Teeth2k, Hi again.
Have a look @ the post above from Conny Ref contact the L/Authority.
Back in the day, the ducting could be composed of various, at times materials that did contain Asbestos.
As for the actual material of the ducts, that would and does vary dramatically even within one Council area, never mind Nationwide.
The duct material could be a fairly robust board anything from 12.5. MM thick up to as in your post 50.MM thick, the composition of the material, sorry but this is also highly variable but the inner surface will be absolutely filthy, the outer surface will have builders debris all over it and loads of dust. Internally this material will be an off white, and as posted fibrous in nature, difficult to describe, but not un like a soft board like Cellotex? if that means anything to you?
The material was easily cut with a Saw and easily marked with a Hammer that is when struck with a Hammer an indentation would be visible, the duct material can generally be snapped by hand.
just in case this material does contain Asbestos, seal it off, don't cut it and contact in the first instance the Local Authority who probably have records.
