hi guys, i have a tricky bathroom floor to tile soon and could do with some advice. the floor is approx 6msq, ceramic tiles ( 333x333). the existing floor is half chipboard and the other half is the old fashioned plank type floorboards.the customer wants the floor raised to the miniumum possible. i was thinking of making sure existing floor is secure and then boarding out with 6mm marmox board and then go for bal spf or ardex 7001 then finish off with a flexible grout. would this be ok and would any primer be required? any advice will be a great help.

If the customer wants a minimum raise in the floor then you could strip off the chip board and floor boards and replace with sheets of 18mm Ply (screw down to joists every 30cm). Personally I'd use a thin backer board over that but you could get away with a flexible addy directly on top of the ply.
Ply will need sealing including the edges.

yeah i mentioned that and she dont want the aggravation or the extra cost !!!

What is the floor like in general, is there any give in the joists ? I would go minimum of 12mm wpb on top of existing floor after it was made secure, then flexi addy and grout.

Only 'if' the joist had no movement, trouble with trying to cut corners to suit customers 'wants' is that can come back and bite you in the backside, especially when grout and or tiles start cracking, you have mentioned this I assume ?

sure have! i was just trying to see if any of you guys had an alternative answer. if i do rip the floor up and re-lay with 18mm wbp ply would you tile straight on top of this or put down some 6mm ply or backerboards 1st?

Originally Posted by negsy26

sure have! i was just trying to see if any of you guys had an alternative answer. if i do rip the floor up and re-lay with 18mm wbp ply would you tile straight on top of this or put down some 6mm ply or backerboards 1st?

Absolutely no way! you would be introducing another fexible layer to tile onto. If you must, lay 6mm hardieabacker, glued and screwed and tile with Mapei Keraquick, or even latex plus additive if you want to be really sure.

If you dispense with the hardie and go straight down onto the 18mm ply then Ardexflex 7001 is excellent but you must prime the tiling face first with P51 primer. Oh and the underside and edges should be sealed with Polyurethane varnish prior to laying.