plywood

[paulsa67]

how thick should I use ???...Its just normal floorboards which are ok i would say..

[GirlRacerRed]

the thicker the better. are you overboarding the existing floorboards or taking the existing up and replacing with just ply?

[paulsa67]

The existing floorboards will be staying down.

[GirlRacerRed]

the thicker the better then. 15mm at least if you're overboarding existing floorboards. 22mm thick if you can afford the height.

[grumpygrouter]

If the floor is solid, i.e. no bounce then you might want to consider using a cement based backer board. If there is bounce it needs dealing with first. This is where you can either ply over the top or strip back to the joists, reinforce and noggin them and then overboard with 18mm ply and 6mm backerboard on the top.

[paulsa67]

I was told 9mm would be ok...

[GirlRacerRed]

I was told 9mm would be ok...

who advised you that 9mm would be ok?

[grumpygrouter]

I was told 9mm would be ok...

9mm ply will add very little strength to your floor, and could be susceptible movement from the moisture in the adhesive. 9mm is def. not advisable.

[paulsa67]

who advised you that 9mm would be ok?

i tiler i spoke to.

[grumpygrouter]

i tiler i spoke to.

Hang around on here for a while and see how many of the long established tilers on here agree with your advisor. Not too many I suspect.

[deanotile]

9mm is not suitable it will have to be a minimum of 15mm but we only do 18mm so as above if the floor has no bounce go with a tile backer board this can be as little as 6mm thickness.