I want to convert a 1st floor room into a bathroom, retaining the original wooden floorboards. There will be no shower, just a bath in the room. What needs to be taken into consideration with regards to waterproofing the floor to prevent splashes, spillages and kiddie bath time from ruining the ceiling below?

  • 1
    note that kids taking baths can cause WAY more water on a bathroom floor than a shower in heavy use.
    – DMoore
    Jan 13, 2015 at 21:32

1 Answer 1


You could sand down the floors, and refinish them with oil based stain and polyurethane. That should be enough protection to keep the floors from rotting. You could do what they did in the old days and put towels down around the tub and wipe up spills immediately. Standing water will leak through the cracks between the floorboards.

You could also good clear polyurethane caulk meant for bathrooms and fill the gaps between the boards around the wet areas, or on the entire floor. This should prevent water from seeping to the room below.

  • Am I correct in assuming that it's a lost cause to try put down a waterproof layer below the boards - as it will need to drain somewhere and will likely cause water to collect against the undersides of the boards causing rotting issues?
    – Andrew
    Jan 14, 2015 at 9:19
  • @Andrew you would most likely destroy the old boards if you tried to remove them. Jan 14, 2015 at 12:36
  • I thought the same, but we've been lifting in other rooms and they've come up surprisingly easily and they're in great shape - which is why we're considering leaving them intact in the bathroom (originally we were just going to tile). the thought process continues...
    – Andrew
    Jan 14, 2015 at 12:46
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    If you lifted the boards and installed a membrane below it and re-installed them, then the membrane would be destroyed when the floor was nailed back on. You would also need to install a subfloor, and then waterproof that. Doing so would most likely change the height of the finished floor. Then you would have issues with floor heights not matching to the next room. Membranes are only useful on tile floors since they are 'glued' on by the thinset and don't use mechanical fasteners. Jan 14, 2015 at 13:44

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