Steico Internal Wall Insulation advice

[Mulder]

Hi all,

I'm considering installing internal wall insulation to the ceiling and walls of my cottage. It's a half height roof, so the only thing separating the bed from the stars is a layer of lath + plaster and some old clay tiles.
I am planning to install 60mm of Steico ProtectDry to external facing walls and finishing with lime plaster.
Has anyone done this and can offer advice?
From what I can tell, I don't need a vapour membrane or anything, just mix up the adhesive (lime based?) and apply to the existing plaster walls. Is this correct?

I'll use some mechanical fixings through to the roof joists where possible too. Based on the photo below, should I use 120mm or 140mm fixings?

I was considering the T&G Steico panels so they mate together for a stronger finish. Why do people ever use the square edge? What's the benefit?
I'm assuming the boards are relatively easy to cut with circular saw when I need to butt against a wall?

The photo below shows a handy cross section.

 

[Kearn]

The edges of the boards where thinner have a tendency to break easily. So be careful when they arrive as being strapped on pallets results in failed tongues/grooves. They don’t frankly need to interlock, butting is just fine as you’ll plastic mesh over the join anyway.

Correct, no membrane.

The adhesive is isn’t really breathable, if I recall, it has some plastic content to help it stick, which negates the benefits a bit. You’ll struggle to get any adhesion to old plaster though with lime. But if the existing lime is smooth/flat then there’s no need, just screw them as intended and they’ll sit flush. But this isn’t a ‘where possible’ approach, it’s as required at the specced quantity per board. Especially when on a sloping incline. They’re heavy and must be mechanically fixed. I believe 35mm is the minimum specced depth into the background, but if you can go more, it’s not a bad idea.

All of this, can be discussed with whoever is supplying - where are you sourcing?

They’re not great for plastering onto, limited key, especially when getting into above head territory. So you’ll want a nice sticky mix, such as a fine hemp.