Level Access Shower Flooring prep - Please help :)

[Carlosmobile]

Hi Everyone

First time posting so looking forward to some friendly advice!

We are pretty competent DIYers and want to take on the challenge of DIY fitting a level access shower/wet room. It will have a pumped power shower and glass screens to keep water from going everywhere (so not totally open like a “proper” wet room). Its a small space so to be on the safe side we want to tank the entire bathroom (plus its good practice)

We’ve done a lot of reading online, forums etc. and we’ve read many posts in the archive but there’s a few things that seem to conflict at times and we’d like to be clear as to best practice (even if it means overkill):

1. We’ll use 25mm WBP plywood over the joists (staggered), with screws at 300mm intervals. We’ve seen some recommendations to screw at 200mm intervals and to glue the underside to the joists. Should we stick with 300mm and glue/no glue?

2. We’ve seen advice to seal the underside and edges of the ply but we’ve also seen (less so) advice to seal top side too. Is it ok to do the top side or will it affect the adhesion of the tile adhesive used to fix the backer boards (which will also be screwed down later)?

3. Because of the ply, backerboard, tile adhesives, UFH, and SLC the bathroom floor could be as much as 10-15mm higher than the shower former. To level this out should we lay 10-15mm WBP under the former so that its at the level of the rest of the bathroom when it comes to the tiling? Is there anything else we can do to keep former and rest of the floor at the same level – we had thought to lay UFH on shower former with rapidset covering the wires before tiling so this would make the height difference 5-10mm.

Tanking

4. Most people, installation videos, etc. tank under the UFH but we have seen some people advise tanking after the SLC has gone down. Can you do both or will the tanking affect the tile adhesive in any way?

5. To tank the backer boards (we will use a waterproof one like Wedi or Marmox) we’ve also heard a few different things:
a. use self adhesive waterproof tape on the joints,
b. use tile adhesive on joints, then bed waterproof tape and then apply another layer of adhesive and
c. fully tank e.g. with sheet/membrane or paint on gum.

The last one seems like overkill if already using (and paying) for waterproof backer boards – but we will do if best practice. The self-adhesive tape sounds too easy to be the best solution but we will use in a flash if you guys feel it’s as good as any other method.

Thank you all for reading this post and for your advice!

Carlos

 

[tictic]

what is the joist size/thickness/spacing/span.. first...
the room is it upstairs/downstairs...

what size of former are you fitting[width/lenght and thickness]...
what size off gulley/trap is it[45mm-75+]...your shower how much litres per minute is it giving out...

get your set out with the former first...where is it going/easy run for waste ect....

then the former thickness?...18mm+

then you will look into overboarding/tanking..ect

one step at a time,dont want to go into a long reply... get the preperation done first with the floor/former first...then look into overboarding/tanking ect..

 

[AdamCH]

1. 200mm probably okay but I tend to go 4" (100mm) no glue but lots of noggins between the joists. 25mm WPB should be more than enough but make sure the floor is rigid (no bounce) first.

2. Seal the underside and edges of the ply with tiling primer (not PVA). Theory is it stops moisture being absorbed into the ply and expanding it. Seems more theory than reality to me but it's easy to do so ....

3. You can lay the UFH & SLC into the former. You can also raise the former with ply or backer board. A cement board might be better than a foam one for this unless the load is well spread.

4. Use Ditra or Durabase C++ over the SLC & UFH to waterproof & protect the tiles from movement.

5. Wedi and Marmox are waterproof and don't need tanking if you seal the joints properly. Just follow the manufacturers instructions on sealing the joints etc. You usually set the waterproof tape into tile adhesive or they may have a proprietary cement. Ditra and Dura do a corner tape for sealing floor to walls.

Others with more experience may be able to help you more.

 

[ziggy1979]

I'm far from a pro but I thought that the backer boards (set in adhesive and screwed) would work like a decoupling layer/membrane? If so Ditra etc should not be needed.

 

[Carlosmobile]

Hi Tictic

Thanks for your reply.

We've just moved into the property and the bathroom floor is carpeted. Ive not had a chance to take it all up so I don't know the joist sizes, spaces, directions, etc. I'm hoping to get started after the holidays so was wanting to get things straight in my head before then.

The room is upstairs (above the kitchen).

We were thinking of buying the Impey Aqua Dec Linear 2 (1200x900x22mm) which brings a drain (LinearFlo drain). Together they seem to be able to drain about 40l/min. We will be re-plumbing the entire bathroom so will use 40mm waste for the shower. Exact pipe run will need to wait until the floors come up and we see joist runs though.

The shower will have a pump (3-4 bar) on a gravity fed system (eventually we hope to get a second shower in an ensure in the loft off the same pumped supply). The rest of the house will be served hot water from the combi.

With the tray being 22mm thick if we use 25mm ply with 6mm waterproof tile backers set in a few mm of adhesive (these would both help tank floors and most importantly as insulation for UFH), the floor level will be about 10-15mm higher than the former. That's why we thought to have some ply under the former if possible.

Thanks

 

[Carlosmobile]

Hi AdamCH

Thanks for your post.

1. 100mm it is - the more screws the merrier . Will check for deflection but it seems very solid. But if I need to, will sistering the joists be the best way to help with deflection? - can't add support from beneath.

2. Thanks will do - any reason for not sealing the top?

3. Thanks

4. So it's best to tank above the UFH? If we use wedi/marmox type boards under the UFH and seal the joints would you still advise tanking above UFH - painting that gum stuff if cheap and easy enough...

5. Thanks. Will look at different companies to see what options they have. The self adhesive tape seems like a (quick) breeze. Btw has anyone heard/used of Jackoboard (http://www.tradewetrooms.com/6mm-jackoboard-backing-board-for-tile-1200x600mm.html?gclid=CIDfjbPV5LoCFVMRtAodX3QALw).

It looks like Wedi boards, etc but cheaper.

Thanks!

 

[AdamCH]

I'm far from a pro but I thought that the backer boards (set in adhesive and screwed) would work like a decoupling layer/membrane? If so Ditra etc should not be needed.

Decoupling membranes are different - they are a deliberate weak link to isolate the tiles from lateral movement in the floor beneath.

 

[AdamCH]

Ply priming - Couldn't tell you 100% but I think priming back and sides is part of the British Standards to slow down moisture ingress. Not needed on top because it tiled.

Ditra/Dura C++ isn't just tanking it's a decoupling membrane. The UFH will expand & contract the subfloor & the decoupling will help prevent it damaging the tiles. It also waterproofs so will useful to prevent water soaking into the SLC.

Jackoboard, Wedi, Marmox, Orbry - all do the same job. Make sure you use 10mm min on floor to get any insulation effect. You'll probably need 12.5mm for walls (for strength)

Cheaper here - http://www.insulationexpress.co.uk/...x-Multi-Board---The-Original-Marmox-Board.htm

 

[Carlosmobile]

Hi Adam

Thanks again! With the Dural/Ditra, it will add a few more mm to the flor height. Is there any way of using it but changing anything else to keep height in check - concern is the size of the step out of the bathroom.

Also, would the Ditra/Dural go over the SLC in the shower former?

Thanks

Ps - thanks for the link.

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[Carlosmobile]

Just read a couple of posts on another site advising that a 2mm gap be left around all plywood boards with 5-10mm at walls. I thought you should butt them together (read elsewhere to glue joints and use T&G if possible) with a 10mm gap at walls. Is either way fine or is one better than the other?

Thanks you all again!

 

[tictic]

when overboarding with wbp ply always place a 2p coin between boards and yes min 10mm around the perimeter of the room...

once you get your floor lifted...then you can look into what needs done until then its all guess work...

 

[Carlosmobile]

Hi Tictic

Thanks again mate! Will carry on reading, etc and will pick up this thread once the floors are up in Jan!

One last question but on the walls this time ...two walls are external. I thought to remove existing tiles, knock back to brickwork and level out with treated wooden studs then board with backer board, seal joints and tile.

Question is about condensation. I'd like to insulate in between the wooden studs but don't know if I should have a vapour barrier behind the backer boards. Also, one of the (external) walls will have the shower feeds, mixer etc. to avoid/minimise condensation is it ok that I fill studs with rock wool or should I use pipe sleeve insulation?

And again....thanks!

Carlos

 

[tictic]

your external walls are they solid or cavity...
solid yes use a vapour barrier

cavity no need to but you can if you want..

yes insulate..

pipes if your using copper then sleeve and insulate

if pushfit/speedfit ect no need for pipe sleeves.. insulate..

come back on when floors are lifted..


and just re-open this thread...dont start a new one..

 

[AdamCH]

Where would you put the vapour barrier?

 

[tictic]

if you have a...lets say 9inch solid wall[no cavity] and your studding it out and insulating between the treated timber.. studs/base plate/header plate

then you will want a vapour barrier so your isulation[rockwool]..ect doesnt get damp ect ..cold bridging...

so where do...you... think it will go...?


if you look through past posts i have gave advice on.. you will see the asnwer....and picture of moss/mushrooms growing out walls over toilet cistrens ect..cold walls/cold water..

seen few myself over the years in old properties