Thickness of base for a shower tray.

[amfisted]

Evening all

Following on from another thread where I asked about shower plumbing, I wanted to ask what constitutes a suitable plywood base for a shower tray when the ply will be sited on floorboards. I have 4 inch T and G boards on the bathroom floor, in reasonable condition and fairly level. I've bought 9mm ply for the shower tray base because 9mm brings the floor level up to roughly where it was before the previous floor tiles were removed. However, I've now noticed that in general, the advice given online is to use 18mm ply for a shower base. I didn't buy 18mm because I thought it best to keep the floor on one level, but on reflection it makes sense to have a more substantial shower base and use 9mm plywood as the base for the floorcovering across the rest of the room.

My question is this: as I've already bought two 8 x 4 sheets of 9mm, would it be feasible to use two sheets of 9mm ply, one on top of the other, to build up to the 18mm shower base, providing it was suitably waterproofed? Or am I better advised to buy a sheet of 18mm plywood?

 

[Wayners]

About 7 mins in covers your question.

Worth watching all though

 

[amfisted]

About 7 mins in covers your question.

Worth watching all though

Thanks very much. I don't intend to remove the floorboards and lay the plywood directly onto joists, but lay it on top of the floorboards because they're solid and in decent nick. It seems to me that would be the strongest base possible.

I'll get some 18mm ply on Monday. Hopefully they'll take back one of the sheets of 9mm in part exchange.

 

[drives]

Might be a bit late in the day if you have already bought the tray, and I'm not saying you don't want to firm up the sub floor as much as possible regardless of what your tray is constructed from- but the risk of cracking is the reason I went for a steel shower tray for the second shower room we did (with installation directly onto the subfloor). Now I wish I put one in the first shower room I did as well.

I'm sure a correctly installed stone resin tray will cause no bother etc. Just an option perhaps to consider and perhaps you would be able to keep the tray at the height you want.

 

[amfisted]

Might be a bit late in the day if you have already bought the tray, and I'm not saying you don't want to firm up the sub floor as much as possible regardless of what your tray is constructed from- but the risk of cracking is the reason I went for a steel shower tray for the second shower room we did (with installation directly onto the subfloor). Now I wish I put one in the first shower room I did as well.

I'm sure a correctly installed stone resin tray will cause no bother etc. Just an option perhaps to consider and perhaps you would be able to keep the tray at the height you want.

Tray is already bought and it’s not steel, but thanks anyhow for your thoughts and experience.

 

[Diver Fred]

18mm one piece WBP ply is a minimum. 22mm is better. Once the tray is bedded leave the 'bed' to cure for at 24 hours, better 48 hours before doing any thing on or close to it.
Once in place do not let anything heavier than a pencil drop on it - I know as the expletive deleted (assistant) dropped his tape onto the middle of a tray we just fitted the week before - a nice crack was the result so the replacement came out of his salary...

 

[dilalio]

Use some of the 9mm to make a cover for the tray once it's in!

 

[Madrab]

4 inch T and G boards on the bathroom floor,

Feck me - really? That's one thick floorboard!!

The trick with laying a tray down onto floorboards is ensuring there is enough support below it, either joists or dwangs underneath - ensure all the outside edges of where the tray will land has a joist or dwangs to ensure the flooring above won't deflect when weight is applied. As far as a board to sit on top, the board needs to be thick enough so it won't pick up any inconsistences in the floorboards, so the tray sit's totally flat to the board. That ensures there are no high or low points for the tray to flex on.

I wouldn't use anything less than an 18mm WBP or OSB.

 

[amfisted]

Feck me - really? That's one thick floorboard!!

The trick with laying a tray down onto floorboards is ensuring there is enough support below it, either joists or dwangs underneath - ensure all the outside edges of where the tray will land has a joist or dwangs to ensure the flooring above won't deflect when weight is applied. As far as a board to sit on top, the board needs to be thick enough so it won't pick up any inconsistences in the floorboards, so the tray sit's totally flat to the board. That ensures there are no high or low points for the tray to flex on.

I wouldn't use anything less than an 18mm WBP or OSB.

Thanks again. I'll put on my best "slightly dumb DIYer" smile, head for the builders' merchant and ask nicely if they'll change one of the 9mm boards for 18mm. Might ask if they can get some thinner floorboards for me whilst I'm there, hee hee.

 

[Madrab]

Don't forget to lift the current floor and make sure that the tray will be well supported edge to edge by joists or extra supports.

 

[dilalio]

I usually remove floor boards, brace the joists with noggins (dwangs as @Madrab calls them) and then use ply without the boards going back. This gives less height difference to make up between tray and rest of floor.

 

[amfisted]

I usually remove floor boards, brace the joists with noggins (dwangs as @Madrab calls them) and then use ply without the boards going back. This gives less height difference to make up between tray and rest of floor.

Fair comment, especially re the effect on height difference. The previous floorcovering was porcelain tiles on top of 5mm plywood, and following their removal there's a height difference of about 15 mm. I'll measure up once I get hold of that 18mm and consider my options. I used noggins on one previous occasion many years ago when I replaced an entire bathroom floor which had been destroyed by woodworm. I didn't use the right timber for the joists and just bought standard 5 x 3, but with no internet at the time to do quick research I eventually found out that I should have braced them with noggins to prevent twisting. I took up the boards and put noggins in herringbone-style, but despite that the floor always creaked like Hell.

 

[Madrab]

Yeah +1 with @dilalio - if you are looking for a floor level tray, tray height dependent, then that's what I did for my own en-suite tray. To allow it to end up level with the finished floor, (10mm tile with ditra matting, mesh UFH and a 4mm adhesive layer), the original P5 floor was cut out, dwangs installed and then 22mm OSB was installed and area was then fully tanked.

Ended up like this

 

[amfisted]

Yeah +1 with @dilalio - if you are looking for a floor level tray, tray height dependent, then that's what I did for my own en-suite tray. To allow it to end up level with the finished floor, (10mm tile with ditra matting, mesh UFH and a 4mm adhesive layer), the original P5 floor was cut out, dwangs installed and then 22mm OSB was installed and area was then fully tanked.

Ended up like this

View attachment 384965

And another thanks from me. My floorboards are 20mm thick, so 18mm would probably be perfect for our purposes, give or take the odd mm.

I've been having problems with the plumbing. I fitted 22mm/15mm reducing compression tees for the rising shower feeds, and one of the tees leaked constantly until I'd tightened it up so much that the olive was crushed. So I binned that, cut the pipe back to a point where I could take up floorboards to improve access, added a 22mm/ 15mm straight connector and that leaked as well. So I bought solder ring reducers and found to my dismay that the big end wouldn't fit over the end of the larger pipe. I began to wonder whether this was actually 25mm pipe, but the reducer wouldn't fit over the new 22mm either. Are you meant to heat them up so that they slide over the pipe? Anyhow, I refitted the inline compression reducer and so far its stayed dry. Good thing I'm not on a deadline for this job.

 

[endecotp]

So I bought solder ring reducers and found to my dismay that the big end wouldn't fit over the end of the larger pipe. I began to wonder whether this was actually 25mm pipe, but the reducer wouldn't fit over the new 22mm either. Are you meant to heat them up so that they slide over the pipe?

No.

Is the pipe squashed into an oval?