Preparing old bathroom walls for large format tiles

[meanpeach]

I'm renovating an old Victorian property, as part of this I am refitting a new bathroom which will have wet room type shower in one corner and large format tiles on the walls approx 30x40cm. The present walls are finished with the original wet type plaster about 3/4 inch think, while not the flattest surface I've seen, they do seem to be adhering to the brick work pretty well.

What would be the best way to create a good base for these tiles, especially around the shower area. As far as I can see my options would be to skim the present walls then seal them with a tanking product - but would this give me a sufficently flat surface and be resiliant enough for the shower area.

Or should I go back to the brick, baton the walls and put up new aqua board. If I do this, do I still need to get the walls skimmed or can I get a tiler to put the tiles directly onto the aqua board??

I had previously posted this on the building thread, but the only advice I got was to "Overboard the walls with 12.5 mm WBP. Probably plug and screw if the walls are good. Seal the board with dilute pva, 4 to 1 ish, this will prevent any bleed through to the grout from the board. Then tile. Take care to eliminate any movement between adjoining boards in the corner". But I wasn't convinced.

Any info or advice would be greatly appreciated.

 

[gcol]

As far as I can see my options would be to skim the present walls then seal them with a tanking product - but would this give me a sufficently flat surface and be resiliant enough for the shower area.

If you get it skimmed properly it'll be fine. Tell the plasterer you intend to fit large tiles so you need it to be dead flat.

Or should I go back to the brick, baton the walls and put up new aqua board. If I do this, do I still need to get the walls skimmed or can I get a tiler to put the tiles directly onto the aqua board??

You can do this and it would give you a better surface to tile onto. However it's more work and cost. Fitting instructions for aquapanel here http://www.knaufdrywall.co.uk/files...esKnauf_DrywallLiteratureAquapanel_Mar_06.pdf

I had previously posted this on the building thread, but the only advice I got was to "Overboard the walls with 12.5 mm WBP. Probably plug and screw if the walls are good. Seal the board with dilute pva, 4 to 1 ish, this will prevent any bleed through to the grout from the board. Then tile. Take care to eliminate any movement between adjoining boards in the corner". But I wasn't convinced.

Ply isn't the best thing to use around a shower and PVA is a no no where water is concerned.

 

[meanpeach]

Great thanks for that, and the link. I kind of figured the WPB/ PVA suggestion was probably not a good one

As a matter on interest. I'm replacing the floor, which is presently old floorboards on joists (mixture of rotten and split) with WPB. I am tiling the floor and want to include underfloor heating, going the devimat route. But I'm considering using the underfloor heating as the sole source of heating (150W).

I've been told that I can do this if is I use a thermal board over the WPB. If I went this route, could I use 18mm WPB as my base, (then thermal board, then the devimat, then the tiles). Obviously concerned of the height of this sandwich.

Or if I decided to go with a lower wattage underfloor heating, i.e. not using the thermal board. What thickness of WPB would be best?

Thanks in advance for any advice.

 

[gcol]

As a matter on interest. I'm replacing the floor, which is presently old floorboards on joists (mixture of rotten and split) with WPB. I am tiling the floor and want to include underfloor heating, going the devimat route. But I'm considering using the underfloor heating as the sole source of heating (150W).

First off, I cannot recommend the use of 18mm WBP as a base, I would use 25mm to be 100% sure of a sound job. Secondly, devimat specify 100W/m2 as a maximum for wooden floors. Thirdly, I hate underfloor heating, I think it gives off very little heat for what it costs and I certainly wouldn't rely on it to heat the room.

Or if I decided to go with a lower wattage underfloor heating, i.e. not using the thermal board. What thickness of WPB would be best?

100W/m2 and 25mm WBP.

 

[meanpeach]

Cheers for the info.

I suppose UFH is all about personal preference. But it was a company that supplied devimat who said you can use 150W on wood, if it's laid over thermal board?

I kind of figured 18mm would be too thin. Just wondered if I did go the thermal board route whether that would add any strength to it, thus giving me the option of using a thinner WPB.

 

[gcol]

http://www.devi.co.uk/downloads/devimat/08098002/
Top of page 2. You probably could use a higher rated heater with the thermal board, but I would rely on it for any structural help.