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Our en-suite and main bathroom will both be wet rooms.

 

I have identified the wet room formers for the 2 shower areas, they are 22mm thick, but for reasons of budget (lack of) I am not buying them yet.  I do however want to floor most of the rooms.

 

So what 22mm thick floor boarding for a wet room, suspended on Posijoists at 600mm centres?

 

Is it as simple as P5 chipboard, or something more exotic?

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I'd have thought so then tank TF out of the wet room area.

Edited by Onoff

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18 T&G OSB and 6mm Aquaboard = 24mm. Very close in depth to the 22mm tray. Tank this and then you've a great base for the tiles. 

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I assume you are putting porcelain/stone tiles on the floor. In which case surely some wbp plywood (or whatever it is called nowadays) would be ideal for the job. Or Marine ply if you want it to be bombproof, belt and braces.

 

You can get 22mm ply, but will take a lot of phoning round and probably cost more than 25mm which is widely available.

 

You might even appreciate the 3mm when you come to fix the wetroom former in to place

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18mm T&G chipboard is no good for 600 centres, only for 400 so can't use that.

 

Do I NEED plywood? Last house has tiles onto chipboard with no issues (slate in the hall, ceramic in the kitchen) Probably just using some form of ceramic tiles on the floor pf these rooms, a long way from that decision yet.

 

I was assuming that whatever tanking I use would waterproof it, that is a question I was going to leave until we are ready to do it but I assume we are talking about something you paint on, rather than a sheet of something?

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2 minutes ago, ProDave said:

18mm T&G chipboard is no good for 600 centres, only for 400 so can't use that.

Who suggested 18mm T&G chipboard? I suggest 18mm OSB as it's thinner, will span 600mm and cheaper than ply.

Edited by Dudda

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12 minutes ago, Dudda said:

Who suggested 18mm T&G chipboard? I suggest 18mm OSB as it's thinner, will span 600mm and cheaper than ply.

Sorry missread that.  That's a possibility.

 

Do you have a link to the Aquaboard you are suggesting? I googled it and it came up with Aquapanel but that's flippin expensive. Is that what you meant?

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6 minutes ago, ProDave said:

Sorry missread that.  That's a possibility.

 

Do you have a link to the Aquaboard you are suggesting? I googles it and it came up with Aquapanel but that's flippin expensive. Is that what you meant?

Aquapanel is by Kauf and just an example of a cement board. Any cement board will do and they usually come in 6mm thickness for floors and 12.5mm thickness for walls. I think @Onoff is using something similar in his famous bathroom on the walls and I intend to use them in the next few weeks. They aren't cheap but if its for a bathroom you usually only need a few square meters and you don't want any movement which could crack tiles. My shower tray is due for delivery on Tuesday and I'll need 5 cement boards at about €14 each to cover the whole WC floor. Have the OSB down but not the last sheet beside where the tray will go.

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I will have a total of 12 square metres for both rooms, a bit less of I miss out using aqua panel under the bath (that bit won't be tiled either)

 

I take it you glue and screw it to the OSB (with a lot of screws)?

 

Like you I'm planning to lay most of of the floor, leaving the boards that adjoin the shower tray loose to be cut to final size later.

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5 minutes ago, ProDave said:

I will have a total of 12 square metres for both rooms, a bit less of I miss out using aqua panel under the bath (that bit won't be tiled either)

 

I take it you glue and screw it to the OSB (with a lot of screws)?

 

Like you I'm planning to lay most of of the floor, leaving the boards that adjoin the shower tray loose to be cut to final size later.

Ya, you can use adhesive and screws to fix it to the OSB. I've OSB everywhere upstairs so it was easy for me to continue it into the WC. This is the one I'm looking at in Ireland. Only €72 total which is about £63 for peace of mind. https://www.tiles.ie/tile-backer-board-cement-backer-board 

So you'll need a good bit more even without under the tray and bath but it's the best and strongest job you can do. As it's cement board it will be more durable than ply in damp conditions. Chipboard would probably be ok but I don't know if I'd risk it. Ply will be good enough and cement board will be better again. It's another one of those cost decisions everyone has to make daily.

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Forget chipboard, bodgit and scarper wouldn't use that in a bathroom.

 

 

The difference in price of 18mm OSB and 25mm wbp ply is probably £15 a sheet (8'x4') cement board will be more work (as its 2 lots of glue and screws) and money, marine ply more money again, but less labour

 

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3 hours ago, Dudda said:

18 T&G OSB and 6mm Aquaboard = 24mm. Very close in depth to the 22mm tray. Tank this and then you've a great base for the tiles. 

Only if the joists are at 400mm centres ;). If they're 600mm centres then you need 22mm deck min. 

Edited by Nickfromwales

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Think I'd rather do 22mm V grade chip and tanking with tanking tape round the edges where walls meet floor etc.

 

But if going the other route I found this that's 1200x800x6. Cheaper than others that are 1200x600x6:

 

https://www.crowntiles.co.uk/hardiebacker-250-ez-grid-cement-board.html?utm_source=google_shopping&gclid=CPiN_rKU99QCFRQ6GwodDugPhw

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27 minutes ago, Nickfromwales said:

Only if the joists are at 400mm centres ;). If they're 600mm centres then you need 22mm deck min. 

So what's your recommendation?

 

As Posi joists are a lot fatter than standard joists, the "gap" between joists is 500mm.

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Current job has existing 22mm P5. As it's got ( rather poorly fitted ) I-beams at 600mm centre I've decided to use 22mm P5 plus 9mm ply as the binder. 

 

Pic of former sat on the floor so I could mark the plywood support sections to cut out the linear waste footprint. 

IMG_5829.thumb.JPG.d40a953b8e7d8bd83d9579a044b58e23.JPG

 

Pic of the local support plywood. The 40x40mm battens were used to fit engineered, full depth noggins out of 18mm ply ( made by me bespoke to suit ) as the original builders thought that noggins were unnecessary :/  

IMG_5830.thumb.JPG.b3d4a486e845ad1fc110ace25e3f2061.JPG

 

Pic of the PU glue which I smothered everything with prior to fitting a tray sized piece of 9mm ply down and screwing on 100mm centres. Then the tray went down with Sikaflex EBT and screwed through the pre marked fixing locations on the tray. Zoom in and you'll see the circles where you drill through the grp to create screw holes. 

 

IMG_5834.thumb.JPG.1b8a4e0761a6a3e2cbfb3f664a40bd8e.JPG

 

A pic of the tray 9mm proud of the new P5 floor, which will be ply'd next to create a flush floor. The screws hold the tray down whilst the SFlex goes off, then one at a time I'll remove each screw, countersink it, pump the hole full of SFlex and send the screw back in snug, not too tight. 

 

image.thumb.jpg.31855cf6fa0c40a640c6c7742b73117d.jpg

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18 minutes ago, ProDave said:

So what's your recommendation?

 

As Posi joists are a lot fatter than standard joists, the "gap" between joists is 500mm.

All I can say is it's cheaper to buy thicker wood now than lift a floor later ;). It's not a place to economise imo, but I do go overboard TBH as it's my business on the line. 

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1 hour ago, Nickfromwales said:

Only if the joists are at 400mm centres ;). If they're 600mm centres then you need 22mm deck min. 

No... BS: 8103-3 says 600mm centres for 18mm OSB 3 T&G. Chipboard; then yes you need thicker but not OSB. The bending, tensile, compressive and shear strength of OSB 3 are stronger than chipboard as can be seen in BS EN 12369-1.

 

If you're worried go for thicker but 18mm OSB is fine in a domestic situation.

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22 minutes ago, Dudda said:

No... BS: 8103-3 says 600mm centres for 18mm OSB 3 T&G. Chipboard; then yes you need thicker but not OSB. The bending, tensile, compressive and shear strength of OSB 3 are stronger than chipboard as can be seen in BS EN 12369-1.

 

If you're worried go for thicker but 18mm OSB is fine in a domestic situation.

Ok, admittedly don't use osb so can't vouch for how it 'feels', so thanks for the nudge. :)

I just don't like the way screws behave when driving them into osb so I've never considered it a contender for tiled floors as the screw purchase is of paramount importance afaic. Others have stated that builders have just laid the boards on glue, but how can they stop them lifting as the glue foams and cures :S ?

The difference between 22mm and 18mm is immensely apparent when waking around a room with 600mm centres, so my advice is go for 22mm and sleep well. 

?

 

 

Edited to add : 

"Not lost a patient yet", but been to loads of others where I've had to rip it all out, beef up the floors and redo it all ;)

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So my choices seem to be:

 

18mm OSB then 6mm aqua board, almost matches shower former thickness with shower former laid direct on joists (with additional supports)

 

Or, 22mm V5 chipboard with 9mm ply laid on top.  9mm ply also laid on joists under shower former so they are both the same depth and to give additional support to the tray.

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You can easily go 22mm and 6mm if you want to shave another 3mm off.

With what's been said, even 18mm osb and 6mm ply will suffice. What's the thickness of the flooring the room meets at the threshold?

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Both the bathroom and en-suite adjoin rooms with 22mm chipboard and then carpet.  Keeping the overall thickness to close to 22mm plus tile thickness will give a near level transition.

 

I am trying to make it as simple as possible so at the moment 22mm V5 and 6mm or 9mm ply sounds simplest, but what is such a thin bit of ply going to do? I still can't see what's wrong with the tanking membrane straight onto the 22mm V5? addinf a thin later of ply just seems to add a lot of glue and screws for no additional strength, and surely the tanking membrane is waterproof enough?

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Tiling directly onto the deck is the biggest no-no in the history of tiling. The ply is used to bridge all the board joins and bind the floor, preventing lateral movement and the grout from failing. ;)

Another option is to lay ditra mat ( the decoupling membrane ) and tile onto that. You'll only gain 4-5mm back though and it's not the easiest thing to lay. You have to get the adhesive like gum so the mat sticks to it and stays COMPLETELY stuck down and flat. 

I think I'd go 18mm OSB3 and 6mm ply to keep your threshold low. ?

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But the tanking membrane you linked to ear;ier, this one http://www.impeyshowers.com/waterguard says:

 

Only 1mm thick with superior De-coupling properties of 10mm
Economical and safe - no need to buy a additional decoupler

 

If I have to fit something over the chipboard, then the aquapanel sounds a lot better, nice and solid. I just can't get it out of my head that 6mm ply is flimsy, and would only "work" in my mind if you clued it down with a 100% bed of adhesive like spreading tile adhesive over the floor to stick it 100% with no voids?

 

Have I just been lucky with my old house, 17 years of tiles glued direct to chipboard with no issues?

 

18mm OSB and 6mm ply sounds the easiest but I can't get over my mind saying it has to be 100% glued or it will flex?

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So.... I've used 22mm T&G Egger that's glued and screwed (against MIs..!) and then put floor heating set in latex self leveling compound  and Fiberglass scrim into the SLC in an ensuite. Tiles on top and nothing moved in 10 years so far but I wouldn't want to use it over a larger area. 

 

It it does sound counter intuitive but 6mm ply does make a big difference assuming it's properly glued and screwed. 

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