Deflection issue with No More Ply down

[Deleted member 46792]

Hello

I am a DIYer and after a successful shower tile project set about tiling bathroom floor. Victorian terraced house, previous floor - exposed original floorboards. After research and consultation with a carpenter, I understood that the deflection wasn't bad and that I should screw down any loose-ish floorboards and overboard with 6mm No More Ply using the NPM mega strength adhesive. Having done this and having been pretty pleased with my efforts I asked a tiler (and paid for consultation services) round to give me his opinion. He said that my floor has too much deflection and that the grout and possibly the tiles will crack. He gave me a couple of suggestions - the most expensive being to start again and lay down 18mm ply. This could be tricky as I understand that even in the event of a nuclear war the NMP will probably still be sticking to the floorboards because of the strength of the adhesive. The other option he said was to get some expensive adhesive - bal single part fastflex I think it was - which has an elastic ingredient and get flexible grout that you can add an additive to that will make the grout very flexible.
This evening I have been wondering if it isnt possible to double up with overboarding with a layer of ply or another layer of NMP. I also did a test that I have read about which involves filling a glass of water and placing in centre of room and getting biggest person you know to jump about a bit. Well I fit that profile so I have done that and no water was spilt. I can see some deflection in the floor but I am not sure what to think now. I am not sure what is acceptable, what remedial actions to take..

Anyone got any thoughts on this? I dont want to do a cr*p job but I dont want to pull the house down!

 

[J Sid]

what size is the floor and what tiles are you wanting to fix?

 

[Deleted member 46792]

what size is the floor and what tiles are you wanting to fix?

Hi Julian, the room is 3m x 2.4m but there are bath, seperate shower tray and sink unit areas that wont be tiled. Its about 4.4 sq. metres of tiling. I have bought 60 x 30 porcelain tiles but they were cheap and would replace if something more suitable would go towards fixing the problem..?

 

[Kevbos]

Go over ply with 12mm ply screwed alot .use ditra mat or equivalent over this .tiles won't come up with a flexible adhesive and grout

 

[J Sid]

I would be very surprised if a floor has that much movement and if it has is it going to hold a bath full of water!
@Kevbos wouldn't 12mm hardie board be better and no need for ditra.

 

[Deleted member 46792]

I would be very surprised if a floor has that much movement and if it has is it going to hold a bath full of water!
@Kevbos wouldn't 12mm hardie board be better and no need for ditra.

Hi Julian, do you mean you doubt whether the deflection is significant? Would you agree with Kevbos that its probably an idea to add a further 12mm?

 

[Kevbos]

Might well be .usually floor flexes because joists bouncing .I just cover myself in instances where floor bouncing .

 

[J Sid]

not seeing the job, but if the floor boards have been screwed down and the nmp was laid, I would be surprised if a floor of that size had that much bounce. If you think it has then laying 12mm hardiebacker board as per the manufacturer instructions would help.

 

[Kevbos]

I lived in sweden 2 years .they use plasterboard on floors and tank it .can't get insurance on house if you haven't whose right ?

 

[Stef]

If there's bounce in the floor then how is Ditra going to help??
Issue should have been fixed before nmp was fixed.
Option I would choose is get yourself an elastomeric adhesive like the BAL you have been told about, you can make your own up with certain addys & additives & fix your tiles.
If it fails then you go back to the start.

 

[Kevbos]

Or strengthen the floor before you start to tile .like you should do over any floorboards .6mm ply is not sturdy enough .at least 12mm 18mm preferably should be used .and ditra was made for a reason

 

[Stef]

Or strengthen the floor before you start to tile .like you should do over any floorboards .6mm ply is not sturdy enough .at least 12mm 18mm preferably should be used .and ditra was made for a reason

Ditra wasn't made to take deflection!!

 

[Deleted member 46792]

I lived in Sweden too. They do a lot differently!

Ive been in again and looked at the bounce. You can definitely see the floor move but its mm rather than a cm. And im pretty big. And its in two small areas not all over.

Im going to try with the elastomeric adhesive. Thanks very much for all the help.

 

[Kevbos]

No but was made to help eradicate movement after preparing a floor properly

Good luck with the bal .just look up tiling overy floorboards .that 2mm will transfer into cracks

It will cost 100 pounds to strengthen floor why not just do that

 

[Deleted member 46792]

Good luck with the bal .just look up tiling overy floorboards .that 2mm will transfer into cracks

aaargh...the 6mm NMP was supposed to do the job..as far as i understood 6mm NMP was supposed to do the job of 18mm ply...

 

[Kevbos]

Yes alot of new ideas in world say and don't do old and tried methods

 

[Deleted member 46792]

It will cost 100 pounds to strengthen floor why not just do that

You're probably right, ill sleep on it. I suppose the other concern is then the height increase between floor and hall...but that should be fixable with a decent threshold...

 

[Stef]

No but was made to help eradicate movement after preparing a floor properly

Yes it was made to help eridacte movement,
It's designed to eradicate lateral movement not deflection.

 

[Kevbos]

Yes as I said it's made to go over timber floors prepared properly .as timber contracts and expands .it helps the flexibility

Edp go buy a nice bit of oak same width as door liner use that to take out height difference

 

[Stef]

It's made to go over any substrate that is going to have any lateral movement in it.
I've heard too many people say that Ditra is a saviour to all problems, too many people think it's for bounce in a floor & if people see it being written like this then they will assume it is.

 

[Kevbos]

Yet I said put another 12mm of ply down preferably 18mm first to strengthen floor .I use ditra.to assure strength sticking to a solid wood floor .

And as your preferred method of fixing problem .yes the adhesive will stick tiles and not come up .but because adhesive so strong tiles will only just eventually crack as they the weakest now

 

[Stef]

Yet I said put another 12mm of ply down preferably 18mm first to strengthen floor .I use ditra.to assure strength sticking to a solid wood floor .

He's already put down 6mm nmp, if the sub floor was prepped properly then I would have used 6mm Hardie backer & then tiled.
I don't tile to ply & wouldn't fit ply over the top to try & strengthen the floor.
I would rip it out & start again but an elastomeric addy takes up a lot of movement.

 

[Kevbos]

Some tilers love hardie backer .but as I said if you prep floor properly with right thickness of ply you get no issue

And good luck getting that stuck ply up to start again .we were trying to overcome a problem .by what he said floor needed strengthening .I gave a solution .that does work .

 

[Stef]

Some tilers love hardie backer .but as I said if you prep floor properly with right thickness of ply you get no issue

15mm ply overlay BS + Ditra.
6mm Hardie glued & screwed or
6mm thermal glued & screwed.
I will use the one that's not going to give me a step into the bathroom.

 

[Kevbos]

That's ok but he's getting over a problem

Floor bouncing

 

[Stef]

Floor bouncing

& that's why I stated Ditra isn't going to help.
If the floors bouncing too much then it needs sorted from the joists up.

 

[Dan]

That's ok but he's getting over a problem

Floor bouncing

Stop double posting. I'm fed up of merging your posts.

 

[Flintstone]

Controversial Kev is your new nick name.

I have over boarded many many bathroom floors with nmp and not had any problems. I would judge deflection with my eyes, if you can see any movement when your walking on it or lightly bouncing on it then it's probably not right, shouldn't see any movement. But if there is some movement it's only gonna be the joists.
Don't bother putting anything over the nmp it's a waste of time.

 

[Deleted member 46792]

So I really have three options: 1) The correct way - rip up the NPM which will probably also destroy the floorboards. Fix/strengthen the joists so no deflection and lay 12/18mm ply floor, overboard with NPM or Hardiebacker. Tile. Expensive, disruptive and will make me cry.
2) The risky adhesive option - bearing in mind that the deflection is minimal a very flexible adhesive might resolve the problem. Only time will tell. 2 or 3 tiles would be affected. One commenter suggests he doesn't think i have a deflection problem in such a small room.
3) The raised floor option - Ply or hardiebacker. Adds 2 cm to the height of the floor. Will it definitely stop bounce after all that effort?

I hope the answer comes to me in the morning...night all. Thanks for weighing in.

 

[Deleted member 46792]

Controversial Kev is your new nick name.

I have over boarded many many bathroom floors with nmp and not had any problems. I would judge deflection with my eyes, if you can see any movement when your walking on it or lightly bouncing on it then it's probably not right, shouldn't see any movement. But if there is some movement it's only gonna be the joists.
Don't bother putting anything over the nmp it's a waste of time.

Cheers for your reply...what do you suggest?