Wedi Tilebacker Board Query

[Pebble]

Hi, I am looking to install a Wedi Fundo shower tray by cutting out the chipboard and then securing 6mm ply on the joists (I will strengthen by adding more joists) followed by the tray. By fitting the tray on the joists + ply I don't have such an issue with levelling the rest of the bathroom since the Fundo tray is 40mm in height. It is the levelling of the rest of the room where my question lies. I intend to prime the existing chipboard and then secure 20mm Wedi Tilebacker board to the rest of the floor (using flexible adhesive), followed by electric heating matts. In order to bring the total level up to the height of the Fundo tray I may need to add a layer of screed onto the heating matt prior to tiling.

My question is whether it is ok to put the 20mm Wedi Tilebacker board straight onto the chipboard floor without first securing a layer of plywood ? Is the Wedi tilebacker strong enough to avoid having to first put Ply down.

Thanks

[Sir Ramic]

Moved to correct forum and deleted duplicate thread .

[Thespanishtiler]

you should be working to the preped floor height of the room as a level to set your fundo.

ie lift all the chip board
lay new flooring (ply)
overlay with cement boards (hardie backer)(or insulation boards)
allow for ufh and slc on top(6mm)
allow for ci matt if being used(4mm)
now set your fundo to this height (trimming of joists and counter joisting may be needed)
use min 12mm ply for counter boarding

once set as per mfrs instructions lay ufh and slc over to level of fundo threshold

lay ci matting

tape and tank as per products you are using

Tile

[Pebble]

Thanks. Can you let me know what thickness ply to use for the new flooring once the chipboard is removed. Also what should the thickness of the cement boards be on top of the ply ?

Sorry for my ignorance, what does "slc" stand for and "ci matt".

The fundo is 40mm high so are you saying I should put the Fundo on the new plywood (thickness tbc) + cement boards (thickness tbc).

I am worried about the step up into the bathroom if I set my fundo on the preped floor so is there any clean way of minimising the step up into the bathroom ?

[Thespanishtiler]

slc is self leveling compound (you need one suitable for ufh)

ci is crack isolation matting for decoupling the expansion and contraction of the ufh from the tiled floor

ply to be min 18mm with extra noggins at joints all screwed and sealed on the back and sides, 6mm cement boards laid ond spf and screwed.

the fundo sould be let down into the joists to be set at a level that correspondes with your prepped floor after the ply, cement boards, ufh, slc and ci are all laid.

hard to explain the ins and out of wetroom prep and to be honest i would recomend a local pro did the work for you.

off out now so wont be on line

[Thespanishtiler]

also re my 1st post you should lay the slc to a level that corresponds with an allowance for laying the ci on a bed of spf so it is dead level with the fundo threshold once down.

[Pebble]

Great thanks for clarifying that. So it seems that it is ok to lay the fundo tray directly onto the joists (assuming I add counter joists for strength).

[jay]

Try this http://www.google.com.au/url?sa=t&so...b1Hcz5iJfYGx2g

[Thespanishtiler]

Great thanks for clarifying that. So it seems that it is ok to lay the fundo tray directly onto the joists (assuming I add counter joists for strength).

no it is not !!!

You have to have counter joists set to carry 18mm ply interspersed between the joists so as the ply is level with the height you have trimmed the joists down to. trimming is needed sometimes so as the fundo threshold is at the level you are preping the main floor level up to.

try reading the literature on fitting the wedi fundo, the supplier you are using will provide this for you

[Dave]

IMO you should not be trimming joists..?..

You can get trays that are now only 22mm thick and span the joists without the need to board out between the joists for support.

But you deffo DO NOT trim joists down in thickness/depth etc..

[Thespanishtiler]

IMO you should not be trimming joists..?..

You can get trays that are now only 22mm thick and span the joists without the need to board out between the joists for support.

But you deffo DO NOT trim joists down in thickness/depth etc..

IMO timming say 6 mm off the top of a joist then running 3''x2'' along both sides screwed at 75mm through from both sides is no issue what so ever.

I am well aware of and used most of all the tray formers available on the market and would in such a case use say a shower stone or showerlay former BUT this guy specified he was to use a fundo former so I have offered my advice as such.

if he wants he can slap it straight to the floor and lay 40mm wedi all round but the door step may not be too attractive.

lets do the maths

floor 22mm

hb board on spf 8mm

ufh in slc 6mm

ci on spf 4mm

total 40mm NO NEED TO TRIM JOISTS

above scenario without ufh and slc

Total 34mm TRIM 6MM OFF JOISTS

If you where to overlay a 22mm floor with hb on spf and lay ufh in slc with ci on top you would have to raise your 22mm former by 8 mm to get a level threshold

the choice is yours

[Thespanishtiler]

and another point

its very rare to find the joists under your tray location are all level and true so are generaly not so usefull to fix direct to unless you want a tray that drains away from the gully

[Dave]

Each to their own Rob.. .. but when i trained in C&G joinery as a Teen , you never trimmed joists like that.. .. if joists are different levels for a tray to sit flat then you frame the insides of the joists to level up.. Taking depth from joists is weakening them... but if it works for you then that is great.. ..

I agree that a tray does need to sit flat and true for flow rate on the tray drain.. these 40mm trays are old school now IMO.. plenty other options to keep heights down...

[Thespanishtiler]

the point is dave that by trimming lets say 5mm off a 150mm x 50mm joist over 900mm length you loose 3.33% of its volume
by adding 2 new 3'' x 2'' joists at either side you then increase it by 75 %

0ver 50 wetrooms installed and never a failure or a call back

more than happy with my working practices cheers

and so are my many clients

[Dave]

Ahhh you didn't say you were adding strengthening after trimming you sly devil you.....

[Thespanishtiler]

[Pebble]

Thanks guys for your help with this..