Stone shower tray - again

[Keefiedee]

I posted a week ago feeling very daunted by the instructions for fitting a stone shower tray and questioning the need for bedding it into mortar. Thanks to all for the very helpful replies.

I have now built my frame and cut the 18 mm ply to shape. What concerns me now is how thick does the mortar needs to be? My problem is that there is very little space between the top of the compression fitting on the shower waste, and the bottom of the ply. I guess I can chisel out some of the ply to give greater clearance, but it would be helpful for me to have an idea of how thick the mortar should be. I guess not very thick as I did find flexible floor tile adhesive recommended as an alternative. Any thoughts?

Keith

[Keefiedee]

I posted a week ago feeling very daunted by the instructions for fitting a stone shower tray and questioning the need for bedding it into mortar. Thanks to all for the very helpful replies.

I have now built my frame and cut the 18 mm ply to shape. What concerns me now is how thick does the mortar needs to be? My problem is that there is very little space between the top of the compression fitting on the shower waste, and the bottom of the ply. I guess I can chisel out some of the ply to give greater clearance, but it would be helpful for me to have an idea of how thick the mortar should be. I guess not very thick as I did find flexible floor tile adhesive recommended as an alternative. Any thoughts?

Keith

[Skipweasel]

At its thinnest - non-existant. If the very lowest part of the tray is just kissing the substrate through the bed of cement it won't matter - what matters is that those bits of the tray that wouldn't otherwise be fully supported are - by the mortar.

[John Rumm]

That's probably why they normally suggest 1/2" ply ;-)

Having said that, I have done it on 19mm myself before. To make fitting the waste easier, I routed out an area around the waste on the underside

- in effect reducing the board thickness to 12mm at that point. Then bedded it on about 1/2" of mortar.

(I laid the bed, shoved a couple of scrap offsets of 15mm plastic pipe over the mortar and pushed it in so that it was in contact with the board. Dropped the shower tray onto the pipes (a couple of mm clear of the screed) and lined it all up, then pulled out the pipes to drop it into place)

[Keefiedee]

The recommendation for 18 mm ply came from this very newsgroup in reply to my previous post! Certainly I feel happier with 18 mm as it seems much more rigid than 12 mm 9 (although I suppose that doesn't really matter once it's on the framework.

Thanks for the suggestion about the 15 mm pipe though. I was a bit concerned about trying to lay a rather heavy shower tray on a bed of mortar right up against two walls and having to jiggle it to make sure it was properly bedded. Which brings me to another question - I get the feeling it might be best to go for a fairly moist mortar mix - am I right, and if so, how moist?

Keith

[John Rumm]

Indeed, I went with 18mm for the same reasons you did. However the instructions on mine suggested 12mm ply.

As you would for bricklaying really. It will be a bit more workable than with high suction materials like bricks anyway. You can add plasticiser to increase workability in place of extra water.

Once the tray is down, stick a level across it and tap it down until level in both axis.