Edge problem replacing floorboards

[2hapennies]

Hi all,
This is my 1st post on this great forum, hope you can help.
I want to ceramic tile the bathroom floor, currently floorboards. Originally I intended to put 6mm backer of some sort over the top, and found this forum while looking for best practice. However having read a number of threads on this, I then thought the best thing would be to replace the boards with 18mm/20mm ply first. But down both sides of the room the existing stud walls are offset from the floor joists which run parallel. Ie. the walls are just standing on the floorboards between 2 joists. So I cant replace the boards between the walls and the nearest joist, so would have to do some sort of patching, yuk. I reckon this must be quite common, anyone got a solution? Or should I just go back to putting thin backer down over the whole lot?
Its not a wetroom, I dont want to raise the floor level by much, the joists and boards are sound with little if any deflection, but a number of the boards are a bit warped/dished. Would 6mm backer be OK on these? I'd appreciate any advice anyone can give, Thanks, 2hP.

 

[diamondtiling]

Welcome to the forum

Just to clarify, are you saying that you cant cut out all the floorboards because of the walls?

 

[mikethetile]

your right, you cant take the boards up, this is bad building practice but they get away with it as its allowed under regs

you can overboard with backerboard or no more ply

its unfortunate that you cant brace the floor up either

 

[2hapennies]

Thanks Diamond. Yes thats right. The floor joist is about 20cm away from the wall which stands on the floorboards. The boards run under the wall to the next joist on the other side of it. So I cant cut the boards right upto the wall without undermining the wall structure and floor on the other side. Only possibility I can see is to lift boards at intervals on both sides of the wall, and fit noggins to support the wall, but seems way over the top ( or rather under the bottom!)

 

[2hapennies]

Thanks Mike, Yes I think I'm back to giving overboarding a go. But I really dont want to use anything thicker than 6mm, 'cos of step up in doorway, though I've read on other threads that people think 15mm should be minimum. As I said the floor is solid, its just the dished boards that concern me. Is the overboarding likely to crack where the dips are?

 

[mikethetile]

no more ply is 6mm thick and can be used in place of ply

how dished are your boards

 

[trevortine]

Hi 2hapennies, if you overboard with cement board then you apply a layer of single part flex to the existing floor first. Sit your boards over this an that will take up any voids. Most of the manufacturers state this in their installation instructions.

 

[2hapennies]

Worst are dished 3 maybe 4mm?
I've not looked at NMP. Is it cement based like Hardie, or foam based like Wedi & Marmox?
I'm wondering which type would be best - foam type to absorb the ripples, or cement based to span them?

 

[2hapennies]

Thanks Trevortine, what is 'single part flex' please?

 

[DHTiling]

Hardi bacler 250 ( 6mm).. you bed the floor first as trevortine stated and place the hardi boards into the adhesive bed and screw down every 200mm.. The adhesive will fill voids created in the dished out boards..

Bu you must make sure the floor is solid enough first before over boarding.

 

[mikethetile]

nmp is cement board like hardie

 

[2hapennies]

OK all, thanks very much for your help and patience.
I've now looked up NMP and SPF, and agree these look like my best bet.
I've found a thread on "whats the best SPF" so I'll have a look at that. NMP versus Hardie? Any views? or are they much the same?
Are there any incompatibilities between different SPFs and overboards? Thanks again, 2hP (Martyn).

 

[Rich]

I use NMP and think its great, but I think you should prob go with hardie for this one. NMP recommend using the NMP glue where as Hardie would say to use a single part flexi adhesive which IMO would do a better job at filling these dishes in the floor boards.

 

[2hapennies]

Thanks Dylante, having looked at the NMP instructions I'd wondered about their use of a 'small bead' of their glue approach, which wont fill the dips, so hardie & SPF it is! Thanks again all.

 

[trevortine]

Let us know how you got on buddy! Remember, every days a school day, learn something new and you'll know the next time, just quick point as well, if you ever have to lay a lot of boards then always stagger them, ie in a brick bond fashion, this prevents having four corners meeting and a potential weak point! Good luck!

 

[diamondtiling]

Thanks Diamond. Yes thats right. The floor joist is about 20cm away from the wall which stands on the floorboards. The boards run under the wall to the next joist on the other side of it. So I cant cut the boards right upto the wall without undermining the wall structure and floor on the other side. Only possibility I can see is to lift boards at intervals on both sides of the wall, and fit noggins to support the wall, but seems way over the top ( or rather under the bottom!)

Fitting extra noggins is not over the top, take up as much of the boards as you can and fit the noggins for strength, these noggins will then replicate the removed floor so the walls will not lose any integrity. You can then fit 18mm ply and hardi on top.
Reinforce under the wall as you go with your noggins, doing it a little at a time will relieve stress on the walls, do one joist and then another. The wall will not be load bearing if its sitting on timber.