fixing shower tray

[mitchino]

I seem to find a lot of different opinions on fixing walk-in shower trays to floors. I will be fixing to a marine ply base screwed into joists with noggins. The manufacturer says bed into a weak mortar mix, but I read that this can lead to problems when the mortar dries out. Some say silicon, some say low expansion foam, some say tile adhesive, some say mortar.

What is the definitive way to fix a shower tray?

 

[IND_Nick]

I think you will always get a few different opinions on the best method. However we always use tile adhesive and have never had an issue or call back over a failed tray.
As you stated make sure it is on one piece of ply, if necessary overlap the ply to make sure it is solid. Prime the wood the night before and then set on 5mm to 10mm adhesive bed. 24hrs later it should should good to go.
One of the biggest problems we find is that everyone is going for large trays and they are rarely flat and true. Always make sure the edges that the enclosure sits on are level and you should be fine.

 

[ShaunCorbs]

Is the tray fully level on the bottom or is there a few indents etc ?

 

[Knappers]

Mortar mix or tile adhesive (mortar based) wouldn't recommend anything that's too sticky or has any flex incase it moves or ever has to come out.
I wouldn't be happy trying to strip out a tray stuck with silicone or contact adhesive!

 

[mitchino]

It's one of those trays with lots of moulded parts underneath. The edges and a kind of wheel pattern would touch the ply and then the moulded bits are recessed up to maybe 20mm. The kind of thing you see at the end of this video:

MX Group -The Leading Manufacturer of Showers, Shower Trays and Shower Accessories

 

[EvilDrPorkChop]

I always expanding foam them. Not everyone agrees, but never been called back to one or had any issues over the years.

It's great as it fills in all the hollows underneath the tray, and they grab like ****. They're solid after it's gone off.

 

[ShaunCorbs]

Sand a cement required then as it will fill in all the gaps

I know if you use the leg kits they normally only span normally a 4” circle but manufacturers say that’s fine somehow but when it’s beaded down it needs full coverage

 

[Harvest Fields]

What ever the manufacturers instructions say. If there is any issues with the tray it will come back to you.

 

[king of pipes]

I always use a good quality flexible tile adhesive as others have mentioned prime well with SBR before bedding down never had a issue doing it this way . Kop

 

[mitchino]

Thanks all, I think I'll use mortar to comply with the guarantee. I like the idea of the low expansion foam though, I've heard you should 'decouple' the shower tray by squirting the foam down, then laying a thin polythene sheet over the foam, then the shower tray on top. That way it's not a nightmare to replace if something does go wrong.

 

[king of pipes]

New one on me that method surley theres nothing fixing it down then if the foam is under a polythene sheet ? please post a few pictures interested to see how this turns out. Kop

 

[EvilDrPorkChop]

New one on me that method surley theres nothing fixing it down then if the foam is under a polythene sheet ? please post a few pictures interested to see how this turns out. Kop

Yeah I don't see how it would work either..

 

[Knappers]

I did a shower once, did a proper job, boarded and everything, set on screed, backer boards etc.
The bottom row of tiles kept cracking at grout line. After several return visits we concluded that as the fella was built like Thor and well over 20st it was the joists flexing?
Not sure what I'd have done about that but it wouldn't have been to set it in foam!
Eventually customer moved and I heard no more about it

 

[mitchino]

So I finally installed the shower tray on a bed of 5:1 mortar. Levelled it then weighed it down with 200kg of weight, and left for 24 hours. Upon inspection next day, the base of the shower tray is rock solid, but I can still see a mm or two of flexing at the edges. Extremely annoying but is this anything to worry about?

 

[king of pipes]

If it can flex then it can crack!! you will have to make the decision is it worth taking the risk . Kop

 

[EvilDrPorkChop]

So I finally installed the shower tray on a bed of 5:1 mortar. Levelled it then weighed it down with 200kg of weight, and left for 24 hours. Upon inspection next day, the base of the shower tray is rock solid, but I can still see a mm or two of flexing at the edges. Extremely annoying but is this anything to worry about?

Should of foamed it

 

[WC1]

The undulations on the underside are what would then grab the tray and stop side to side movement. Some say to do this with tile addy to decouple the tray from floor movement.
Also 200kg of weight.? Where from?

 

[mitchino]

The 200kg was made up of 20 x 10kg stage weights.

 

[Harvest Fields]

The 200kg was made up of 20 x 10kg stage weights.

Was this weight just in the middle of the tray or distributed evenly?

 

[mitchino]

They were distributed around the edges.

 

[IND_Nick]

200kg is a bit excessive, good chance that the weight actually bowed the tray as it set unfortunately and once removed it is just will just spring back.
Never seen people weigh trays down as they are normally heavy enough to start with.
As said above if there is any movement on the tray it is likely to crack or break the seal with the tiles/wall etc.
Are you able to wedge the edges down in the wall to stop the movement. Unless it is completely solid I wouldn't continue with the installation unfortunately.

 

[mitchino]

I think for sure what's happened is, by putting the weight around the edges, I've bowed the tray a tiny bit while the mortar set. Once I took the weight off, it left a bit of spring at the edges.

All stripped now and ready to try again. I contacted the tray manufacturer and they say I can use tile adhesive as long as it contains portland cement. I assume Mapei flexible adhesive does, that's what I'm about to use.

They also say don't weight the tray, just settle it in.

Fingers crossed I get it right this time!

 

[mitchino]

So I have now bedded the tray using flexible tile adhesive. Probably used way too much on the advice of another plumber and the tray is now sitting on a good 10mm of adhesive above the plywood base. It's level though and I can use a bit of quadrant to hide the gap once the flooring is in.

 

[ShaunCorbs]

10mm notched trowel normally

ends up around 4-5mm bed

 

[Harvest Fields]

Had a tray once that I set twice with a 10mm and there was movement both times. Set it on 18mm shrank down to about 10mm once level (sorted) but looked a little odd. Couldn’t notice once siliconed the edge though.