I have a bathroom with a wooden floor - not floorboards, but solid sheets of water-treated chipboard. It's an old house, ~90yrs or so, and we're renovating it. A lot of the work has been done by competent professionals, a little of it has been done by me.

As part of the bathroom renovation we had a shower installed. A carpenter erected a wall at the end of the bath to form a cubical in the corner of the room, this wall is made from a single sheet of chipboard sandwiched between four sheets of water-treated plasterboard. Following this, a plumber fitted the shower tray (porcelain), the pipe work and the shower itself.

I have then tiled the shower cubical (but alas, not with flexible adhesive), grouted it and siliconed between the tray and the tiles. The problem is the shower leaks. It's not much, but it's probably damaging the wall and the floor slowly.

At first I just used regular grout and silicone. It leaked. I then got some flexible silicone, removed the original silicone and re did it. It still leaked. I then got some flexible grout, scraped out all the original grout and re-grouted it. It still leaks...

I don't know what else I can do, I don't particularly relish the thought of regrouting and re-siliconing once again, and I'm not even sure that if I did it would fix the problem.

Does anyone have any experience of this situation with a wooden-floored bathroom. I'm sure there is a slight movement when stood in the shower. The floor is a new floor by the way, laid by the carpenter as part of the renovation.


Hi, thanks for the comments, ok:

@BMitch - No, I didn't install a membrane. Wish I had known about these 9 months ago!

@HerrBag - We've got the drain pipe exposed, it's definitely not this. We did fit the green plasterboard yes. The water is coming from from the edges of the porcelain base, it's definitely like it is seeping through the grout and running down the wall behind the tiles. i'll look out for grout sealer or some other waterproof agent I can apply to the grout. Thanks!

#Edit 2 It's almost 10 years later, but the question seems to be getting some traffic so I'll provide another update.

After the last edit, I bought some grout sealer, the brand was HG, had to get it from Germany if I recall, but was supposed to be very good. I painstaking applied it over all of the grout in the shower with a tiny paint brush, but sadly, it made no difference at all. I resigned myself to the fact that I had a leaking shower and we just sort of perservered with it for another four or five years. I moved on to other projects in other parts of the house, and we just mopped up spills after each shower and tried to keep it as dry as possible.

Eventually we had a whole new bathroom fitted by a proper fitter and that was finally the end of the leaking shower.

  • 2
    Did you install a waterproof membrane behind the tiles? Grout isn't waterproof and will leak.
    – BMitch
    Commented Jul 9, 2013 at 21:26
  • @bmitch grout sealer will help the vertical surfaces
    – HerrBag
    Commented Jul 9, 2013 at 22:39
  • 1
    A diagnostic to try: eliminate drain as issue: fill only pan, keep walls dry. Use hose if necessary.
    – HerrBag
    Commented Jul 9, 2013 at 22:43
  • 1
    Is "water treated" plasterboard (aka green board) directly under tile?
    – HerrBag
    Commented Jul 9, 2013 at 22:45
  • Where do you see the leak?
    – HerrBag
    Commented Jul 9, 2013 at 22:47

2 Answers 2


I'm very sorry to say this but you're going to have to remove all the tiles and start over. You will never been able to prevent this from leaking fully.

It may also mean removing and replacing the backing as well.

The critical step you missed was the waterproofing membrane that goes under the tiles and in and over the drain pipe. The tiles don't stop the water at all but are for aesthetics only (and to protect the water proofing). What makes the shower water tight is a sturdy backing covered with a water proofing membrane like liquid flash (one I used) when I did my tile shower. http://www.constructionchemicals.com.au/products/waterproofing-membranes/

But there are many different brands. They are a paint on product and very easy to install.

Don't expect your tiles to be waterproof. At best they are only splash resistant. Water goes right through the grout and can also enter around the side of the tile where the grout is. Porcelain tiles aren't quite as porous as ceramic, but most wall tiles are ceramic because they are a lot lighter. These tiles act like a wick and just draw the water through to the back of them. If you don't fix this you could be in for some serious mould issues down the track.

Unfortunately there is no simple fix to this but to start over. I would not recommend just trying to seal it. It's like covering up rotten wood with paint, it won't last and won't fix the problem long term. Although you've got water resistant plasterboard. It won't last long term. These plasterboards are just designed to repel water to keep it out of the gypsum they are made of, not designed to be constantly wet.

Interesting construction that your builder used water treated plasterboard + chipboard for the construction. 6mm or 1/4 in thick concrete based tile & slate underlay board + waterproofing membrane is all you would have needed. I wouldn't recommend tile on plasterboard at all. Even with the layers that he has. It's not as strong.

Since I know how much work goes into these DIY tile showers I will say this. If you feel overwhelmed, call in an expert. They will have the job done in a week and you'll be able to move on with life. But if you're up for the challenge and want to learn to do it right this time, then dive in and go for it!

  • Ok thanks Matt, I was hoping it wouldn't be the case, but the explanation makes perfect sense. I think I will probably have to call in an expert on this - I've spent time doing the tiling in the first place, as well as grouting several times and adding the silicone several times. I don't think I can face starting it all over again! Thanks for the answer :)
    – danwellman
    Commented Jul 11, 2013 at 13:21
  • I know how you feel. I've made some major mistakes in my learning too. So it pays to get lots of advice first. These Q&A websites were not around when I did my shower and it was by pure chance I learned about the need to use a water proofing membrane.
    – hookenz
    Commented Jul 11, 2013 at 21:32
  • I don't have such an excuse unfortunately - not only was this site around, I was already a member!
    – danwellman
    Commented Jul 12, 2013 at 12:39
  • @Matt, would it help to install plastic shower walls without removing the tiles?
    – z-boss
    Commented Mar 19, 2014 at 14:28

Try putting the silicone on whilst you are in the shower tray. Your weight will bring the tray down to the level it will be when in use. Loads of people seem to want such long showers these days (I don't understand it I just soap myself clean and go) and this puts such extreme severe strain on buildings. Also make sure the room is well ventilated.

  • How does the length of time you're in the shower affect the strain on the building?
    – Niall C.
    Commented Oct 14, 2014 at 15:09

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