We made a little bit of progress this weekend, adding the base insulation layer. We used perlite with a bit of clay slip to bind it; and embedded glass bottles to economize on the perlite. Anther commonly used material is sawdust and clay slip – but it doesn’t insulate nearly as well as perlite and can crumble if the ratio is not right.
The paper collar prevents loose perlite from falling through the wire cage. Eventually that part will be covered by finish plaster and be hidden from view.