Onoff

I'd just man up! ? No mates local who'd help for a barbie and some beers?

Can we maybe see the bit of the plan where it's "clear"? If it's labelled I imagine it's clear cut in your favour but if down to fine detail, then a 3rd party (judge etc) might say it's 50/50.

So if the finishes on the wall in question are shown, clearly in plan and the builder hasn't read them imo it's down to them. Doesn't matter how you've provided it if they've missed it.

Instant man cave. Love it!

When I do fabrication drawings I'll do the standard top, side and end 3 views but will often provide a 3D view(s) too. Tbh I'll often JUST dimension a 3D view. I generally draw just small, bespoke brackets mind. A picture says a thousand etc. I'll even give the fabricator a flash looking render of the item. I think the best way is to admit to the builder you understand the fault doesn't lie with him (don't admit it's your fault). It'll build bridges. I'd let the architect know you're not happy though. Ask is there some way the elevation could maybe be temporarily clad or sheeted with a view to doing the cladding later. Does the cladding get stuck onto blockwork or mesh etc?

Not the contractors fault imo.

If you end up digging your floor up you might consider digging a bit deeper then building it back up with a good layer of insulation (like 160mm) and maybe even some UFH pipes?

I don't think your tank will be properly waterproof if you do the base and walls separate. On big sites I see they do the concrete structure then fit purpose made liners when doing things like sprinkler tanks. Liner needs periodic replacement. To do it your way, even with waterproof concrete I think you need to be incorporating waterbars. For example: https://www.arconsupplies.co.uk/waterproofing/swellable-waterbars You could do it in one hit with a big shuttered and braced box inside a box then pumped concrete.

I'd use Spax flooring screws. I'd do nothing until I knew where pipes and cables were.

5:1 pva the area, whilst still tacky get the bonding in there in a couple of layers. Leave a few mm under then multifinish.

I'm confused...I'd heard of this as i said but never read up on it until now. Depending on what you read the red ash was used UNDER "normal" concrete as a hardcore/filler. I took it that it was mixed in with the concrete. Tbh I reckon both scenarios might have happened. Your photos look like red floor paint at first glance.....is it red all the way through?

Red ash from blast furnace slag. Wife's uncle & cousin are builders up in Stoke and he's mentioned it. More common in areas that historically had such works. Some reaction happens when it gets wet even years on. As an aside I believe German engineers used similar ash in constructing the Channel Island defences (again because of shortages). Found it made really strong concrete. Says something that they're still up and in such good nick!

What grids can I ask please?

Then you can build a shed with them!

+1

A GD build at Lammas use recycled EPS beads as floor insulation I seem to remember. Justified on the basis it would otherwise have gone to landfill. All they had to do was collect. They also used rammed earth tyre walls, again gotten free.

Whoops...maybe...I'll have to check!

If you want to do a super neat job... Silicone only the back of the channel where it goes on the wall as described above. Don't run a bead up the outside unless needed for cosmetic reasons. Use a Fugi kit to do any beads. All the rest are poor imitations: https://www.amazon.co.uk/Cramer-Grouting-Silicone-Profiling-Applicator/dp/B07H8K5W8D/ref=mp_s_a_1_4? Where the shower screen meets the tray, clean the tray and bottom edge with C-tec Multisolve. Get some clear C-tec CT1. Read this, especially p3 "Fitted the glass today". Leave the thing to set for 36 hours. Seriously just walk way and don't touch.

I'd run a line of silicone on the wall and screw the channel onto that making sure it oozes out the screw holes. Then wipe ALL traces of silicone from within and outside the channel. Use cheap baby wipes for this, it works a treat. Do not block that channel with silicone. Any water that gets in there needs to be able to run downward. EDIT: I take no credit for the above. Seem to recall it and the baby wip tip, being the word of wisdom from @Nickfromwales.

You're on shaky ground making statements like that...

I think they had it right when I first used it circa 1998 judging by the performance of the stuff I've put in to date. It's on mains, hot and cold, HW & CH. Quite why they changed the detail I don't know. Just a bit chunky imo.

Posted in wrong place ?

Did some mods here 20 years ago when we bought the place all in the grey, chunky Hep2O. On the quick to get CH upstairs as there wasn't any, had the new baby etc. Copper pipe and all joins Hep2O. Not one fitting a problem. Stuck my finger in one of those serrated rings once...lesson learnt. Made one cock up more recently trying to swap innards between circa 1998 grey Hep2O and the newer stuff. Looks similar but a bit more streamlined. It leaked but didn't burst. My fault that.

You can all go and do one! It's the one half decent bit of this place! ?

I did seriously look at those click together formers. Really, really happy mind with how mine came out.