Installing shower tray- advice wanted please

[stefj]

I'm about to install a shower tray in a corner of my bathroom and would welcome any tips and answers to a couple of questions.

I'm replacing some uneven floorboards with 22mm P5 chipboard flooring and I'm going to buy a Mira Flight tray 1000mm x 800mm and a bifold door with side panel.

The tray's waste hole is in the middle of the short edge.
I have some 12mm marine plywood sheet.

My questions-

1 Is there any advantage in screwing the marine plywood onto the chipboard flooring and then fixing the tray on top of the plywood?

2 Whats the best stuff to seal the chipboard or plywood?

3 Miras instructions say to use silicone or sand/cement to bed down the tray. I'd rather use silicone but don't know which one is best. There are plenty to choose from at various prices. Can anyone recommend a suitable brand/type of silicone to use?

Any tips or other help would be very much appreciated.

 

[Burnerman]

Just a few points to mull over before you get stuck in....
It's a great idea to have the shower drain accessible to check for leaks etc.....it wouldn't be the first time that an adjacent floor has to be lifted or even a ceiling dropped for repair
It may be possible to place the tray on a 4"x 2" timber plinth to get this, or get the fall of the drain.
Either way, its a good move to replace uneven boards with P5 chipboard and you can use your marine ply too, screwed down.....either way, the tray must be level in both planes and have no rock. The drainage slope is incorporated within the tray, and you need good levels for tiles or whatever.
The tray is fine bedded down with a thick, even layer of silicone - I use B&Q's general Soudal silicone for this. Silicone takes up any fractional rock of the tray and keeps things stuck down.
By all means seal the timber with a waterproofing solution if you wish.
John

 

[foxhole]

Fit a top access waste so no plinth required.

 

[stefj]

Thanks both.

The Mira tray I intend buying is about 40mm high and the waste fitting is supplied with the tray, so I hope it will be accessible.

I've got some Jewson PVA. Would this be okay (diluted) to seal the plywood before laying the shower tray on top?

I can't find Soudal silicone on the B & Q website and the nearest B &Q is quite a way from me. There is a Screwfix branch much nearer. Can anyone suggest a suitable silicone from Screwfix?

Thanks again

Stef

 

[Burnerman]

Your pva idea is just fine, silicone wise this is fine for the tray cushion:
https://www.screwfix.com/p/no-nonsense-general-purpose-silicone-clear-310ml/35887
Dow Corning white silicone is probably the best there is for other uses such as around basins etc.
John

 

[stefj]

Thanks John,

I've done a bit of searching on the web and a lot of professionals seem to favour a sand/cement bedding. Is this more/less reliable than silicone and easier or harder to do.

A daft question: What type of sand - Building sand (bricklayers) or concreting sand?

Thanks
Stef

 

[lostinthelight]

https://www.wallsandfloors.co.uk/blog/can-i-use-pva-prime-surface-tiling/

 

[Burnerman]

Shower trays - irrespective of the type but the stone resin ones are the best - need a nice, flat base for them to sit on. They do not like uneven or sloping surfaces and certainly there must be no projections to create a pressure point.
A sand and cement bed (builders sand, stiff mix) may be fine to create a good surface on concrete or tiled surfaces, but in your situation a silicone bed is fine - I don't like the idea of cement on top of timber!
Anyway, these are just my opinions and others may differ.
I think the Mira Flight is an excellent shower base - I have four and all have been really good quality for the price. I don't like the bases being raised on legs but I have built a timber base to get the drain levels correct.
There's no actual need to pva the timber below (incorrect stuff to tile onto, incidentally so bear that one in mind).
Have you considered MultiPanel as a shower wall medium?
John

 

[stefj]

Thanks everyone.

The info on the web link from lostinthelight is very interesting.

I've decided I'm going to go for the silicone solution without using PVA with 12mm plywood on top of the new P5 chipboard flooring.
I'll be laying the floorboarding and ordering the Mira tray next week.

Thanks again all.