Morning all,

First query on this forum, so here goes!

Renovating my own property at the moment and have finally reached the time of thinking about the bathrooms.

Have decided to go for wetrooms in both an ensuite and main bathroom, and have gone down the aquadec route, both rooms using 1000mm sq tray.

Opening question then! regarding floor prep, It's an old house with 22mm floor boards and i'm reflooring both areas in and around the rooms. so was thinking of flooring the bathroom areas direct to joist with 22mm ply, which maches both my floor boards and aqua dec for height.

Is this thick enough? how often should i be screwing it down? is it worth gluing it down?


Hoping the above makes sense

Cheers

Sim

That thickness will be ok as long as there is no deflection after its fitted. If there is any deflection in the existing floor you should add some extra niggins to tighten it up. The ply should be fine then. Id screw it down at least every 150mm as you only have the joists to screw it to. I wouldnt glue it down as i dont see you will gain anything from it

Originally Posted by Scottley

That thickness will be ok as long as there is no deflection after its fitted. If there is any deflection in the existing floor you should add some extra niggins to tighten it up. The ply should be fine then. Id screw it down at least every 150mm as you only have the joists to screw it to. I wouldnt glue it down as i dont see you will gain anything from it

I'm in a similar situation with a 22mm tray former laid onto the joists. Is there any need to put a decoupling layer onto the plywood? If so then I had thought of using 18mm ply with a decoupling layer and underfloor heating matt, ie. ending up around 22mm.

Thanks Scottley, always good to be re assured, now to wade through the pro's and con's plasterboard versus hardibacker!

Originally Posted by Sim101

Morning all,

First query on this forum, so here goes!

Renovating my own property at the moment and have finally reached the time of thinking about the bathrooms.

Have decided to go for wetrooms in both an ensuite and main bathroom, and have gone down the aquadec route, both rooms using 1000mm sq tray.

Opening question then! regarding floor prep, It's an old house with 22mm floor boards and i'm reflooring both areas in and around the rooms. so was thinking of flooring the bathroom areas direct to joist with 22mm ply, which maches both my floor boards and aqua dec for height.

Is this thick enough? how often should i be screwing it down? is it worth gluing it down?


Hoping the above makes sense

Cheers

Sim

As you are taking up the floor anyway I would put extra noggings in as scottley has already said, you want to put them in at 300 centres. as the floor will be open it is better to make sure now rather then screwing down the ply and finding out there is still movement there. you could use 18mm ply and put a 6mm backer board on top of the ply and install the tray to suit the height.

Originally Posted by dumbrill

I'm in a similar situation with a 22mm tray former laid onto the joists. Is there any need to put a decoupling layer onto the plywood? If so then I had thought of using 18mm ply with a decoupling layer and underfloor heating matt, ie. ending up around 22mm.

you have a 22mm tray

ply 18mm
heating mat 3mm
slc 1mm over top of cables approx
adhesive to stick de-coupler 2mm
de-coupler 3mm
27mm in total approx. leaving tray 5mm aprox below finished surface before tiling. could raise tray by 6mm by putting tile backer under it.
What tiles are you using?
depends on tiles and area but you might not need a de-coupler, you could use a tile backer board.

18mm ply
6mm tile backer board
heating mat 3mm
slc over the top of cable 1mm
adhesive and tanking membrane 2mm
total of 30mm - tray 22mm = 8mm needed to bring tray up could put some 9mm ply under tray to raise tray to get the height right.

Originally Posted by peckers

you have a 22mm tray
ply 18mm
heating mat 3mm
slc 1mm over top of cables approx
adhesive to stick de-coupler 2mm
de-coupler 3mm
27mm in total approx. leaving tray 5mm aprox below finished surface before tiling. could raise tray by 6mm by putting tile backer under it.
What tiles are you using?
depends on tiles and area but you might not need a de-coupler, you could use a tile backer board.
18mm ply
6mm tile backer board
heating mat 3mm
slc over the top of cable 1mm
adhesive and tanking membrane 2mm
total of 30mm - tray 22mm = 8mm needed to bring tray up could put some 9mm ply under tray to raise tray to get the height right.

Thanks for the quick reply.
The area of the ply is about 1.7m x 1.6m - does this affect the need for a decoupler?
Do I need a decoupler if I'm going onto ply? The OP of this thread hasn't indicated that he's going to use one.
I haven't chosen the tiles yet. How can the choice of tiles affect whether I need a decoupler?
I would much prefer to keep the depth down so dispensing without any unnecessary layers would be good.
As a bit of background I should probably explain that my floor is made up of welded 50x50mm rectangular hollow section steel stood onto the concrete slab under the ground floor. The biggest opening between 'joists' and 'noggings' is 52 x 34 cm and the whole structure is very solid. I plan to screw the ply directly onto the steel using self drilling screws.
I've got the 1.7m x 1.6m section sloping down (1:70) towards a Purus Maxxus floor former at one end. The only weakness in the design is that the door is halfway along the side of the room and so I don't want to build the wetroom level up too much above the outside level. Although the door will be away from any water source.
I've attached a picture.

well ive never tiled onto anything fitted to a steel frame before and this is new to me.
If you were using a natural stone tile with undertile heating then i would advise using a de-coupler as this is intended for laterall movement as when the tiles heat up. If using ceramics/porcelain over that area i wouldnt be to concerned about using a de-coupler. You will however have to waterproof the ply and this can be done by installing a membrane such as schutler kerdi membrane.
the method would normally be ply heating matt slc membrane and then tiles.

But i must say i havent tiled onto a steel structure before and dont know if any other considerations should be taken into account!!!!!!
There may be another forum member on here who has done so who could give advice.
Or you could contact wetdecs who is a forum sponsor and supplies all materials for wetroom installations. you will find his ad on the main start up page on the left hand side.
I hope this helps but as i said i havent come across this type of installation before and i dont want to give you the wroung info...

Id put some thought into the expansion and contraction of the steel frame, if it was mine id definitely use a decoupler with any type of tile

Originally Posted by peckers

well ive never tiled onto anything fitted to a steel frame before and this is new to me.
If you were using a natural stone tile with undertile heating then i would advise using a de-coupler as this is intended for laterall movement as when the tiles heat up. If using ceramics/porcelain over that area i wouldnt be to concerned about using a de-coupler. You will however have to waterproof the ply and this can be done by installing a membrane such as schutler kerdi membrane.
the method would normally be ply heating matt slc membrane and then tiles.

But i must say i havent tiled onto a steel structure before and dont know if any other considerations should be taken into account!!!!!!
There may be another forum member on here who has done so who could give advice.
Or you could contact wetdecs who is a forum sponsor and supplies all materials for wetroom installations. you will find his ad on the main start up page on the left hand side.
I hope this helps but as i said i havent come across this type of installation before and i dont want to give you the wroung info...

I won't be using natural stone because I don't want to bother with the sealing, etc and I'm planning to put a membrane over the ply. I guess I'm looking for the thinnest/best membrane and heating combination and the right ply thickness.

Originally Posted by Scottley

Id put some thought into the expansion and contraction of the steel frame, if it was mine id definitely use a decoupler with any type of tile

im just picking your brains here scott a decoupler in this type of install is wise as you say do you think the steel frame could be affected for expansion by the heating cable more then if it was a normal wooden joists??

Hindsights a wonderful thing. You could have had a wet ufh system laid in a screed to build the floor level up and incorporated the falls for the tray into the screed

I would contact the technical dept, at either Schluter or Dural both of them are manufactures of de-coupling membrane systems. Better to get their advice imo

Originally Posted by Scottley

Id put some thought into the expansion and contraction of the steel frame, if it was mine id definitely use a decoupler with any type of tile

The rate of expansion of steel is not very much. About one thousandth of a percent change per degree. Along a length of 1700mm and with a 20 degC temp rise the steel will expand by 0.4mm. I'm assuming that this is negligible.

I really dont know steve, the steel will certainly expand and contract more than timber joists but how that affects the ply i have no idea.

Originally Posted by Scottley

Hindsights a wonderful thing. You could have had a wet ufh system laid in a screed to build the floor level up and incorporated the falls for the tray into the screed

I considered this, but in reality all that I loose is the thickness of the heating membrane.

Originally Posted by dumbrill

The rate of expansion of steel is not very much. About one thousandth of a percent change per degree. Along a length of 1700mm and with a 20 degC temp rise the steel will expand by 0.4mm. I'm assuming that this is negligible.

Having looked further the coefficient of expansion of concrete is not much different to that of steel - depending on mix, see attached jpg. The figure for steel is around 10 x 10-6/degC. Therefore a steel subfloor or a concrete subfloor is not really an issue.

Personally id have gone for the concrete as the ufh is cheaper to run than the electric system. But its not mine it yours

Id still be inclined to go for the decoupling membrane as there is still room for movement in all directions.

I would still contact the manufacturers of the products you are using to make sure there suitable

As you are taking up the floor anyway I would put extra noggings in as scottley has already said, you want to put them in at 300 centres. as the floor will be open it is better to make sure now rather then screwing down the ply and finding out there is still movement there. you could use 18mm ply and put a 6mm backer board on top of the ply and install the tray to suit the height.

Noggins make sense, but whats the advantage of backer board over a thinner sheet of ply? room will be tanked using the membrane from the Aquadec kit.

On another note I presume I have no need for a decoupling layer in this situation as, unlike dumbrill, i have no plans for underfloor heating in either area

You can go either way using tile backer or not, I was only offering an alternative as a tile backer board is a better substrate to tile onto and if it was me doing the job for you then this is the way i would recommend, fitt the membrane as per manufacturers instructions and you will be fine.

Impey under board their trays in the install videos to strengthen them........

[ame=http://www.youtube.com/watch?v=3xekpG9Y22k]YouTube - Impey Aqua-Dec Wetroom Installation Guide Part 1[/ame]

Thanks Wetdec,

while your here, would you recomend the dura -wp system that i see talked about on the forum to go with the impey tile safe membrane system?

if so, which order would you use them? i.e floor first or walls first

Cheers

Sim