Large stone resin shower tray bedding onto Plywood overboard on floorboards - Tile Adhesive or Cement.

[axt]

Hello,

I am sure this has been discussed before but I have yet to find a certain avenue on this as there is a lot of conflicting information.

Essentually I have a room which will be simple Vinyl flooring (fully tiled walls which are now all jackoboarded ready). I have a 1700x800 stone resin tray waiting to go in, which will be hard as the room is 1750 wide and hence will have to be carefully lowered into the alcove onto the mix.

The floor is 22mm T&G boards (and some 22mm chipboard to fill in gaps. I have overboarded it all with 5.5mm Class 3 ply (and it was beltsanded and made level before). Screwed on 150mm field all round. Its fairly good, flat and solid.

The tray (as per all stone resin trays it seems) suggests bedding on a sand / cement base. Lots of people have suggested to me to use Slow Set Flexible Tile adhesive, which I like the idea of a little more as it is essentually a giant tile. However I am going round in circles as I am not familiar with tile adhesive on the priming front. Should I PVA the ply, or use something like Evo-Stik Flexibond Primer - they make little mention of Plywood in the datasheet.

I dont really want to put down aquapanel or Hardi on the floor as it would raise the tray up and give me an awkward edge, the ply is perfect for the Vinyl.

My current plan is just Primer & Adhesive - but I am not certain on which primer (SBR / PVA / Evo-Stik etc) and/or which adhesive (or even if Sand / Cement is indeed better on a ply / wooden floor?).

Any advice gratefully received!

 

[Diver Fred]

I would have laid 22 or 25mm ply (and in fact still would) as a base. Then I'd use a stiff mortar mix (4 soft sand/1 cement) to bed the tray on making sure the tray is level in both directions, leave it at least a week before putting any weight on it.

 

[simplesteve]

SBR for me, mixed 3:1. Leave overnight to dry. BAL Rapidest tile adhesive.
Has worked well for me over the years.

 

[axt]

The thing about laying additional ply down is that it kind of negates the point in manufactourers making these low profile trays. I mean, why buy a 25mm low profile shower tray if you are then going to stick that same thickness underneith it? (mine is actually 45mm I believe, but still). Unless you overboard the entire floor with 18 or 22mm ply then its going to be hard to dress up the flooring / tray interface.

I have already overboarded with 5.5mm good quality ply as that was what the floor laying folk kept suggesting was vital for Vinyl, now I am on shower tray duty it seems its all about the 18 and 22mm ply... My floorboards themselves are 22mm which is better than the 18mm that seems more common, and the joists near (most) of the tray are fairly close to a supporting wall so it is all fairly firm so I am hoping to just leave the floor as it is.

I have been reading up on S1 and S2 tile adhesives. It would seem the ideal thing would be a slow set S2 adhesive like Rocatex C2TE S2. Has anyone had any experiance on using this sort of (S2) adhesive in this application - it seems ideal?

C2TE S2 Ultimate Slow Flex White - ROCATEX

www.rocatex.com

 

[foxhole]

Cement board is more stable than any timber. Sand cement mix works well but may need a thicker bed than tile cement .

 

[axt]

How feasible is it to use this S2 Tile Adhesive - bearing in mind it is standard, not slow, set but is very flexible, so hopefully mitigating some of the potential issues of being a timber floor:

UltraTile ProFlex S2 - Fibre Reinforced Flexible Tile Adhesive 20kg - Ultra Products

UltraTile ProFlex S2 – Fibre Reinforced Flexible Tile Adhesive 20kg UltraTile ProFlex S2 is a single part, rapid setting, flexible, fibre reinforced adhesive for wall and floor tiles. It is specially formulated with FibreBond technology, enhanced adhesion and flexibility, making it ideal for...

www.ultraproducts.co.uk

Looks like I would have about 20 mins to get the tray down into position once screeding it out? Would likely need to have the tray hanging on a crane over my head ready to go, or be very prepared I guess?

Many Thanks.

 

[simplesteve]

Yip, you need to be prepared !
I also see you’ve changed from slow set to rapid set, which is what I’ve always used ( albeit I prefer the BAL flexi rapid )
Top Tip :- put the tray face down, flat, on a carpet and unwrap it. Then take a known flat edge ( 1200 or 1800 spirit level usually ) across the back of it; fronts, sides,diagonals:- you’ll be amazed to how “ un flat” your tray is on the back, so you’ll now know where the Voids/Highspots are BEFORE you put it down

 

[cdbe]

Slow set flexible with SBR primer works for me. Rapid Set is for tradesmen who do it in a day. Never understand why they sell so much in the DIY sheds without flagging it up - I just picture diyers mixing a bag full then having a cuppa and a bit of lunch before getting started.

 

[simplesteve]

As a tradesman, I agree with @cdbe above, and TBH 95% of the time we all use slow set to tile the bathroom walls.
However, in the case above, we are talking an area of less than 2m2, hardly a full bag or a large area! And trust me, the O.P. will be focused on getting that tray down, absolutely no chance of mixing a batch then lunch

 

[asnoop20]

I redid mine recently after a reputable plumber ****ed it up.

Mine was put on 22mm marine ply but nothing stopping you putting wood in-between the joists so long as you support it well enough to ensure it doesn't move at all. In my case I wasn't after a sunken or flush tray install.

The previous tray used tile adhesive, unsure if it was flexible. The tray cracked but it may not have been down to this as there were a number of installation faults. When I redid it myself I used a weak mortar mix. The tray should effectively float on top with silicone at the sides to allow for wall movement. I really don't think it matters as tile adhesive and mortar should not be able to chemically bond to the resin bottom. Really it's only purpose is a leveller and to angle it a little for run-off in direction of the drain hole (which depending on tray can be in the center or any of the corners. I found getting the levelling correct was a pita and the biggest issue.

What I do think is critical is the design of the tray. Flip it over and the base should be entirely flush. My first tray had large voids where the sides had been formed and either they weren't filled as a cost cutting measure or it was just ****. It allows the bed mortar to fill it and prevents the tray from moving.