Godley

Some advice on floor tilling

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Hi, this is my first post so be gentle please.

I'm about to start tilling the bathroom floor and although I've some experiance tilling walls, this will be my first go at a floor.

 

The first problem I have is how high the bathroom floor would be if I had to glue and screw over the floorboards and then use either a backer board or Ditra matting (yes I've read some of the other threads before posting :) )

 

The gap between the top of the bathroom joists and the bottom of the batroom door / landing carpet is 32mm ish so I could probably eek that out a bit more without it looking too much of a step up.

My tiles are 8mm thick and if I go with 6mm adheshive and 2mm back butter I'm left with 16mm to put plyboard and anything else thats needed down.

 

My question I guess is that if I were to remove the floorboards could I just put ply straight onto the joists without it causing any issues and what would be best, going with an 18mm ply and tilling straight on top of it or getting a 12mm ply and using Ditra/backer on top.

 

Thanks for any help you can give me and I hope there's not too many people just shaking their heads at me

 

Chris.

 

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1 hour ago, Godley said:

...

Thanks for any help you can give me and I hope there's not too many people just shaking their heads at me.

Welcome. As to shaking of heads, there's more shaking of heads when when members don't research what we've already posted on this forum. So thanks very much for having done a bit of research before posting here.

 

By the way you lost me me as soon as you mentioned bathroom floor height. The only tiling I've ever attempted has been at night if you understand me. I suppose both forms of tiling for me would end with a massive headache.

 

Good luck.

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From what I've read you need more like 22mm plywood over joists before tiling. I think 18mm is the minimum for Building Regs. 

 

You may also need to beef up the floor joists and add noggins to reduce movement before screwing down plywood on 200mm centres. The ply must be sealed before tiling. 

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PS We have a small difference in levels at our bathroom door between a stone floor in the bathroom and wood floor outside. It's not been an issue although our step is going up as you leave rather than enter. The step is about 10mm high.

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I'm not saying it's right or wrong, but I've done exactly what you've suggested a few times. Pulled up floor boards and laid 18mm OSB down straight onto joists, screwed down. Then tiled straight onto the OSB board with flexible adhesive. I've never had an issue and my bathroom floor has been down 15+ years.

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What is the floor presently?

 

I have 22mm P5 chipboard, an Impey Waterguard membrane (it's a wet room) and tile onto that.  The Impey membrane is a decoupling membrane that makes it okay to tile onto chipboard and has negligible thickness.

 

The tiles are probably about 15mm above the flooring max, about right to meet with a carpet and underlay at the door.

 

P.S.  Before I was told such things are wrong in a previous house I tiled the hall and kitchen direct onto bare P5 chipboard with a flexible adhesive and never had any problems in 17 years.

 

 

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1 hour ago, Vijay said:

I'm not saying it's right or wrong, but I've done exactly what you've suggested a few times. Pulled up floor boards and laid 18mm OSB down straight onto joists, screwed down. Then tiled straight onto the OSB board with flexible adhesive. I've never had an issue and my bathroom floor has been down 15+ years.

You're very lucky in that case.

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13 minutes ago, Nickfromwales said:

You're very lucky in that case.

 

I've done a few floors that way and never had any issues. What's the reason you think that?

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11 minutes ago, Vijay said:

 

I've done a few floors that way and never had any issues. What's the reason you think that?

Due to the very high number of cracked tiles to fully failing floors that I have seen / had to re-do over the years. I always fit a plywood layer or a decoupling membrane in these instances ( over joists + timber deck ) and have never had one fail.

The highest fail rate has been on poorly affixed P5 which has been nailed down, so maybe your diligence with how you fix the deck down prior to tiling / noggins on joints maybe (?) has been the key to your individual success. Others I've come across have at least had tiles which have cracked in the location of the deck board joints, or worse.

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I've honestly never had a cracked tile and I can think of at least 5 floors I've done that way. I screwed down the OSB every 400mm so maybe that helped. I just always assumed using flexible adhesive was the key but I'm always happy to learn :)

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1 hour ago, ProDave said:

What is the floor presently?

 

 

 

 

20mm floorboards with 12mm ply loosely screwed in over that and finally covered with a wood effect vinyl. :(

Everything feels loose underfoot like the boards are just resting on the joists. I pulled up the vinyl and it looks like a poorly made jigsaw that doesn't fit together.

 

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1 hour ago, Nickfromwales said:

I always fit a plywood layer or a decoupling membrane

In your opinion then, if I was to use a 4.0mm Durabase CI matting would I be able to use 12mm ply? How thick does the adhesive need to be between the matting and the ply?

The video's I've been watching all seem to show quite a wet looking layer of adhesive so does that mean it would end up not much thicker than the actual matting?

Thanks

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12mm directly on joists doesnt meet building regs let alone the stiffness needed to stop tiles cracking...

 

https://ukbathroomguru.com/screwing-down-structural-plywood-to-joists/

 



I would recommend a minimum of 22mm thick external WBP or marine ply.If your joists are widely spaced with few noggins (over 400mm apart) then I would recommend you use 25mm ply (if you can source it) as this will help to limit deflection.

 

https://www.diynot.com/diy/threads/minimum-thickness-of-ply-subfloor.511459/

 



The absolute minimum thickness you can use on 400mm/16in centres is 18mm. Never heard of flooring being done with anything thinner.

 

 

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1 hour ago, Temp said:

12mm directly on joists

 

11 hours ago, Godley said:

20mm floorboards with 12mm ply loosely screwed in over that

Think that means 12mm binder over floorboards, then decoupling membrane. @Godley?

If the 12mm ply is over properly fixed floorboards and that has been screwed and glued then you can tile straight onto that as long as you fully bed the ply and butter the backs of the tiles. 

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+1

12mm ply over existing 20mm floorboards would be ok if screwed down properly.

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what do you guys do about the raised height though, a small step into the room?

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