Marble / travertine.

[tonym]

Thanks for all the replies. So its 12mm hardie backer to prepare the wall for 12mm marble tiles. If the marble tiles were used for the floor what would be the best floor substructure. It is a new loft conversion so at the moment it is only 8"x2" timbers. The floor area is about 8x8 ft. Would 12mm hardie backer be ok or should it be 18mm marine ply?

 

[Rich]

Id always go with a backer board over ply given the choice.

 

[tonym]

So 12mm backer board instead of ply on the floor? Just out of interest can I ask why?? Would it be better adhesion for the backer board or greater stiffness ?

 

[Rich]

Of course you can.
Backer boards will not rot with moisture, if and moisture gets to the ply wood (through the grouting, Silicon or from underneith) it will swell and rot, this can stain the grout or even pop the tiles off. And you will get a better bond to a backer, I use 2-part on any wood, although most tilers will use a single part, to make sure but will happily use a single part on a backer board.

 

[tonym]

Do you think a double layer o0f 12mm backer board cross fixed with staggared joints would be overkill and is ther any difference in quality with the baker boards, or could you reccomend a backer board brand?

 

[Rich]

I use No More Ply but plenty of the guys on here use Hardie, to be honest I think they are pretty much the same thing, you can get thicker board if you need it, NMP goes up to 50mm. Why do you want to go so thick? Is there a lot of movement in the floor? What is on the floor at the moment?

 

[tonym]

Previously i had a porcelain floor put down. The floorboards were taken up (circa 1920's house) and was recommended 25 mm ply straight onto joists. This place is around the corner. Its my sisters house and considering the weight of the tile iI want to make it belt and braces, as I don't want her complaining a few years later.
There shouldn't be any movement in the floor considering its a new floor of a new loft conversion. There is nothing on the floor at the moment. It is just exposed 8x2" joists.

 

[Rich]

You could always lay ply then over lay with a backer board like NMP/Hardie, just make sure the floor is as solid as poss, adding extra noggins if needed and seal the underside and the sides of the Ply before laying.

 

[tonym]

thanks. Thats a good idea. Would the Bal Primer be good enough as a sealer for the Ply??

 

[Rich]

I couldnt tell you to be honest, as I said Im a Mapei man so Im not familiar with BAL products but you dont have to prime the NMP, you can dampen the boards with a sponge or rag before spreading your adhesive instead.