As the title really what adhesive should i be using to stick the hardie down onto chipboard, spf or ultimate flex? I'll be screwing the chipboard to the joists as its currently nailed, then screwing and addy for the hardie, heat mat and leveller then tile with spf and porcelain.

Assuming you mean Granfix Ultimateflex, then that will be fine for the hardie and the tiles.

So spf's a no-no then? I wouldn't use it to tile onto chipboard but is it also unsuitable to hold hardie down even if its screwed as well?
If it is it means hardie backer and ultimate flex works out a lot dearer than plying.

Keraquick will be fine for this...As you say it's the screws that hold it and the adhesive is to fill voids really...

Originally Posted by Dave

Keraquick will be fine for this...As you say it's the screws that hold it and the adhesive is to fill voids really...

None of the local shops stock Mapei is Keraquick a standard spf?

It is an S1 type but others will be fine to use underneath...maybe a good quality for the tiling bit though....ulimate flex is sticky stuff....

Originally Posted by Dave

It is an S1 type but others will be fine to use underneath...maybe a good quality for the tiling bit though....ulimate flex is sticky stuff....

It is indeed and it ain't cheap, but i dont want anything lifting so - screw chipboard down, spf and screw hardie, lay u/floor and level compound, tile with ult. flex not spf?

If you level with a fibre enhanced slc then you will be ok with normal rapid flex adhesive...

Mapei fibre plan is a good one and weber niv is another....both add strength to a solid timber floor..

I'm using tilemasters slc it's fibre reinforced so should be good to go cheers for the advice.
Lee.