Problem with tiled shelf under a shower - TilersForums.com

[leaking]

I'm having problems with a mosaic tiled ledge (12.5cm wide and 8cm up from the bath) in my bathroom. It is on the wall side of the bath and the taps come out of it.
I tiled onto 12mm exterior ply, no primer, over a wooden structure I built to support it. I used grandfix supergrip and granfix flexible limestone grout. I have just taken the tiles up because they were coming loose and there were cracks in the grout. Obviously I've done something wrong!
I think there must be some tiny movement in the shelf structure, but also the wet is getting right through to the ply where it is under the shower - its gone black! The tiles on the wall are fine.
This is my second attempt to fix this problem - I would really value some good advice. Thanks.
Tamara

 

[grumpygrouter]

You have made the mistake of thinking that grout is waterproof by the sounds of it. Firstly. ply is not a suitable substrate to tile onto in a wet area. It "moves" too much with differing atmospheric conditions. it is the expansion and contraction that has cracked your grout. Water has then got through it and penetrated the ply.


Your best solution, in my opinion, is to remove your current ply shelving and rebuild it with a tiling "backerboard" such as Hardiebacker 500. This is a cement based board that is unaffected by water. Re-tile with your chosen mosiacs and I would suggest an adhesive like BAL whitestar or Mosaicfix (better!) and BAL microflex grout.

PS welcome to the forums Tamara.

 

[leaking]

Wow - thanks Grumpy! Thats great - there are only so many times I want to take my bath out!

My mosaic tiles are semi tranclucent so the grout underneath effects the colour. The granfix adhesive has a greyish colour - would either of your recommended adhesives match?

Tamara

 

[grumpygrouter]

BAL mosaic fix is white and is actually designed to address this problem (white star is white also but not quite as "white" if you see what I mean).

What you need to do when fixing your tiles is to try and ensure you get a "solid bed" of adhesive on the back. This means that you have complete coverage with adhesive on the back so it eliminates colour variation. You may well be better doing this in 2 stages. Once you are ready to start tiling, it may be best to "skim" your shelf with a thin even layer of adhesive and let it dry. The adhesives mentioned will need to be left overnight as they are not rapid setting. Once it is dry, apply your adhesive with 3mm notched trowel, lay up you mosaic sheets (i am assuming they are sheets, right?) and pad them gently into place using a grout float or other flat surfaced tool. Try to keep you grout lines clean as you go along as these adhesives are really good - such that it makes cleaning off set adhesive very difficult!

When set - min 16hrs, grout with BAL Microflex grout and leave to dry. next day seal the edges with BAL Microseal silicone sealant. These 2 products contain a substance called Microban which deters fungal growth.

Good luck and maybe you could post us some pics to show how you got on?

 

[leaking]

The problem is that the walls are already fixed with the grey granfix colour, so if I do the shelf in white it will look odd. Thats why I was hoping to use a similar grey for the adhesive.

Unfortunately my tiles are no longer on backing sheets as I had to take them off the shelf to re-use since I already used my spares last time I retiled the shelf and they are no longer stocked! I'm still cleaning them up - only 320 more to go...

Also I previously just used grout on the front edge of the shelf. Can I get away with this or do I need to use plastic edging?

 

[grumpygrouter]

The problem is that the walls are already fixed with the grey granfix colour, so if I do the shelf in white it will look odd. Thats why I was hoping to use a similar grey for the adhesive.

Unfortunately my tiles are no longer on backing sheets as I had to take them off the shelf to re-use since I already used my spares last time I retiled the shelf and they are no longer stocked! I'm still cleaning them up - only 320 more to go...

Also I previously just used grout on the front edge of the shelf. Can I get away with this or do I need to use plastic edging?

In that case then, and this is really second best, you can use BAL Single Part Flexible adhesive instead. Has 5hrs life in the bucket so plenty of time to work with (same as mosaic fix). It is suitable for mosaics and wet areas but isn't quite as smooth as mosaic fix. Although the hardiebaker is grey, you may still want to give it a skim first but because the adhesive is grey you probably get away with it.

Plastic edge trim is there for two reasons, 1; to give a "nice" finish to the job and 2; to give a bit of protection to the edge of the tiles. it is up to you how you finish the job. Most important thing is to make sure you have a good coverage of grout in your lines and that your tiles are clean and grease free when you apply the sealant so it has the best chance to stick properly.

I am not familier with the characteristics of granfix products which is why I haven't mentioned them.

I have just noticed that you have used a limestone colour grout originally, BAL microflex doesn't come in Limestone, only white so you may well need to use the same grout again. Do you know how flexible it is?

 

[leaking]

I used granfix extra fine limestone grout mixed with granfix flexible additive 125ml to 1kg as instructed on the bottle. Granfix was the make recommended by the people I got my tiles from.

 

[grumpygrouter]

I used granfix extra fine limestone grout mixed with granfix flexible additive 125ml to 1kg as instructed on the bottle. Granfix was the make recommended by the people I got my tiles from.

Your grout almost certainly cracked then because of the damp getting to your ply. As you used a latex additive, normal movement should easilly be compensated for. This problem shouldn't re-occur if you used backerboard.