Please help i have new 18mm tongue & groove chipboard floring in my bath room fixed and screwed @ 150mm spacers totally solid & am going to lay wbp ply over the top so i can tile on this i am going to seal this with a mix of sbr bond & cement slurry then tile with floor tiles my questions are what thickness ply do i need (i dont want to raise floor to high was thinking of 6mm too expensive to pull up tongue & groove chipboard now ?) & am i sealing it correctly & what adhesive do i use & is the grout & adhesive better if i get it in powdered cement base form or ready mixed i have been told so many different things please help many thanks

BS states 15mm ply minimum for tiles floors, 6mm is too thin. but don't ply the floor anyway as there are better substrates to tile too, use tile backer boards instead. I would recommend 6mm 'No More Ply' (google it)

Do not use ready mixed tile adhesive on the floor despite what B&Q and Unibond tell you.

Instead use a flexible cement based adhesive, if you must shop in B&Q then get an adhesive called 'Buildfix' it is the B&Q name for a Mapei adhesives. In addition use a flexible grout, something like Mapei Ultracolour Plus

Yes seal it with an SBR or a dedicated tiler primer, do not use PVA. You do not need to use a slurry mix

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Professional Kitchen & Bathroom Fitters | Master Painters and Decorators | Brighton & Hove

excellent thanks but few more questions sorry
1st how do i fix the backer boards down
2nd do i seal straight over them & do i use sbr bond
3rd adhesive best to buy from tile shop somewhere like topps tiles for example
your help is greatly appreciated

OK...

There are many different types of tile backer boards on the market, some require primer others don't

'No More ply' as i've listed does need a primer in most cases and yes an SBR is fine BUT you may want to consider a primer recommened by the adhesive manufacturer. So if you were to use Mapei Adhesive then 'Mapei Primer G' or say you use BAL adhesive then BAL APD.... and so on

As I say other backer boards don't require a primer so follow the advice on which ever brand you use to validate any guarantees

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Professional Kitchen & Bathroom Fitters | Master Painters and Decorators | Brighton & Hove

ok you edited your reply

1) With 'No More Ply' it is glued and screwed down, they make there own glue to fix the boards with so use this
2) answer above
3) No don't use Topps as they will rob you blind as you are not trade, they are plenty of other suppliers out there, try either a local tile merchant or tile giant or CTD or HTW... anywhere but Topps!

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Professional Kitchen & Bathroom Fitters | Master Painters and Decorators | Brighton & Hove

thanks very much you are a lifesaver

Although the advice is always that you should not tile onto T&G chipboard flooring, I am yet to venture into a property which has problems where it has been done. I venture into hundreds each year on 15 year old (plus) developments.

If you wish to overlay then Ditra mat will be a good option for you which will keep the finished floor level minimally higher than it is now. Plastic ply (supplied by Nichols and Clark) is another good product.

Although I have heard some tradesmen have had problems with plastic ply, I have never seen anything on the web to indicate as such or had feedback from tilers I know which gives a negative impression.

Marmox do a 4mm backer board. Its what i'll be using on top of my 18mm ply in the bathroom. I'll be laying it with Mapei flex tile adhesive

Use a good grade far eastern ply and you won't need the marmox. Travis Perkins are dear but top quality ply, although when compared to cheap ply it isn't that expensive at all because it will not start to fail.