Preparation for marble tiles?

[Veglen]

Hi guys n dolls,

Just hoping somebody could offer me some advice pls?

I am looking at purchasing some marble tiles. The size is 305mm x 610mm x 12mm. They are bevel edged and very heavy.

The tiles will be going in a bathroom and I have already removed the old tiles from the walls. However, the plaster has come away with the tiles in some areas and some of the plaster that is left on the walls is loose.

My question is, do I remove all the plaster from all 4 walls and dry line, or do I remove only the loose plaster and have the walls patched up and re-plastered.

As I said, the tiles are very heavy weighing 6kg each, and I have 24sqm of wall area.

Any advice on how to prepare the walls ready for the tiles would be greatly appreciated.

Thanks in advance
V

 

[1john]

Plaster wont be strong enough to hold those tiles. Is you wall rendered behind the old loose plaster?

 

[Richard C]

As 1john said, plaster won’t take that weight. I make it 32.25 kg/sqm for the tiles, add on 4 kg/sqm for addy/grout = 36.25 kg/sqm.

Some figures;
Plaster in good condition - 20 kg/sqm
Unplastered plaster board - 32 kg/sqm
Render in good condition & lightweight tile backer boards - 40 kg/sqm
Heavy duty tile backer boards – around 60 kg/sqm

So fixing over a new render base would be an option BUT if you re-render, you will have to wait 4 weeks before you can tile it unless you use a specialist quickset render (expensive). Another option is to repair the holes in the render you have with powder tile adhesive but this will only work if the existing render is in a suitably good condition to accept the weight of your tiles &, again, if the repairs needed are extensive then it’s expensive & cheaper to use a quickset render.

There is a possibility you may be able to tile directly onto the brick/block wall after stripping back but I wouldn’t advise it & it’s cutting corners really. It also depends on what the wall is made of & most important of all how flat it is. With tiles that size you need a really flat tile base or they will be all over the place & it will look terible.

If time is a problem, the best option would be to strip it all back, fix a suitable waterproof tile backer board & tile straight onto that.

Another factor is if you intend to fully tile or are some walls to be ½ tile with plaster finish?

 

[1john]

Richard, slight hi-jack but do you know if tanking affects the holding weight as it is essentially a new skin?

 

[Richard C]

Richard, slight hi-jack but do you know if tanking affects the holding weight as it is essentially a new skin?

A liquid membrane such as WP1 or the Dunlop equivalent has a max 32kg/sqm. Physicaly bonded membranes will be equal to but no better than the substrate you’re bonding them to; but always check the spec sheet

 

[Richard C]

A liquid membrane such as WP1 or the Dunlop equivalent has a max 32kg/sqm.

What I should have made clearer is that it won’t, of course, increase the strength of a weaker substrate such as plaster.

 

[Veglen]

Thanks for taking the time to reply guys

1john, in answer to your question

Plaster wont be strong enough to hold those tiles. Is you wall rendered behind the old loose plaster?

No only one wall appears to be rendeded. Two of the walls are external and brick and two walls are internal and single skin hollow block brick if that makes sense!

Thanks for the info Richard C, very informative

Another factor is if you intend to fully tile or are some walls to be ½ tile with plaster finish?

I intend to fully tile.

I’ve now taken the plaster completely off of three of the walls. One of the external walls above the bath appears to have been rendered but only to the top of the bath, below is just brick. I've left this on for the moment.

If baker boards are the way to go can you offer any advice on how they should be fixed to the brick and will I need to render the walls first.
Also what thickness of board would you suggest?

Any more help on this subject would be great
Thanks in advance
V

 

[Richard C]

Use only 12mm (or similar) waterproof boards for walls & do not render before fixing. Method of fixing varies depending on circumstances & which make board you choose but fixing direct to brick will typically involve either battening & fixing to those or dot & dab adhesive direct onto the brickwork with the additional of mechanical (through) fixings which is essential in order that the boards are securely fixed.

 

[Veglen]

Thanks for the advice Richard C.

I’ve arranged for a plasterer to come and put the Backer Boards up. He suggested adhesive dabs at 300mm centres and a screw into the brick through each dab. He was a little worried about the hollow block brick but thinks the adhesive should help them hold the screws better.

It does sound all a bit OTT to me. But if I hadn’t have asked for advice here I would have just had the walls dry lined in the normal way using plasterboard and probably have them fall down under the wieght at a later date.

It's a shame the tile shops doen't explain that these types of tiles won't just go on any wall when you buy them.

Only one tiler out of three that have quoted to tile the bathroom mentioned the weight and requested a strong surface to tile onto too!

Thankfully, I asked for advice on here and received some very helpful information.

Thanks again for the advice.

See you next time I have a problem.
Kind Regards
V

 

[tictic]

is there not any room for battens..

stagger the boards onto the wall and use fiba tape with flex ashesive for all board joins and internal corners etc...

when grouting marble you will want an unsanded grout,so you dont scratch the tiles..

dont forget a good sealer for them to.