Concrete nest boxes

Playing around with a design for an all concrete nest box now, having read the studies that Benn linked in another thread. It does seem as if the Schwegler "woodcrete" boxes beat all others in multiple studies, when put side by side with wooden ones, so I have loosely based my first design on one of their more popular ones. 12cm circular chamber, 28mm hole placed slightly higher (16cm centre to bottom of inside, old boxes 12cm) because studies showed that they prefer that over shallow. The concrete I am using is made with perlite as the aggregate, which is inert (and safe), very light and provides great insulation - an inch of this concrete is more like 5-10 inches of regular concrete, apparently. So similar to woodcrete in that respect, but easier to work with I think. This mix is supposed to be quite porous and breathable, too, but I plan on drilling one or two holes in the base for draininge as well. Glass fibres added for extra strength - this should be very strong.

Pics below of the first casting. I have made a 12mm inset at the top so that I can build a 12mm plywood lid that sits snugly, to house the camera and lights. Another feature here is a relatively low ceiling above the hole - just 5cm from the centre of the hole. The sides are 3cm thick where the hole is. Now planning a three hole version as well so watch this space



inside:


mold: