Help needed for Slate tiling

[Vernon]

Hi,
I'm renovating our bathroom and would like some advice please on the following points. At present the walls are bare brick which I can either re-plaster with a cement based plaster or cover with 12.5mm impregnated plaster boards mounted on a metal framework. The floor will be new laid concrete. The shower will be a walk in style, so I'm intending to tank the wet area plus an extra 50cm all round. I’m intending to use a membrane tanking system as opposed to paint on sealant.


For the walls I’ve got two sizes of slate tiles 60cm x 60cm x 14mm thick and 60cm x 30cm x 12mm thick with an approximate weight of 30kg m².


Which backing would be the better one to use?


What is the required adhesive bed thickness and trowel rib size?


And when the tiles are pushed home, what is the approximate thickness of the adhesive left that they are bedded into?


On the floor I’m using 40cm x 60cm x 12mm slate tiles. Again what’s the bed thickness needed?
The floor will have under floor heating from an end loop off the wall radiator.


On both walls and floor I'd like to have just a 1mm grout between the tiles. Does anyone see any problems with using so small a grout?


Thanks for your help.
Vernon.

[beanz]

A 1mm grout line with slate sounds like a bad idea to me!?! The nature of slate is that it varies in thickness, so reallistically you want a 10mm gap, so you get a more gradual change in height. With a 1mm gap i think you'll end up tripping on the edges/corners of the tiles.

Those tiles exceed the weight limit for plaster skim, and will probably exceed for plasterboard too, by the time you've added your addy n grout etc. Safer to go with some sort of tile backer board IMO.

I'm not 100% sure on trowel size for this, to be honest, so i watch with interest...

[medlar]

if it were me i would fix a cement based backer board to your walls,and use a 10mm serator,the weight far exceeds the limit for skim coat or plasterboard. i would go for a 6mm gap.

Jimmy

Chinese slate floor

[beanz]

I like that chinese slate Jimmy, never seen that before.. Looks good!

[grumpygrouter]

if it were me i would fix a cement based backer board to your walls,and use a 10mm serator,the weight far exceeds the limit for skim coat or plasterboard. i would go for a 6mm gap.

Jimmy

Chinese slate floor

What's with the blue paint Jimmy?

[pjc]

The best surface would be render and i presume your slate is honed if not you have a sense of humor ? if you are wanting to put a small grout joint 2mm would be a little better but that is still smaller than recommended :Pete

[faithhealer]

Agree with render on the walls and don't even think about small grout lines on slate. Always been told 5-8mm. One bloke I met used his little finger as his 'guide'!

[pjc]

Agree with render on the walls and don't even think about small grout lines on slate. Always been told 5-8mm. One bloke I met used his little finger as his 'guide'!

if its honed i have laid it with 2mm joints quite often we have to lay all stone with a 2mm joint but my guess is its riven then its fingers and toes lol

[Vernon]

Thanks for the info guys, Beanz and Medlar mentioned the backer boards. I read about these on this site before. However, my problem is that I'm in Austria and as of yet I can't find a supplier over here who has tile backer boards.
If there's any Austrian tilers on line I'd be grateful for advice on this one! I've bought my slate from a supplier who reckons that 1mm grouts are possible, but he's no tiler!
PJC what's riven in tiling?
The slate is graded to the set thickness and square cut on the edge. Is honing taking the corners off?
Vernon.

[grumpygrouter]

Riven is the natural, non smooth finish of the tile Vernon. If the slate is honed it has a smooth surface (not riven). Also if it has been accurately machine finished, a tight grout line may be possible but I certainly would not like to be trying to get a consistant 1mm joint unless your surfaces are absolutely flat and your tiles are very very accurately machined.

[Vernon]

Thanks Grumpy, I'm a DIYer not a pro like yourself so I don't always understand the terms. The tiles are honed to a smooth finish, but are not totally flat, there's still a slight bit of undulation to the surface. I was going to use a slate with a riven surface and I would have had to have flaked them off and graded them thickest to thinnest before laying them, but the supplier is more or less guaranteeing a standard thickness to the tiles. However, I'm still intending to grade them before fixing.

[doug boardley]

deffo go for a bigger joint Vernon, reading tat your tiles are honed but with undulations I'd recommend nothing less than 4mm
Good Luck
Doug

[Vernon]

Thanks Doug, I'm still out on this one, but it looks like my dream of small grouts is going out of the window. I had not been able to find any 1mm spacers over here anyway, so was going to have to get them from the UK.

[beanz]

Will a cement based plaster render take i heavier load then? I wasn't aware of a distinction if i'm honest!?!

[doug boardley]

Will a cement based plaster render take i heavier load then? I wasn't aware of a distinction if i'm honest!?!

you can have a gypsum based plaster Beanz ie browning, bonding,renovating,one coat etc. Cement based is sand and cement

[whitebeam]

Yes it will due to the strength of the render, worked on many refurbs and render has always been used for the tilers

[doug boardley]

yep, sorry, forgot to mention that the gypsum based plasters are no good to tile on! to busy explaining that there were other renders opposed to s/c

[Vernon]

So Guys,
It sounds like my option of using cement based plaster instead of plasterboard is the best choice if I can't find backer boards over here. But, the weight limit m² still seems to be a problem. What does IMO stand for anyway? Knowing this should help my search.
Cheers Vernon.

[whitebeam]

Sand and cement is still cheaper than some the ready mixed versions

[doug boardley]

So Guys,
It sounds like my option of using cement based plaster instead of plasterboard is the best choice if I can't find backer boards over here. But, the weight limit m² still seems to be a problem. What does IMO stand for anyway? Knowing this should help my search.
Cheers Vernon.

in my opinion Vernon, look on it as a type of disclaimer!

[Vernon]

That's true Whitebeam, but ready mix is the easiest option for me to buy here. I just hope I can locate backer boards.

[beanz]

you can have a gypsum based plaster Beanz ie browning, bonding,renovating,one coat etc. Cement based is sand and cement

Cheers Doug. I know about Gypsum based plaster; i was just confused by cement based plaster, and the weight limits!?!

[foxman]

Quality job mate!

[R Montgomery]

I would go with a bonderiser on the brick then a sand,cement and lime mortar bed.Then a paint on fibreglass reinforced membrane.A 5mm trowel should do it just put a flat skim on the back of the tile as well as the notched coat on the wall and check for 100% coverage.I would use a wider joint size but if the tile is smooth and they are the same size and square 2mm might look good.Lay some out dry on the floor to get an idea of the different looks.Good luck!

[Vernon]

Thanks R Montgomery!
I've not given up just yet on my search for backing boards. However, I think I'll probaly be going ahead with the render and I'll see waht type of membrane I can track down. I know I can buy Mapei or Schluter products over here so I should be able to come up with something of a reasonable quality. And I'm still going to try for the 2mm grouts.
Vernon.

[R Montgomery]

Laticrete also make some great stuff like Hydroban but for an area that is prone to movement like a new concrete slab and its links with other surfaces I would use the 9235 but everything needs to be smooth and patched up.Good luck with the 2mm.Hope you have plenty of wedges.

[Vernon]

Thanks again for the info. I've just viewed a you tube video on laticrete and it easy to use.

[LM Ceramics]

deffo go for a bigger joint Vernon, reading tat your tiles are honed but with undulations I'd recommend nothing less than 4mm
Good Luck
Doug

i agree wouldnt like to risk it for a 1 mm joint you could hit into problems