would be expected to have dried out, but the flood that covered the basement with 4" of water two years ago may have saturated the subsoil and it may not have yet dried out. The polyethylene under the slab-on-grade can be expected to have many punctures and not form a real vapour barrier.

 

[boo1]

In my area the 1/4" thick "mahogany" ar not true mahoganies. One of the substitutes is Lauan, which is marketed in the United States as Philippine mahogany.

Water resistance should be a function of the glue system the plywood uses, rot resistance is from the actual species of wood. Using 1/4" wood subfloor in a basement on-grade application, has risk from the plywood not being stable and rot.

 

[hope9010]

boo1;

Thanks for the response. The factors that you mention (wood rot; glue) are what I am concerned about.
In what area of the U.S. are you located?
Do you know if true mahogany subflooring has good rot resistance, or where I might find information on that?
Do you know if the Philipine mahogany subflooring has good rot resistance or where I might find information on that?

Thanks again for your help.

 

[boo1]

im located in SE USA. True mahogany is very good for rot resistance, but your core layers would still be unidentified. The imported 1/4" typically dont have APA rating stamp to give you the application rating or underlayment grade. Is it a marine, construction, or finish grade?

1/4" plywood overlays typically are used over Wood Subfloors not for Concrete Subfloors in a basement. You dont know how durable it will be. Contact the manufacture of the LVT floor system or look on their wed site for application guides. I bet they will not warranty the application.

Could you smooth by applying a cementious overlay such as patching or leveling non-shrinking water resistant Portland cement patching compound?

Forest Products Lab has info on woods

http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id=100&header_id=p

 

[jayrod12]

That was my first though boo. why not just pour a leveller over the existing concrete and then applying the lvt directly to that

 

[boo1]

agree

 

[a2mfk]

DO NOT DO IT, unless you like lawsuits. I have investigated many flooring failures due to the installation of one flooring type over another, specifically a less permeable material over another, as it creates an unintentional moisture barrier. I have specifically seen vinyl installed over a wood subfloor or old hardwood flooring and the results were bad- wood swell, buckling, wood rot.

The best option, and probably cheaper, is to grind down any really uneven spots and then use a cementitious self-leveling compound (as jayrod said).

I am also surprised that anyone would suggest mahogany for anything other than decorative work or furniture, due to the expense. When wood is used as a subfloor, it is usually plywood.