On Sun, 1 Nov 2020 09:55:56 +0000, Andy Burns wrote:

a 1/4" tongue of weetabix doesn't have much strength,

True but the T&G on weetabix is more like an inch and half with
quite
on offset between sides and the toungue/groove tapered.

My loft boards are 3/4" (green flooring chipboard is 22m or occasionally
38mm).

https://www.homebase.co.uk/chipboard...-1220-x-320-x-
18mm-3-pack_p404607

Er, so? You can clearly see the T&G that is much more than 1/4",
maybe nearer an inch on those boards, and the taper.

--
Cheers
Dave.