Wooden bee boxes are a long-term investment. If properly prepared and cared for they should last for many years, if not decades.
During the big push to get bee equipment ready for the season, it’s tempting to just deploy unpainted woodenware. That works, but doing so shaves many years off their service life: the box joints may warp open and the sides may develop cracks due to constant weathering. Even with a lot of rehab later, these boxes may never be as nice as if they had been protected from the start.
Seal the exposed end grain of the box joint fingers, the handholds, the edges of the box and any knots. You can do this by either using one or two coats of a good exterior sealer such as Zinsser 1-2-3 BIN or by brushing on a coat of exterior wood glue such as Titebond II or III over these vulnerable areas.
Always paint only the outsides (and edges, if you wish), not the insides of the boxes.
Coat the boxes with a good quality exterior primer. If you can find it, an oil (alkyd) exterior primer is best, even if you plan to use latex paint for the top coats. In some states, oil paints have been removed from the market for air-quality reasons. But an oil-based primer has superior stick-to-the-wood qualities.
Apply two coats of a good quality, exterior, latex top coat paint.
You can sand between any of these coatings, but it may not be necessary for bee boxes. Just make sure the previous coat is dry and clean before adding another coat.
Let the boxes dry and air out (off-gas) for as long as possible after painting, both to make them easier on the bees (less chemical exposure for them), but it also allows the paint to cure fully. Latex paint takes a notoriously long time before it is completely cured and will not stick to adjoining surfaces. Curing time is much longer than the dry-to-the-touch time, or even the recoat interval. Curing time is particularly important for bee equipment that is stacked up in a hive assembly. Uncured painted edges set on top of each other can stick together so forcefully that it becomes extremely difficult to separate boxes, resulting in damage in prying them apart. Nothing ruins a pleasant afternoon of bee work more than having a huge struggle to separate the boxes.
The best work-around for long curing times is to get your boxes painted early enough so that they have at least 30 days to fully cure before they’re needed. The other thing you can do is to leave the edges of the boxes unpainted. But that also leaves the edges unprotected if the boxes are not perfectly stacked-up every time. You can hedge your bets a little if you use the Zinsser product on the edges, even without additional coatings. But the best practice is to get your painting done early enough to allow for a long curing period afterward.
A handy way to have the whole box, including the edges, exposed for painting is to hang the boxes from a pipe supported between two saw horses or step ladders. Then you can just rotate the box around the pipe as you finish each side.
If you want to spray paint the boxes, do it with several of them stacked up together. You need to separate them as soon as they are dry to the touch to prevent the paint from gluing them together as they finish drying. You will still have to hand paint the bases, and outer covers.
If you think your boxes are getting a little stained and dirty while in use, you can scrub them with a brush and warm water, but not soap, without taking them off the hive. If you do this during a rain storm, the bees inside will hardly notice. If they need more intensive cleaning than that, swap them out temporarily and do the work away from the hives.
You can touch up dings to the paint while the boxes are in use, too.
Many beekeepers choose their hives’ paint colors by buying “Oops” paints that were mistinted at the paint store. These can often be found at a substantial discount. But don’t be tempted to throw money away on interior paint, even deeply discounted interior paint. The time and work involved in painting bee boxes warrants good quality, exterior paints that won’t fail prematurely.