This FAQ post tells you everything you need to know about Woodcrete and its uses in bat and bird box construction. If we’ve missed something off (hopefully not) please let us know and we’ll update it.
Woodcrete - what is it?
A quick definition then:
Woodcrete: “A mixture of wood and concrete”.
Not too complex – it’s a simple combination of two basic materials. Often the wood can be waste material, rather than prime timber cut into tiny pieces.
According to Homebuilding & Renovating, “Woodcrete was first developed and patented in Switzerland in the 1930s by the company Durisol, the name still predominately associated with this building system across the world”.
Initially used for civil engineering projects, today Woodcrete is widely used for building work, for garden products such as bird tables and many other applications, particularly where durability is key. Of course for this FAQ post we’re particularly interested in its uses for bat (and bird) boxes.
Woodcrete is also known as Woodstone®, which is a trademark registered and used for the Vivara Pro range of nest boxes. It consists of concrete mixed with wood fibres.
Why use Woodcrete?
There are many reasons for building a bird or bat box out of Woodcrete (as opposed to wood or some other material). Let’s run through them…
Woodcrete provides a much more stable environment inside the bird or bat box than wood. It insulates the interior from extreme temperatures and, in today’s weather incidents of unexpected heat waves and “beasts” from various compass points, this is a blessing for the box inhabitants. It keeps them cool in the summer and cosy in the winter.
The material is breathable/porous too, which also helps with maintaining the stable environment inside.
Woodcrete, unlike wood which is mostly smooth, has a rough surface which makes it easier for bats to cling too. This means the interior shell of the bat box is a useful surface for them, in addition to any panels and crevices that may be fitted inside.
As you know, wood eventually rots. Hardwood might take longer than softwood to do this, but wood will break down. Treating wood will hinder this of course and great care must be taken to ensure the wood treatment doesn’t affect the bats – they are very sensitive to chemicals and paints etc. Woodcrete, on the other hand, is a long lasting material (practically weather proof) that means the box will be available to bats for years (make that decades) to come.
Although the initial outlay for a Woodcrete unit tends to be higher (compared to wood), its durability means the box is replaced less often. This cuts down on replacement costs which include labour, transport and moving cumbersome equipment (ladders, ropes & tackle) back and forth. Where a box is self-cleaning (with any droppings fall out of the base of the unit), it’s practically fit and forget.
Ease of Use in Building Construction:
Appropriately shaped bat boxes made of Woodcrete can be incorporated into the building and even rendered over.
Does wildlife prefer Woodcrete over wood?
This is an interesting question. We’ve found that the answer has been yes for songbirds, although in one case this may be down to status quo bias.
According to ConservationEvidence.com:
1) A US-based study (in 1996-1997) found that 90% of nesting eastern bluebirds Sialia sialis (102 pairs) chose Woodcrete boxes rather than wooden boxes. When given the choice to move to a clean wooden box, 73% of pairs chose to remain in their soiled Woodcrete box.
2) A replicated trial in arable farming landscapes in Norfolk, England, in the summers of 19972001 (Browne 2006) found that tits Parus spp. nested in a higher proportion of hanging woodcrete boxes (38% 48 boxes occupied), compared to tree-mounted woodcrete boxes (25% of 48) or thick and thin wooden boxes (20% and 16% of 48 boxes respectively).
3) A 2002-2006 trial in Toledo suburbia in Spain, found higher tree sparrow Passer montanus occupancy rates, and higher reproductive success in woodcrete nest boxes, compared to wooden ones (average of 76.5% of 50 woodcrete boxes occupied and 81% success for 152 clutches vs. 33.5% of 50 wooden boxes occupied and 79% success for 68 clutches).
Can I make my own Woodcrete?
Well yes, but why would you re-invent the wheel?
Schwegler and Vivara Pro have built their bat and bird boxes to specific dimensions with internal sections designed for particular species. They are constructed from tried and tested components that have been proven to work successfully. As mentioned earlier, bats are particularly sensitive to chemicals – getting the components wrong could mean a box with no occupants.
The Bat Conservation Trust points out that Woodcrete bat boxes tend to be one of two shapes:
Cyclindrical for hanging by a wire loop from branches of trees. They tend to have an access hole at the front.
Box shaped for affixing to trees, and flat surfaces (buildings & walls). Entry is often via a slit at the base.
- Cylindrical for hanging by a wire loop from branches of trees. They tend to have an access hole at the front.
- Box shaped for affixing to trees, and flat surfaces (buildings & walls). Entry is often via a slit at the base.
Woodcrete has many advantages over wood for use in bat and bird box construction and in some studies it was found to be preferable to songbirds when offered a choice. We’ve yet to find a study that indicates bats prefer one or the other.
That wraps up our focus on Woodcrete. Please do let us know if there’s some facet of this material you’ve come across that would be useful to other ecologists.
Before we go, one last point, which is always worth repeating:
Bats are a schedule 1 protected species under the Wildlife & Countryside Act. It is illegal for any member of the public to disturb a roost, handle or kill any bat. Bat boxes, therefore, may only be inspected by a licensed bat worker.
"What is Durisol?" Homebuilding & Renovating, Future Publishing Limited, 6 Oct. 2016, www.homebuilding.co.uk/what-is-durisol/. Accessed 8 Mar. 2019.
"Nest Box". En.Wikipedia.Org, 2019, https://en.wikipedia.org/wiki/Nest_box. Accessed 1 Mar 2019.
"Action: Provide artificial nesting sites for songbirds - Item 41." ConservationEvidence.com, www.conservationevidence.com/actions/498. Accessed 8 Mar. 2019.
"Action: Provide artificial nesting sites for songbirds - Item 49." ConservationEvidence.com, www.conservationevidence.com/actions/498. Accessed 8 Mar. 2019.
"Action: Provide artificial nesting sites for songbirds - Item 57." ConservationEvidence.com, www.conservationevidence.com/actions/498. Accessed 8 Mar. 2019.
Bat Box Information Pack. Bat Conservation Trust