Shower tray on chipboard

Discussion in 'Carpenters' Talk' started by steven123, Nov 7, 2021.

  1. steven123

    steven123 New Member

    Partly out of ignorance i installed green chipboard where the shower tray will go.

    I installed a lot of noggins so there is virtually no deflection in the floor (joists are also at 400mm centres and the span of the joists are only 1.5m). I was getting ready to lay a bed of sand and cement on the floor when i discovered chipboard is really not best practise (i felt like a bit of a war criminal when reading forums online). The floor is limited head height, so overboarding isn't a preferred option. I think my 2 current options are:
    a) Paint the chipboard with black bitumen paint (blackjack) so it doesn't absorb any moisture from the mortar mix (absorbing water could mean the mortar sets weaker / cause chipboard to swell) and then press on with putting down the tray
    b) Rip up the chipboard and replace with 18mm marine ply (for piece of mind this wins out but quite a lot of work involved at this later stage, logistics and cost)

    Appreciate any thoughts and inputs.

    Thanks,

    Steve
     
  2. Jord86

    Jord86 Screwfix Select

    Be careful what you read on forums, you can have the local ice cream man advising you on how to wire your house :confused: Leave it down, it's fine, though I'd opt for bagged tile adhesive rather than sand and cement (I know shower tray manufacturers stipulate mortar) but that's just my preference and you normally have some on site in preparation by then.
     
  3. woodbutcherbower

    woodbutcherbower Well-Known Member

    100% agree with Jord on this. Use a decent quality cement-based rapid set adhesive such as this one and you’re good to go. Mix it up a little thicker than normal, otherwise it will spread too far when the weight of the tray hits it;

    https://www.screwfix.com/p/mapei-rapid-set-wall-floor-adhesive-grey-20kg/29634

    Probably a good idea to prime the chipboard with SBR first.

    So - Cornetto, anyone ?
     
    steven123 likes this.
  4. CGN

    CGN Screwfix Select

    As above, as above.
     
    steven123 likes this.
  5. pppmacca43

    pppmacca43 Super Member

    I’ve recently put mine on 22mm T&G green chipboard, it was a Mira flight tray and Manufacturers instructions stated you could stick down with silicone or cement, so I did it using plenty of CT1 sealant and adhesive. My floor was dead level so luckily didn’t need to worry about levelling the tray on a bed of mortar. I also siliconed the sides to the walls before putting a thin bead around the top edges, I then tiled over and siliconed the Join between the tiles and the tray with Dow Corning silicone. It’s also sealed around the bottom edges where it meets the floor.
    Not sure if this is an option for you, as u will want to follow manufacturers instructions, but it’s solid as anything and works well.
     
    steven123 and CGN like this.
  6. steven123

    steven123 New Member

    Thank you very much for the responses! I'll crack on with laying the tray on the chipboard. I've used an extremely thin coat of black jack paint on it so it wont absorb the moisture from the cement mix during the bedding in.

    Due to a very slight level issue I'm going to stick with sand and cement. Its going to be set in an alcove area, with shower panels going over the top (not tiles) and its a stone resin tray so should be very low chance of lifting being an issue - i just need a good bed to support it evenly.
     
    pppmacca43 likes this.
  7. Wayners

    Wayners Screwfix Select

  8. steven123

    steven123 New Member

    Thanks Wagners. I did watch this start to finish which was one of the reasons I considered changing out the chipboard. I satisfied myself it was sturdy enough with all the noggins and screws to proceed with the chipboard though. The shower tray is now bedded in on sand and cement, appears to be rock solid.

    FYI: the last stone resin shower tray that was in place (I didn’t install) lasted 20 years on normal chipboard, with no noggins and wasn’t bedded in or stuck down (no silicon, tile adhesive or sand/cement). I may have got lucky…
     
    Wayners likes this.
  9. Wayners

    Wayners Screwfix Select

    Think you will be fine then. Sounds like it's all well fixed in
     
    steven123 likes this.

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