Bathroom floor underlayment for sheet vinyl

Tenant didn't understand concept of shower curtain liner. Pulled up all underlayment to the wood subflooring of this 100 year old house, which is 4 inch wide wood flooring that is finished in the rest of the house. To lay on top of that, my 4'x 8'choices at Home Depot/Lowes seems to be :
1) 3/16" (true) thick Viroli (which I'm guessing is another mfg's name for Luan) @ $10
2) 3/16" (true) Hardwood Plywood (choice of oak or birch) @ $20
3) 1/4" (true) Plywood (I think it may have said sanded, but neither face seemed as smooth as choice 1 or 2.
Are any of these okay?
*Also, Black and Decker book's instructions for plywood underlayment(looks like 1/4" in photo, though they don't say) calls for 1/4" gaps between boards for expansion room. But it also says to then fill those gaps with patching compound (sanding afterwards). Stanley book calls for using penny nails as spacers between boards for what I'm guessing would be about 1/8", and then going back and filling any 1/4" gaps or larger with wood putty. Home Depot's book calls for 1/8" gaps, and then filling them with cement based floor patching compound. Doesn't filling the gaps negate the "expansion room"? Just curious how that works.
In another post I have a question about leveling.
Thanks.
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Hardibacker concrete unlerlayment 3' x 5' x 1/4" thick. Nail in the dimpled areas, use skim coat to cover the nail heads fill voids and level any irregularities. Install at least 4 mil plastic under the hardibacker and you should be good for about 20 years of service, even in a rental house.
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Hardibacker is more appropriate for ceramic tile.
What flooring are you putting down - vinyl?
Not sure I'm understanding your situation as far as the subflooring. Are you saying that the house has 4" wide planks as subfloor, with hardwood flooring on top, in the rest of the house. And that you've exposed the floor in the bath down to the plank subfloor? (Plank subfloor makes sense in a 100 year old house. I've even got it in my not quite 50 year old house).
(Somewhat of an aside: How far apart are the joists and what size are they? How big is the bathroom?)
You've got several choices, but I'd stay away from the oak or birch ply. Wasteful.
If you've got planking then hardwood flooring in the rest of the house, I'd lay down 3/4 plywood then your vinyl flooring. This assumes you can find 3/4" plywood in a smooth enough surface for vinyl, which may be difficult. If you can't find it, get something like 5/8" T&G subfloor ply and 1/4" luan on top of that. This should bring it near level with the flooring in the rest of the house. All seams should be staggered, on both layers and between layers.
Gaps are recommended between sheets of (the 5/8") subfloor ply, but I'd say that the 1/4" should be butted flush to serve as a smooth, gap free surface for the vinyl. The nails and other irregualrities should be filled, again to present a smooth surface for the vinyl. Otherwise, nails can translate thru the vinyl.
This is a fairly typical solution, but there are a number of variables that can affect it.
Renata
wrote:

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snipped-for-privacy@myrealbox.com (Renata) wrote in

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Yes and it works great under 12 x 12 vinyl or full glue down sheet stock. Be sure to skim coat the grooves and dimple out to a level surface.
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