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I have a concrete bathroom floor where I want to install new fully waterproof vinyl at a finished height of 1/2 inch to bring it level with the hall floor and make it feel less like walking directly on concrete which previously had very thin vinyl(?) with a papery backing glued directly to the subfloor (see pictures). I'm scraping the old vinyl up and starting fresh.

Here's more details:

  • built in 1988 and located in the DC metro area
  • the bathroom is approximately 6' x 8'
  • this is ground level with earth on one side of the level (built into a hill)
  • the subfloor is smooth concrete
  • the slab likely touches ground but I expect it has its own moisture barrier
  • the slab comes up a few inches above walk-out level
  • the hall flooring, also on concrete and adjacent to the bathroom, is bamboo planks (I'll confirm this) with thin underlayment of what looks like a thin light green foamy/felty material. (I'll add pictures).
  • the previous bathroom flooring is shown in the pictures: some thin vinyl-ish material with paper backing, glued directly to the concrete subfloor.

My original plan was these layers, bottom up:

  • cleaned up concrete subfloor (scrape away glue and fill minor divots)
  • moisture barrier (breathable?)
  • treated kiln-dried plywood (maybe 1/4" or 3/8") screwed into the concrete
  • maybe some padding so it's not as hard as plywood?
  • vinyl sheet (glued down)

Does this sound proper to you? What should the moisture barrier be, should it be breathable? Is there a universe where I get away without screwing into concrete? Any warnings?

Thank you for your insight!

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    What is under the concrete sub floor? Is it on the ground or a floor that is above the ground/some space between floor and ground?
    – crip659
    Feb 22 at 23:08
  • @crip659 I've updated my answer to include more details. Thanks!
    – xtratic
    Feb 23 at 13:59

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Why build the bath like it was 1982? Use new technology.

An LVP/ LVT rated underlayment of 4 mm and a finished LVP or LVT ( example of LVT) of 7.5mm will get you 11.5mm or .449 inches.

The concrete does not have to be perfectly clean as minor imperfections that would show through the sheet vinyl will not be an issue with LVP. No other plywood is needed as well. There is nothing to screw or glue Just a better way to do a floor.

I have used these products in a few bathrooms myself and had no problems. The flooring has been down for 5 years now. I do recommend sealing around the toilet flange with polyurethane caulk to prevent any leaks from getting under the flooring.

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  • Some people like vinyl (they're weird, but they exist). Others like actual, genuine linoleum (it's naturally antibiotic - that's why it's used in hospitals).
    – FreeMan
    Feb 23 at 14:24
  • I think I will go with this option. Thank you!
    – xtratic
    Feb 23 at 15:46

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