Shower tanking advice

[Night Owl]

Hi, I'm looking for some advice on the best practice to prepare my new shower area for tiling.  It's situated in a first floor room that I have created in my loft space.  The marine plywood floor is sat on 8x2 joists and is solid.  The floor covering will be done in Luxury Vinyl flooring which claims to be 100% waterproof.  Shower area will be tiled and a glass screen fitted.  The cut out in the wall will have a metal preformed niche installed.  Finally, the shower itself is a hansgrohe bar type, no rain shower head though.  I have boarded out the stud walls with Marmox Multi board and sealed all of the joints with Marmox MSP360 adhesive/sealant.  Fixing screws and washers have been covered in Marmox waterproof tape.  The remaining walls have been skimmed and decorated.

 

I'm now at the stage where I want to add some tanking material prior to installing the shower tray (Mira Flight 25 Low Level 1200x900).  Planning to use something like CT1 for bedding the tray onto the floor.  I have a Dukkaboard Aqua 77 5kg tanking kit ready to go and am looking for the best way to go about this.

 

 

I've been thinking about the various ways to go about this but am undecided on which method would work best.

 

1. Should you lay the vinyl flooring first then place shower tray down on top of it or should the tray go straight onto the plywood?  I'm guessing the answer will be no, but my thinking is it will at least provide another layer of waterproofing.

2. Should the plywood be tanked using the kit before fitting the tray?  Thinking about using the fabric along the wall/floor joint and up the corner join with a good covering of the tanking material.  Also thinking of coating the plywood with it where the tray will sit.  I then ask myself the question that if water reached the tanked plywood, where is it going to go then so probably a waste of time!

3. Bed tray onto plywood with CT1 and along the back of the tray where it will join the wall board - will try to create an upstand with the CT1 as I've seen mentioned here.  Then use the tanking kit to make the join between walls and tray plus up the corner joint approx 1.8m.  I have also got a good bit of the waterproof tape left which could do this job if considered just as good?

 

The walls will then be tiled with 600x300 porcelain wall tiles.  Will probably get a professional in for this but wondered if it's worth requesting him to use the resin type grouts I've been reading about?

 

  

 

I realise there will be more than one way to go about this but am looking for advice from those who have done this type of job before.

 

Thanks.

[Beau]

 

 

Just done a couple of new showers in our place. I put the tray on the ply with no tanking, because as you say, water really shouldn't be getting to it anyway. Also, I didn’t want the flooring in while I'm still bashing around with shower panels, toilet pans, etc.

Fixed the tray down with OB1, which is much like CT1, and used some levelling packers as the floor was not quite perfect. I had a Mapei tanking kit but had problems, as the tape wouldn't stick to the shower tray — remedied it with more CT1. I had enough tanking to cover the whole area, not just the joins, so I did the whole area anyway.

 

Having used these tanking kits in our old place nearly 20 years ago and never having a leak, I trust them.

[Nickfromwales]

Absolutely do not lay the tray over LVT!

 

You need to primer the plywood and bond the tray down, usually done with flexible tile adhesive but you can check with the MI’s to see what they suggest. 
 

One key thing is to decontaminate the underside of the tray, as sometimes these have things like release agent etc or just a lot of dust from being refinished, and then nothing will stick to it.

 

Set the tray in to the return walls with CT1 / similar and NOT silicone. 
 

Search in here for tanking / wet room / shower tray etc and you’ll see many of my ramblings on how to best achieve this. 
 

NEVER use a kit or other that has something that sticks to the tray, these are not a good product / idea imho, as you’re forever reliant on that adhesion. 

[Night Owl]

Thanks Beau/Nick for your replies today,

Some good info in there for me to refer to, especially priming the plywood - completely slipped my mind.  Thanks also for confirming not to lay the tray on top of the LVT.  I'm not going to be able to do this job now until towards the end of next week as after inspecting the tray today I've noticed it is delaminating slightly in one corner, only a small amount but not worth the risk.  Annoying as this is the second tray I've had, first one was warped.

 

Manufacturer (Mira) says to bed the tray on a 5/1 sand cement mix or silicone.  I'll go for OB1 to bed it down and CT1 to seal it to the walls.

 

Nick, could I just confirm with you when you say to set the tray into the return wall with CT1, do you mean to cut a channel into the wall then push the tray into the recess made after packing it out with CT1?  If you do mean this, how deep should the recess be and apologies if I'm being a bit thick here but which is the return wall - the 1200 or the 900 length of my tray? 

 

Thanks again for the replies.

[Night Owl]

Reading my reply from Nick again I now realise he was referring to both walls for letting the tray into.

Im probably over thinking this but at the moment I have the multi board which is 100% waterproof installed from ceiling to the plywood floor where it is sealed.  If I cut into the board to let the tray in I will be losing the waterproof seal that is currently there. The walls are of stud construction so will then be open where the cutout is made for the tray. 

How do I then form a good barrier with CT1 within the cutout?  The boards are 12mm thick and insulated with a foam type material, xps?  Partially cutting into the board wouldn't be easy due to the insulation with respect to getting a neat cutout.

[Nickfromwales]

10 hours ago, Night Owl said:

Reading my reply from Nick again I now realise he was referring to both walls for letting the tray into.

Im probably over thinking this but at the moment I have the multi board which is 100% waterproof installed from ceiling to the plywood floor where it is sealed.  If I cut into the board to let the tray in I will be losing the waterproof seal that is currently there. The walls are of stud construction so will then be open where the cutout is made for the tray. 

How do I then form a good barrier with CT1 within the cutout?  The boards are 12mm thick and insulated with a foam type material, xps?  Partially cutting into the board wouldn't be easy due to the insulation with respect to getting a neat cutout.

Zero cutting of anything! 

 

Whoa! 
 

I am referring to setting the tray on the deck, with the CT / OB 1 under it, and then you pull the tray away from each wall of multi board by about 5mm, and then pump the gap full of CT1. 
 

You then push the tray back to the wall, displacing the excess CT1 and wipe the excess away (baby wipes, lots of them, are your friend here).

 

Check for level, and leave to cure for 48hrs. 

[Night Owl]

Thanks again Nick, that's perfect.  Crystal clear now!

 

Will hopefully be able to get onto this job now at the weekend once the new tray has arrived.  

[Nickfromwales]

13 hours ago, Night Owl said:

Thanks again Nick, that's perfect.  Crystal clear now!

 

Will hopefully be able to get onto this job now at the weekend once the new tray has arrived.  

Everbuild do a version of CT1 called “crystal clear” lol.

 

We’re on the same page   

[Super_Paulie]

Is OB1 just CT1 then, it's cheaper but I've never heard of anyone using it.

[andyscotland]

9 hours ago, Super_Paulie said:

Is OB1 just CT1 then, it's cheaper but I've never heard of anyone using it.

 

I may be wrong, but I *think* it's essentially the same product, made by staff who originally worked on CT1 and then split off to do their own thing after the company was sold or something like that.

 

I've used it quite a bit and it's worked well.

Edited Wednesday at 08:24 by andyscotland