Leaking tiled shower enclosure

Help please! Last week I installed a new shower in my daughter’s flat and it is leaking, I think through the tiled walls. I built the walls of 12mm WBP exterior ply sealed with (one) coat of oil-based primer, as suggested on the tile-cement tub. The cement is waterproof and specifically claims to be suitable for tiling over wood. The grout is waterproof and mould resistant, claimed to be suitable for showers.
I grouted using a rubber float, pressing it well in and smoothing the joints with my finger (I never seem to have a handy implement for this). The cement was buttered all over on the back of each tile (rather than on the wall) and lightly ridged i.e. a continuous layer of cement. Perhaps I didn’t mix the grout quite as stiff as the 4:1 cement/water ratio recommended but not too far off and it certainly wasn’t sloppy. The tiles are 200 x 250 mm but with a border tile at mid-level, a mosaic of natural stone (marble or similar) sealed with Stain Stop (3 coats, 1 before grouting and 2 after). I took the opportunity to apply Stain Stop to all the grout as a further measure (I hoped) against mould and water penetration.
How might the tiling have failed and how can it be fixed without starting from scratch? If absolutely necessary I would tile over the current tiles but I’m not keen on that solution.
Nick

The grout will be water resistant and not water proof - there's a difference. It just means that the grout won't break down when it gets wet...... not that it won't let water through.
The easiest (and most probable reason is that it's a silicone seal that's failed or it's a plumbing problem..probably the trap).

Thanks for the suggestions. I can still access the trap beneath the tray and can feel no wet from there. I will double check the connections to the shower mixer by coming through the (stud) wall from behind, but I did check connections before fitting the ply and thought they were OK. The silicone seems to be applied OK to the wall/tray and corner joint and to the outside of the enclosure frame, as recommended). Everything was new and cleaned with meths before applying the sealant, which does not appear to be lifting anywhere.
I remember having a similar problem in the shower in my own home. Having applied lashings of silicone to no effect and inspecting through the walls from behind I eventually fitted a polythene "tent" inside the cubicle and that stopped the problem- I could see no apparent fault with the tiles or grout. So I "tiled over" and that provided a permanent cure until I eventually refitted the entire bathroom. This is why I suspected I may have a similar problem with grouting in this case.
Might "water resistant" grout leak, and why? If I attempted to remove/replace the grout how could I ensure it was better (and what is the best method of removing the grout)?
Hope you can suggest answers as I'm not confident that the plumbing or sealant are problems.

Have a read of this thread //www.diynot.com/forums/viewtopic.php?t=22291&highlight=shower+tray+leaking

When you say a leak, how much water are we talking about? A drop or a river?
Where can you see the evidence of a leak? Downstairs or under the tray?

If the leak is only small and you can't really detect where it's coming from then you may be correct in thinking that the water is getting behind the tiles. If this is the case, I suggest you probably have movement in the walls. Maybe cause by the weight in the shower tray pulling at the wall when you get in it. Might have caused a crack in the grout.
I've seen shower cubicles before where there's a whole tiled section at the bottom that move independantly of the rest of the walls. This was were the plasterboard joint was.
You need to make sure that the shower tray is very firmly fixed in place so that there's no movement when you get in it. Is it a cheapo tray that flexes with your weight?
If the grout was 100% then you shouldn't really get water through it - it might let water soak into it (a bit like a sponge), but the amount of water a domestic shower is exposed to shouldn't really cause a problem.
However, that said, if you still feel that that's where your problem lies then regrout it. Not a fun task. You need to scrape out the old grout using one of these http://www.screwfix.com/app/sfd/sea...TF-8&q=grout+remover&pn=1&pd=1&pi=1&cn=1&cd=1 to a resonable depth to provide a key for the new grout. Then once grouted re-seal the grout again. By the way, if you get that tool, it might come with 2 blades side by side, one is a grit blade and the other has teeth - remove the one that has the teeth and just use the grit one.

When a grout says it's water resistant - it means that it won't fall to pieces when it gets wet and not that it will repel water, a popular misconception.

Just another thought, in the corners, did you use grout or silicone to run up the vertical corner joint between the walls? You really need to use silicone in these joints.

Good luck and keep us informed.

Thanks gcol.
It is hard to say exactly how much water escapes, perhaps an eggcup full after two showers. It doesn't flood out but wets surrounding timber, including the chipboard flooring (see later). In the main it emerges at the wall/tray/frame intersection (hard to be sure if that's all) and so either the grout or wall/tray seal must be reponsible. Tomorrow I will clean well with meths and apply more sealant in case this is the problem after all - it's just that this didn't help last time I had a similar problem. I must say I agree with one of the comments in the thread you included - use waterproof wallboard. I did this in one shower using Respatex and it's been great. I've done about 9 bathrooms in my time, without problems except once before, as I mentioned. By the way, the vertical joint is silicone sealed.
The tray is stonecast (760 x 760). Because the original shower had leaked in her flat I removed the chipboard and polystyrene floor and built up again from the concrete subfloor using 4 x 2 (on it's side) around the edges with 2 peices to support the middle, topped with 12mm WBP ply to bring it back to the original level. I then did the same again, (this time with the 4 x 2 on edge) to make room for the waste. everything was screwed and glued (with water-resistant grip fill) and the tray secured with grip fill too (rather than mortar). The tray was sealed to the ply walls with silicone (the sides angle in a bit) then I tiled down to the tray and sealed the tile/tray border when the enclosure had been fitted.
I think I have one of those grout removing tools, if I can find it. Otherwise I'll get on to Screwfit - thanks. Hope I don't have to use it after all.

I think you were right - wall movement! Not at the tray, which is very solid, but a few tiny cracks in the grouting. I did notice that the studs were on 600mm centres, not 400mm, and were a bit smaller than the usual 4 x 2 (3.5 x 1.8 ish).
It is hard to estimate the amount of water leaking because of how much may be absorbed but it is probably a few teaspoonfulls. The grout crack seems to affect mainly one horizontal joint (so far!) so I cheated and put some silicone on that for now. I will have to consider starting again but this will require moving my daughter and her flatmate out while I do the whole bathroom (I was trying to work around them with only the shower out of action before).
I could try introducing extra studs and noggins but it's difficult to match the depth of the existing. And/or I could try 18mm ply. Or even go for the Respotex solution this time. Any thoughts?
Nick
P.S. I did wonder whether I might be able to stiffen the wall by attacking it from the other side (i.e. from the hallway). Maybe extra studs glued to the existing ply and screwed to the existing studs. Not sure this would work.

Are we talking about a joint in the ply that's making the grout crack or just a grout line that's cracked? Is the crack in the grout over a join in the ply?
As you say, it might be easiest to try and brace the studs from the other side. 12mm ply should be fine but 600mm is quite a lot to have floating about. Still surprised you've got it cracking though.

The cracking is around mid height and affects both walls at the same level across most of the columns with a short vertical crack at the one end, before it reaches the frame. I don't understand this either as all the plywood joins are vertical - one wall is a single piece, the other has a vertical join where I fitted it around the existing mixer control (lazy sod).
If you come up with any ideas to save me bashing it all out that would be fantastic.

I meant to say it's just the grout that's cracked.
Nick

this could well be (it has been in my past experience) lack of sealant under the shower enclosure...where the enclosure bottom corner meets the tile and the tray. (not where u can see now but behind the enclosure)if there was no sealant there when u installed it then what happens water runs down the enclosure/tile joint ...gets behind the enclosure ..runs to the tray and out the back......
hope that was clear and poss helpfull in the future !!!

I sealed the tray to the wall before fitting the enclosure, then sealed the OUTSIDE of the enclosure. Perhaps I should consider sealing the INSIDE too in case you are right - I guess if any water found its way behind the frame it would escape by the same path you suggest. This does not seem to be the recommended practice in the enclosure-maker's fitting instructions but is there a problem with it in practice?

i'm not sggesting silicone down the length of the enclosure...just in that unseen bit, u could silicone the inside but this stopes it from airing well if it did get wet

might be worth a try thou

for a proper job you should of tanked the ply joints ...but easy to say now ..lol
an the joint between the ply an tray should of been rubber shower trim it NEVER leaks an no worries with a silicone seal......


enclosure-maker's fitting instructions ...if you have fitted it right you cannot go far wrong unless the tiles an tray are not right ..lol

tub mix should NEVER BE USED .....ITS AWFUL

OK, extra silicone hasn't helped at all. There are hairline cracks in several tile joints so presumably the wall is moving. In a month or two I will start the rest of the bathroom refurbishment. I will have to decide whether to rip out the shower and start again (I'd rather not) or see if anything can be done.
What if I re-grout using "flexible grout" or a grout additive? If I try this what about using a Dremel grout removing tool (I've seen mixed reviews) or a grout saw (hard work)?

To re-grout using a flexible grout is going to require you to get most of the grout out - if you were using the same grout then you wouldn't have to go so deep.
I have a Dremel grout remover bit - it does work, but you'll struggle if the tiles aren't spaced perfectly.
I think I'd have a go with the flexible grout and see what happens - it's not a great expense to try it.
I'd also be looking at beefing up the support under the tray. I'd hazard a guess that that's where your movement is coming from.