fixing floor for tiling - replace boards or entire floor

latecomer

We are going to be tiling our bathroom floor in the near future and the existing floor isn't in great shape and needs at least some boards replacing. I was going to pull them up and replace with new tongue and groove boards and overboard with ply for the tiles but I'm thinking this will leave a fairly large step going into the bathroom due to hallway being just sanded boards. Then I've thought about taking them all up and just putting down thick WPB ply instead which from searching does seem to be another solution. Has anyone done this? Does it need sealing before tiling etc?

Thanks in advance!

MX5huggy

Done exactly as you say 4 times now 18mm WPB screwed down at 200mm centres, with nogins between the joists so that all the edges are totally surpported. Then use a high quality flexible adhesive (BAL is best). Dont use any sealant and dont even think about PVA!

latecomer

I certainly wasn't going to PVA anything other than the walls where I'm patching up the plaster

Thanks for the reply. That sounds like the way forward as I'm fairly certain that the boards under the bath are pretty bad and I suspect the ones around the toilet will be equally bad. I need to get down under the floor at the weekend and check out the state of the beams so I can have a good look while I'm down.

Sobraon

I had a similar issue and in the end paid out for 24mm WBP - probably over engineered but a very solid job.

latecomer

I dont mind spending a little extra to get the right results but I'm concerned about the step up into the bathroom as there will be tiles going on top. If 18mm is sufficient then I'll probably go with that was it will keep things more level. Of course if we go for a carpet in the hall in the future then it would probably be too low.......cant win then all!

missile

Exposed tile edge does not look pretty. You might want to lay a coving strip. These fit under the tiles and make an attractive edge.

lovell-tiling

hi all you need to do is make sure all floor board have no movment in (if you have to replace any then do)you can use 6mm hardie backer board fix with flexable adhesive and grout
but use stainless steel trim on exposed edge

ormus

thats all i did with both my kitchen and bathroom. 6mm HB and tiled on top with flexible adhesive. been ok for about 2/3 yrs now.

lovell-tiling

hardie backerboard is different to hard board
hardboard is no good as it is so flexable
hardie backer board is cement based

latecomer

Thanks for all the replies. I'm going to get under the floor tomorrow morning and see just how bad the boards are but I suspect at least 20% of them are going to need to be removed, possibly more, hence why I was thinking of removing the lot.

Trouble is that as its the original tongue and groove then if any of the boards have excessive movement then I'm going to have to either pull up the surrounding boards or break off the tongues and hence wouldn't it be better to just replace the lot?