In Australia, bee boxes are usually made from hoop pine, which is an inexpensive soft wood. The only problem is that it is prone to wood rot in hot humid conditions. The result is that boxes that are not treated with fungicide may only last a few years before they fall apart. Most commercial beekeepers dip their hives in fungicide - either copper napthalate or copper-chrome-arsenate (CCA) to prevent wood rot. Another common technique is dipping the hives in hot paraffin wax to seal the wood.
As our main objective in beekeeping (and growing our own food generally) is to avoid exposure to toxic chemicals, the last thing I want to do is put copper napthalate or CCA in bee hives when there is a good chance that these chemicals will end up in the honey and beeswax that I want to harvest. Additionally, these are both pesticides, and can't be good for the health of the bees either. Paraffin wax is better, but still a product derived from petroleum and hardly natural.
When we made our first set of hive boxes about five years ago, we painted them with self-priming water based exterior paint. We are now seeing significant wood rot in most of the boxes and they all need to be replaced. We were hoping that these boxes would last for 10 years or more. If we have to keep replacing boxes, then beekeeping is going to become an expensive hobby! So we were keen to find a better way to treat the hives to make them last longer, while still avoiding toxic chemicals.
Dipping the hives in beeswax and linseed oil
Wood rot is caused by fungi, which thrives in moist wood and warm temperatures. Wood rot can be prevented by either killing the fungi (using a fungicide) or reducing the water content of the wood.
A more natural alternative to dipping copper napthalate, CCA and parafin wax, is dipping in a mixture of hot beeswax and linseed oil. This works by forcing the moisture, sap and air out of the wood and replacing it with the water-repellent mixture of linseed oil and beeswax, which sets hard at ambient temperature. (You can read more about wax dipping generally here)
This technique is not usually recommended due to the cost compared to the other methods. For commercial beekeepers this is a significant consideration, however for the backyard beekeeper just wanting to avoid chemicals, this is cheaper than replacing hive boxes every five years.
We used a ratio of 5-10% beeswax in raw linseed oil. Pete made a vat just bigger than the longest side of the beehive box. He set up a small LPG burner under the vat to heat it to around 160degC. Each side of the hive box was rotated into the liquid for about 10-15 minutes. The water loss was visible as it bubbled through the oil each time a new side was submerged.
Water-based vs oil-based paint
There is significant debate and confusion amongst beekeeping books in my bookcase in regards to water-based versus oil-based paint. Fortunately I had already read about this topic when researching how to paint our secondhand house. (For more information, see this book on Queenslander house restoration)
Water-based paint forms a layer of plastic on the surface of the paint, whereas oil-based paint fills the surface of the wood. The problem is that water-based paint seals the wood too well, any moisture trapped in the wood cannot escape and will cause rot. While oil-based paints don't last as long, they do allow the wood to dry, and so they are the better option for painting any wood exposed to the weather. (We used oil-based primer on all the new chamferboards installed on our house during our renovation).
Many beekeeping books in my collection recommend the use of water-based paint, some even claim that primer is not necessary. In some cases, the authors are not located in sub-tropical/tropical locations that are prone to wood rot. Other authors recommend fungicide treatments and therefore can get away with water-based paint.
If you are going to use beeswax/linseed oil treatment, then oil-based primer is essential as water-based primer will not stick to the wood. You could then use a water-based top coat, but we have chosen to use oil-based paint for both primer and top coat.
Oil-based paint is inconvenient for clean up, as it requires turpentine rather than water, however if you paint several hives at once, it can be worth the effort. It also takes longer to dry, so you will need somewhere undercover for hive boxes to dry for several days.
Another area of debate is around whether to paint the inside of the hives. I would think if they have been treated in fungicide it would be essential to paint the inside of the hives to minimise exposing the bees to these chemicals. If you have used only natural products to treat the hive then there is no need to paint the inside as the bees will happily fill any gaps with propolis and make themselves comfortable inside.
Plastic beehive boxes
The other solution we are trying is moving away from wood hives completely. Although I generally avoid single-use plastic, I do think that plastic has a role as a durable, light and strong material. I have ordered two sets of bee hives from Nuplas, including brood box, full super, ideal super, lid and a bottom that incorporates a trap for small hive beetle. (read more about small hive beetle control here)
We are trialling these Nuplas hives next to our new wooden hives as we are curious to see how they both last in the weather and how the bees like them. So far we haven't noticed any significant differences apart from the small hive beetle trap being a very convenient way to help the bees remove beetles from the hives.
What have you done to treat or paint your hives to suit your climate?