Bathroom floor - plywood or hardibacker?

[ecmm1973]

Hi.
Had some great advice last time I used the forum about tiling walls.
Now I've decided to tile my bathroom floor and there's a few things I'm not sure of.
Hoping someone can point me in the right direction....(don't have the confidence to just go ahead and do it without checking with experts!)

The bathroom floor is old pine floor boards (1930s house). I want to overlay either plywood or hardibacker board.
I don't have the guts to try and remove the bath to rip up the old floor boards so will have to overlay.
I'm not sure which one to go with - plywood or hardibacker board. I want to put down Homelux floor matting to try and have some waterproofing and also to account for floor movement so the tiles won't crack.

Am I right to think that if i overlay with plywood then it should be 18mm plywood just like this:
Exterior Plywood 18x1220x2440mm - Plywood - Sheet Materials -Building Materials - Wickes

or should I use structural plywood?

Would I then just screw the plywood down into the floor boards (and hopefully some joists too) or would I need to put some sort of adhesive between the floor boards and the plywood?

I've read that 6mm hardibacker board can be used on floors (this would mean less of a threshold from the landing into the bathroom) but it must be laid in a bed of flexible adhesive. Does this mean I would just need to put tiling adhesive directly ontop of the floor boards, put the hardibacker board down in to the adhesive and screw through to the floor boards? Would I need to prime the old dirty pine floor boards first?

I'm probably going to run some floor tile around the room as skirting. Should I run the Homelux floor matting up the wall a little too?

Sorry to have so many questions. I'd be really grateful for any advice.

Many thanks,
Eric.

 

[DHTiling]

Hi Eric, how sturdy are the floor boards.?.. any bounce/movement and are they in good condition.?

 

[Bubblecraft]

Hi Eric. Your best bet would be hardibacker. 6mm will be fine as long as it is relatively level. Make sure your floor boards are as secure & deflection free as possible. Boards can be put down with a single part flexible adhesive & then screwed. The adhesive should take the inferfections out your boards. I personally like to put an SBR primer first to make floor boards less porous & secure down any loose dust particles.
Ply of course can be used but can work out rather costly and time consuming. 18mm WBP ply or Marine would be advised. All edges & underside will need to be primed with an SBR. DO NOT coat the surface. Structural ply CANNOT be used such as oriented strand board (osb) or sheathing ply (Elliotis). This would need to be screwed only no greater than 150mm centres.
Do you have a tanking for your shower area also as you mentioned that you were coating the floor only but wish to continue up the wall?

 

[ecmm1973]

Hi Eric, how sturdy are the floor boards.?.. any bounce/movement and are they in good condition.?

Hi David,

Thanks for replying. The floorboards aren't great - they've been cut up by a plumber in the past. There are some gaps and there is some uneveness in that one board might be a few millimetres higher or lower than the next one. There is some bounce but no more than in the rest of the house. I'm in the process of trying to rip up the old thin (4mm) ply that was already there (and was glued down with some sort of no nails stuff) - having a nightmare getting it all up - don't think I'm going to get it all off - so I don't think I'm going to get the floor boards perfectly flat.

Thanks,
Eric.

 

[ecmm1973]

Hi Bubblecraft,

Thanks for your help. There is a difference of a few millimetres between different floor boards.
So, you'd say that putting don plywood is more time consuming than hardibacker board?
Is it OK to put down 12mm hardibacker board (you said 6mm is fine as long as it is relatively level but I'm not sure what you/tilers/experienced people would regard as relatively level) on a floor or is it too heavy?

Shower - Homelux wall matting down. Bathroom isn't fully tiled - just the shower area and above the bath

My concern with using Hardibacker board is that I have to use the adhesive to "stick" them down (and screw) meaning that if I mess it up and the backer boards move/are uneven/messed up I'll have a nightmare trying to get all the adhesive up again so I can start again. How straightforward is it?

Thanks for all your help.

 

[charlie1]

Do hardie technical not recomend you fit there boards directly on to plywood?? Im sure they do, so its not an alternative to ply, its additional (strictly speaking)

 

[beanz]

Get the floor boards as bounce free as possible. You may need to put extra noggins in, where the plumbers have been hacking it about. If some of the floor boards are too bowed, and are sticking up too much, you could cut them out and replace them with new. If the floor feels pretty good after that, i'd usually use 12mm exterior ply, but 18mm can only be better, so if you don't mind the step.. Use that.

I've never used Hardibacker on floors, so can't really comment on that.

 

[Rookery]

Screw the existing t & g boards to the joists, replacing any dodgy pieces. Clean floor boards & prime with SBR.
Fix 6mm Hardie with flexi adhesive & screws. Wipe back of boards with damp sponge 1st to remove the dust.
Tile.
I wouldnt bother with the Homelux matting on the floor. It wont stop movement/cracking and you're not creating a wetroom so its pointless. If you're concerned about lateral movement use an uncoupling membrane such as Dural or Ditra.
Tank the shower area walls with a paint on shower tanking kit such as Mapeis or BAL's.

 

[Diggy]

12mm ext ply minimum for me on floorboards everytime , then Elastomeric to fix.

DbD

 

[cam_low]

Screw down and bouncy boards, Prime, glue and screw 6mm hardie, tile your floor. Plys a waste of time these days when such products like hardie are out in the market.