building a shower base - can i do this?

[dormermike]

Hi
I'm rebuilding my shower which leaked terribly after having it professionally done in 2018. This time, i'm doing it properly using backer boards (XPS) and tanking on top of those. Belt and braces. Its going onto a solid concrete floor so needs to be elevated.

Unfortunately, the mira flight shower tray riser kit I already bought can't be used (pipes etc), so i'm building a base. I spoke to Mira and they said to use minimum 22mm marine ply. I've got regular ply 18mm on hand. I'm wondering if i can double up the 18mm ply to make 36mm but if so, how would I fix the two pieces together?

Also is regular ply okay? Its got to be better than the chipboard the pro's used last time. I was thinking i could prime the edges with silicon or SBR (?) or something else.

Btw i also bought cement to bed the tray onto the ply but Mira are saying to use silicon.

thanks
mike

 

[Deluks]

Your ply will probably be ok, but a standard grade may delaminate if it gets wet.
Glue it together and use 30mm screws, you may want to give it a coat of something. Varnish or an oil based primer, at least on the bottom.
That said if your installation is spot on then it won't see a drop of water.

You could also use cement based tile backer board, two layers of 12mm glued together.

 

[Ivor Windybottom]

Don't deliberately botch the job, definitely don't use standard ply as it will fall apart as soon as it gets damp.

 

[dormermike]

Don't deliberately botch the job, definitely don't use standard ply as it will fall apart as soon as it gets damp.

Thanks, yeah, i'm trying to fix prior bodges so i definitely don't want to set it up to fail.

Where can I buy 25mm marine ply for a good price? I looked online and it was £90 for a sheet, and then £75 delivery! I looked in B&Q, nothing there, and same for selco.

 

[Ivor Windybottom]

Might it be called something else, e.g. exterior grade?

B&Q will also cut to size for free, so you should be able to get it cut into whatever size you need, plus car-sized offcuts.

 

[Deluks]

Tile backer is about £12-£15 a sheet

 

[noseall]

Its going onto a solid concrete floor so needs to be elevated.

Why?

 

[dormermike]

Why?

For the pipes and waste etc underneath it. Property is a 1930's bungalow, and the concrete floor is not insulated and unlikely to be particularly thick concrete so i'm not willing to run the waste in the floor with all that entails.

 

[dormermike]

Tile backer is about £12-£15 a sheet

Thanks. I understand you're saying i can use that instead of 22mm ply? I am not sure about that, but will look into it, thanks. Is certainly more readily available than WBP Ply, or at least cheaper

 

[noseall]

For the pipes and waste etc underneath it. Property is a 1930's bungalow, and the concrete floor is not insulated and unlikely to be particularly thick concrete so i'm not willing to run the waste in the floor with all that entails.

I think you'll regret that decision.

 

[dormermike]

I think you'll regret that decision.

Why?

For extra info Its a brick cubby of approx 830mm x 830mm x 2440mm and was a shower, raised, when we moved here in 2010. We then had it redone as part of a (very expensive) bathroom refurb in 2018 and it was left as raised then, so we're used to it. There are hot and cold feeds, electric underfloor heating and sensor wires, and a 40mm waste pipe routed underneath where the shower goes. So if i was to put it at floor level, not only would I have to channel the floor and SDS a new waste outlet, i'd have to re-route the cold and hot feeds which supply the sink units and cistern, and the wiring for the u/f heating.

 

[noseall]

Why?

Climbing in and out of a shower defies the convenience of having a shower. All of my customers want ever shallower access. Raising them up seems bonkers to me.

 

[dormermike]

Fair enough, but i'm replacing like for like in this instance.

In any case, this is bathroom number 3, so it is not the main bathroom. I'll be redoing the upstairs bathrooms myself (no chance i'm trusting anyone with that job after the mess and bodgefest downstairs) and i may put those at floor level as the joists align with the existing waste direction, so new solvent welded waste pipes under the floor, and the trays can be set onto cement on 22mm ply.

 

[dormermike]

Also the weird thing with this mira shower tray is that they are saying to silicon the tray to the plywood base, and silicon the wood blocks to the floor - basically silicon the crap out of everything. Every video i've seen has said not to silicon and to use either tile adhesive with a breakaway layer or a 5:1 sand cement mix to bed the shower tray. The tray looks excellent quality and has reinforcing ribs but i'm weary of just using silicon to bed it down. Equally wary of not following the manufacturer instructions!

 

[Ivor Windybottom]

Oh I missed that it was on concrete. In that case definitely don't put wood under, use sharp+building sand and cement, basically a mortar mix. Bed the tray directly onto it. Rock solid, it won't crack, rot or split the silicone seal to the wall ever. Just make sure your waste is accessible as otherwise the breaker drill will be the only means of access.

The above is what I did, but my base was already below floor level. I brought it up to floor level. Totally get why you want to keep the drain above the floor. Not pretty, but practical.