Self-leveller that can be drilled into?

[kjacko]

Hi all, so maybe not the usual question everyone asks….
I’m levelling my 6sqm en suite as it has a 10mm run off from one end to the other. It consists of bare floorboards that’s “mostly” covered in well screwed down 6mm ply. However where my 1400x800 shower tray will go, I’m removing the floorboards and installing 18mm ply. So there will be a 6mm difference in height between that and the rest of the room. The intention is then to apply the SA over the whole room to bring it all up to a good level. Min depth will be approx 3mm, max will be around 13mm.
Mapei ultraplan renovation has come recommended but I need to know that I can safely drill a 90mm hole for the shower waste through it and the 18mm ply beneath it without it crumbling.
Can anyone advise on an appropriate flexible self-leveller for my needs if you think ultraplan isn’t the best product. The other product that came recommended and that I’ve used before is pro-flex, but I’ve never tried to drill a big hole like what I need to do now.
Also (side question), can I use flexible tile adhesive to secure the shower tray, or best to go for the sand/cement mix?

TIA.

All advise appreciated.

Edit: i’ll be installing LVT onto the floor.

 

[Deleted member 174758]

Why not build up that 6mm difference with a layer of 6mm ply over the 18mm?

I have drilled through SLC in the past with a holesaw. Started by making a reverse direction cut for a few seconds before runnung in the "right" direction. Can be a little messy within a few millimetres of the hole, but otherwise seemed OK. Can't tell you what brand(s) it was, though

 

[jacko555]

Or cut the hole in the ply before the SLC, and get/make a cardboard cylinder to use as shuttering? The SLC will form around it, remove the cardboard and hole is there...

 

[kjacko]

Or cut the hole in the ply before the SLC, and get/make a cardboard cylinder to use as shuttering? The SLC will form around it, remove the cardboard and hole is there...

Lol, now why didn’t think of that?! Good idea

Why not build up that 6mm difference with a layer of 6mm ply over the 18mm?

I have drilled through SLC in the past with a holesaw. Started by making a reverse direction cut for a few seconds before runnung in the "right" direction. Can be a little messy within a few millimetres of the hole, but otherwise seemed OK. Can't tell you what brand(s) it was, though

But that won’t make good the unlevel floor. 10mm drop over 1.67m is quite a hill imo.
By levelling the entire floor I have a blank canvas that’s new and smooth enough for LVT.
I would think/hope that flexible and fibre reinforced SLC like the mapei ultra plan renovation (and similar) would take a hole being cored into it. Although I do also need to cut around for the first bit of 40mm coming off the trap.
So cutting the ply the. Shuttering may well be the solution here.

 

[foxhole]

If you intend to tile ply is too thin .

 

[kjacko]

If you intend to tile ply is too thin .

I did mention in my OP that I’m using LVT.

 

[foxhole]

I did mention in my OP that I’m using LVT.

Didn’t see the edit .