Shower advice - reference

[Another John]

I'm the one who asked if you should silicone the inside bottom edge of a shower cubicle, then went ahead and did it before everyone replied that you should NOT.

This apparently illogical advice ("siliconing the bottom edge will cause leaks, not prevent them") appears all over the net (why didn't I google in the first place ffs?).

ANYWAY: I found this excellent-looking site, which appears to tell you all you will ever want to know about showers and their installation:

[Grimly Curmudgeon]

It fails to mention one very good device, though. There's a sealing strip which can go on the wall, lapping over the tray and under the tiles before they go on. A bead of non-acetic silicone is pumped under the overlap and that type of seal lasts for years and years. One of the best type around and the silicone isn't cheap, but it works.

[Simon Stroud]

Hmmm... I've just been dealing with a related problem with one of my showers.

It's a Matki tray with a built-in "tiling upstand" round the back edge. It's been in for about 10 years without any trouble except hairline cracks have appeared across all of the bottom row of tiles.

When I installed it I followed the instructions to the letter. The built-in "tiling upstand" is recessed into the wall, i.e. tucked in under the bottom edge of the Aquapanel walls. All tiles except the bottom row are fixed using tile adhesive in the normal way.

For the bottom row I followed the instructions carefully. The tray itself has a load of silicone sealant behind the edge, between the tray and the wall. This oozes over the top of the tiling upstand all round. So far, so good. For the bottom row of tiles, I put a big bead of silicone over the front edge of the tiling upstand, and tile adhesive down to nearly the bottom of the aquapanel. The tiles were then squidged into this so they are mostly adhesive fixed, but their bottom inch or so is stuck (and sealed) with silicone. Then in one swift action I finished them off with a bead of silicone between the tiles and shower tray and neatly finished this. When all dry they were grouted in the normal way.

This was fine for about 8 years but then horizontal cracks appeared across all the bottom row of tiles. I assumed (correctly as it turned out) that with all the silicone behind, there was no real chance of water creeping through and soaking everything behind, but last weekend I finally plucked up courage to find my old stock of spare tiles and have a go at replacing the bottom row.

Getting them off was a right old faff. I used the angle grinder to cut a few slots so that I could break out sections without damaging the next row up. It turned out that the horizontal cracks were all in the area between the silicone and tiling adhesive - I guess the two materials move slightly differently so the tiles are stressed just there.

So now I need to work out the best way of re-sticking and re-sealing the new bottom row of tiles. Maybe there is a better (less flexible?) type of silicone for sticking and sealing the tiles to the tray?

Any advice?

Regards, Simon.

[Chris J Dixon]

I may be missing your point, but you seem to be reporting that movement between the tray and the wall has cracked the tiles. Wouldn't you need _more_ flexibility in the silicone to reduce the stress?

Chris

[Simon Stroud]

Hmmm... yep you could well be right. It probably is caused by the shower tray moving slightly very relative to the wall so super flexible silicone would be better. In the world of silicone, does super-flexible mean "low modulus" or "high modulus"?

Regards, Simon