Cob beehive – an experimental top-bar hive adaption

the cob-lined hive. Note the comb from another hive being used as a template.

One of the key pieces of advice for any new beekeeper is to have at least two populated-hives. In the event that a hive becomes queenless, brood-comb from another can be moved to it (so the bees can raise an emergency queen). Or if any colony is low on stores, a frame of honey can be transferred. But to gain any benefit from multiple hives, the parts need to be interchangeable – having a warre hive and a top-bar hive is interesting, but you can’t easily move combs from one to the other.

Earlier this year, I got a second top-bar hive. Although it was the same type as the first one, the size and shape were different. It was wider and deeper, so although it would be easy to transfer combs from the old hive to the new one, it would not be possible to move them the other way. I knew that that if I ever needed to move comb, it would inevitably be in the more awkward direction.

The new hive was also more steep-sided than the first. Wax-remains on the walls of the hive showed that its previous occupants had built a lot of brace-comb – the colony had attached their combs to the edge-walls of the cavity rather than leaving them free-hanging from the bars. These wall-attachments make inspections more difficult and disruptive, and are a sign that the wall-angles are wrong – a properly-shaped hive will minimise the amount of brace-comb.

crossection

Diagrams showing cross-sections of hives. In hive (a), the comb hangs freely from the top bar. In hive (b), the bees have built brace-comb (red) to attach the comb to the walls. Hive (c) has a cob-lining (purple), so the cavity better-matches the natural shape of the comb.

My plan was to narrow the cavity – adjusting the dimensions to make combs interchangeable between the hives, and creating a shape which reduced the need for brace-comb.

the cob-covered interior of the hive, during construction

Rachel Hammond, of the Incredible Edible Oxford Project, builds beautiful pizza-ovens from ‘cob‘. Cob is a traditional building material, a mixture of clay, sand and chopped straw – it’s now commonly used for outdoor pizza ovens, but cob (and its close-relations wychert and adobe) have been used for hundreds of years to build houses, churches and mosques. Rachel suggested that a cob-lining might be an effective way to change the shape of the hive.

To make cob, take clay and sand in an approximate 1:9 ratio (one part clay to nine parts sand), and add a handful of chopped straw. Put it all on a tarpaulin, and stamp around on it for about 20 minutes, until it’s well mixed (you should look like someone’s embarrassing uncle dancing at a wedding disco).

Barefoot in the garden on a cold April evening, we stomped about on clay and sand. To tell if it’s sufficiently mixed, press a handful into a ball and drop it from waist-height. If it stays together it’s ready to build with; if it falls apart, press repeat on your “eighties disco” playlist and keep dancing.

the almost-finished hive

For a pizza-oven, you make a circular wall of bricks and then build upwards, making each circular-layer slightly smaller than the previous one. For the hive, we built up from the floor, making a solid wall of cob on each side. A comb from the old-hive provided a template-size that we could work to, and a long dowel allowed us to keep the same profile along the length of the hive.

The flight-holes were on the long-edge of the hive. We constructed a small wooden tunnel, which we then built the cob around. It would have been possible to do this more elegantly, but I wanted to minimise the risk of a wall-collapse blocking the hive-entrance in any way. Although the tunnel interrupts the profile of the wall, it reduces the chance of the entrance being blocked by fallen-cob.

For drying a cob oven, a fire is lit inside to dry and harden the clay. I was reluctant to light a fire inside a wooden beehive, so I left it open on hot days to dry in the sun. This seemed to work. I am hoping to populate the hive in the next few weeks, and I’ll update here when I know if it was a success. [update October 2017 – the hive now has bees in it].

Some possible advantages and disadvantages of cob-lining are outlined below…

Advantages:

High Thermal Mass
The position is cold, and a cob-walled hive will have the same advantages as a thick-walled house – a high thermal mass means it should remain cool in summer, and retain heat in winter. Although it would take more energy to warm ‘from cold’, it should be good at maintaining a steady internal temperature, which is what the bees need.

Oxgrow Oven

a cob pizza-oven at OxGrow Community Garden, Oxford

Sustainable Materials
The materials can be dug from most gardens. There’s minimal carbon-footprint, and no ‘waste’ materials. If it ever needs to be recycled, it can be broken up and crumbled back into the ground.

No tools or skills required
Aside from a bucket, building with cob needs no tools. And although there’s some skill in knowing when the mixture is at the right consistency, it’s a forgiving material and doesn’t require the same experience or knowledge as building with wood.

Reversible

Another advantage is that it’s reversible – if the experiment doesn’t work, I can chip the cob out, and still be left with a functioning hive.

Disadvantages:

Weight
The main disadvantage is that it’s heavy. Really heavy. There’s approximately 30kg of sand in the finished hive, a few kilos of clay, the original woodwork of the hive. It’s not a thing for moving around, but for my static, garden-based setup that’s not a big problem.
As an advantage, it’s not going to blow over in the wind, nor would it be possible for anyone to steal it.

the finished hive, in situ

Danger of Collapse
If the cob-walls were to fail, there’s a slight chance that they could block the entrance, trapping the bees inside. Although the entrance-tunnel tries to avoid this, it’s a risk which wouldn’t occur in a traditional wooden-built hive.

Brace comb
If the bees do build brace comb, it will be more difficult to cut it from a curved cob-wall than from a flat wooden surface. Particularly around the entrance-tunnel, it might be quite messy to remove the frames for inspection.

Unknowns
The other disadvantage is that there are so many unknowns. We don’t know how the walls will respond to the humidity inside the hive. We don’t know about airflow. And we don’t yet know how a bee colony will react to living in a cob home. With this experimental setup, I hope I can answer some of those questions. I’ll post an update here when I have some answers.

Jack Pritchard, Oxford, May 2017

🐝 🐝 🐝

Advertisements
This entry was posted in Experimentation, Hives, TBH, Technology, Uncategorized and tagged , , . Bookmark the permalink.

One Response to Cob beehive – an experimental top-bar hive adaption

  1. Pingback: New Arrivals: The Rat Box Bees | Oxfordshire Natural Beekeeping Group

Leave a comment ...

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s