Shower tray on suspended floor

[russbif]

Hello, first post, I know this has been covered in previous posts but I have a slightly different question, the house I am installing the shower in is an early 60's bunbgalow, the floor boards that the shower tray will be mounted on are thick and seem rock solid, not the modern thin jobs, do I reallly need to remove them and replace with marine ply, can I not just cement on top of them and bed the tray in, or, would it be better to screw the ply ontop of the floor boards? surely that would be even stronger.
Opinions and advice please

 

[Burnerman]

No need to remove the old boards at all....place plywood on the top of them if you need to.
One good move would be to leave some boards loose on one side of the tray, just to see that the drainage is sound once the shower is commissioned.
John

 

[russbif]

I plan to have a removable board in line with the waste pipe, screwed down of course, so that i can always access the waste if necessary, thats if I go with sanded boards rather than tiles on the floor...

If i do as you suggest, could I get away with a thinner board, don't want the plinth to be too high

 

[Burnerman]

My own property has good quality floorboards, nice and flat, thick and in good condition.
For my shower tray (1200 x 600 stone resin) I bedded it down on a thick layer of silicone to give it a cushion, and that was 10 years ago. Absolutely no problems with it at all and I did check for level first!
I don't go for trays with legs though as they can't be as stable as those without.
Thinner ply sounds fine for you - you just need to avoid any rocking of the tray.
John

 

[russbif]

my tray is 1200 x 900, I am very confident of the floorboards, what sort of silicone did you use? my only fear is that the base of the tray would not be perfectly flat and flex over time

 

[Burnerman]

I used the B&Q trade pack silicone (smells of vinegar).
Try your tray as a dry fit, and see if there's any rock.
John

 

[russbif]

Once I get the bath out I shall check how true the floor is, then, if its level get some 5mm marine ply, (if they make it) and probably put a cement bed on that, silicon is fine but it still flexes