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I've been watching some DIY guides on waterproofing a bathroom, for example: https://www.youtube.com/watch?v=TmrFUgI1C58

My question might be obvious but it's unclear to me; waterproofing protects the underlying substance but where does the water go once it reaches the waterproofing layer? e.g. if water gets through the top layer of vinyl or whatever is down, does it just evaporate over time or is the intent that it drains out somehow?

Basic question but not clear to me - any guidance appreciated.

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  • If water gets though the water proofing, then problems can start. The water proofing is to stop water from going though. If done right, any water will stay on top and find it's way to the drain or have a person wipe it up to prevent stains.
    – crip659
    Jan 25 at 23:57
  • Thanks for the response. That makes sense about the waterproofing system needing to be sound to prevent water going through. What I'm unclear about is if you put a layer on top of the waterproofing system (e.g. tiles), where does the water go if it gets stuck between the tiles and the waterproof system? Presumably its a limited amount and/or drains off as you say but that's still a bit unclear to me. Thanks
    – Keyvee
    Jan 26 at 0:06
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    You'll notice in that video that there's a floor drain near one corner of the room. That's where the water goes, even if it gets through the tile or whatever.
    – brhans
    Jan 26 at 0:31
  • The water usually won't get thru the tile unless it has cracked. The water can get into the crack, but wouldn't spread to wet another area because of the waterproof. Some of the water can be absorbed by the ceramic tile, some will re-emerge on the surface and flow down to the floor, the rest will be evaporated.
    – r13
    Jan 26 at 1:03
  • Ah ok, that makes sense :) Thanks all. @brhans, I'd missed the run off to the drain in the video but see what you mean. Thanks again!
    – Keyvee
    Jan 26 at 1:10

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In general, water shouldn't be getting through tile or linoleum or whatever's installed as the flooring in a room like this. However, some cracks and pores might eventually come to exist, which is why waterproofing is necessary for the subfloor. Where it goes depends on what's going on in the room: if the flooring is sloped towards a drain, it'll go down towards the drain. In the video you linked, the baseboard area is waterproofed, and there is a drain in the center of the room, so if you had a large amount of water pouring in, that's where the vast majority of it would go.

Usually, though, we are talking about small amounts of water here. If a few droplets manage to get through some discontinuity in the grout or whatever and don't make it all the way to the drain, they'll eventually evaporate, and the water vapor will come out the same way the water got in (if water can get through cracks in a floor, so can air). Generally speaking, water doesn't stick around forever if it's exposed to air -- if you leave a glass of water on the counter and leave for a vacation, for example, you may well find that it's completely empty when you get back. An exception is if it manages to seep its way into a porous material, in which case it can stick around for quite some time.

Of course, "eventually" is relative. If you have a big crack in your bathroom tile, and it's right near the place you step out of the shower every day, it's possible that there will be some persistent wetness between the tile and the waterproofing, which could get to smelling rather bad, but it's not like it's going to stay there forever (if it got to be really awful you could just turn on a fan and open the windows or run a dehumidifier in the room).

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    Excellent write up, thank you! I've watched a number of tutorials that do a thorough job of how to waterproof an area but weren't explicit that its the last line of defence, with the flooring material designed to keep out the majority of water. It's obvious now :) Thanks again. Cheers
    – Keyvee
    Jan 26 at 10:58

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