fixing shower tray

[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.