Shower tray onto chipboard - what to do

[markyyyyyy]

Just installed new 22mm chipboard and part of me is saying to put down ply so I don't regret it in the future (just for shower area).

Can I get away with bedding the shower tray straight onto 22mm chipboard. If so, what do I seal the floor with first?

If I go down the ply route, is 12mm ply screwed ON TOP OF chipboard ok, or do I need to remove the chipboard and screw down 18mm?

Cheers

 

[johnny2007]

If the height is still ok, 12mm marine ply would be ok.
I have seen many installers fix the shower tray on the green chipboard flooring.
They tank it first with the same tanking kit they use for the walls.
If you think about it, a good installation with a bead of silicone on the edges of the tray against the wall, plus tiles, finishing silicone or trim, makes the chipboard quite unlikely to get wet, unless something goes wrong.
In that case plywood will only last longer, but eventually will give in.
I have lifted shower trays installed 20 years ago and underneath was as dry as a bone.
Then of course sometimes you find everything rotting.
99% of the times it happens when silicone between tray and tiles has failed and not replaced.
Maintenance is essential.

 

[Deleted member 174758]

Would 12mm cement board such as Hardibacker not be better than 12mm plywood? (Over the sub floor, that is) After all, plywood can rot if it gets wet - cement board can"t. I can see that the same advice about joints needing to be sealed well applies, though

 

[markyyyyyy]

I've cut out a section for 18mm who plywood for peace of mind. This will finish 4mm below chipboard floor level but with mortar bed will be higher