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Mould inside my flow hive!

We’ve had a lot of wet weather down in NSW Northern Tablelands where I am and my Flow Hive has been outside. I have organised to pick up a nucleus next weekend so went to check my Flow Hive to make sure all was good and there is a lot of mould on the inside of the roof (pictured) and also inside the brood box (also pictured). None on the super as I didn’t put that outside.

I painted the outside of the HIVE with one coat of undercoat and then 2 x coats of outdoor paint but read online that you shouldn’t paint the inside of the hive. Should I have painted the inside to prevent mould growing? Any other suggestions how I can get rid of this mould and prevent it in future?


Hi Bridget, I never had mould on the inside but it is pretty dry here. I prefer mine bare timber inside, with no chemicals, and no paint.

If it was mine, I would kill the mould with some diluted bleach. Then wash it and dry it completely. Then I would rub some beeswax to try to hide any lingering smell. ideally, you would air it for a few days before you introduce any bees.

I don’t know whether any residual bleach smell will affect the bees, so please before you take my advice, wait and see what others will say.


Hey @Bridget_Ann, welcome - not pretty, but good you found the problem before it gets much worse. I think @Zzz describes a good solution, just use the smallest ratio of bleach to water when you scrub, or consider using white vinegar instead and drying in strong sunshine.


It doesn’t if it just smells like a swimming pool. Bees around here love to drink swimming pool water! :blush:

I think the bleach idea is a good one. Using a solution of 4% household chlorine bleach in water is great for killing mould. Scrub it in, leave for 10 mins, then rinse off and leave in the sun to dry as @Eva says.

Mildew inside unoccupied hives is very common. The bees actually don’t care very much about it. They will clean up and wax as best they can, and ignore the rest. It doesn’t hurt them at all.


Mold is common in a hive that doesn’t have a colony in it, I think because of a lack of air flow thru the hive… I use white vinegar, rather than Chlorine which is bad for the environment, to kill the spores and mold, I don’t wash it off and just let it air dry. Bees don’t seem to offended by the smell. Once there is bees in the hive the mold won’t return normally unless you have long periods of humid weather, but I guess that doesn’t happen much in Armidale. :smiley:.


Going by this photo, it appears that hoop pine doesn’t hold up to moisture very well.

My strategy for hoop pine is to treat it with copper naphthenate before letting it thoroughly dry out. Then I’d give it 3 good coats inside & out with good quality house paint.

You’ll read plenty of advice saying not to paint the inside of bee boxes. I’ve never had any adverse effects of internal painting of bee boxes. Just let the paint cure for a few weeks before putting bees into the hive.



The issue in using copper naphthenate and painting the inside of the hives is with the bee keeper in not wanting to allow for enough drying time. Doing boxes the way you describe would greatly extend the life of the wood ware. I remember a commercial bee keeper who mixer Copper Naphthenate with maybe mineral turps and would soak the boxes for several minute before stacking a shed full of boxes for a month then completely paint the boxes inside and out, I’m sure he wouldn’t have gone to the trouble if it wasn’t worthwhile.
Hoop Pine is vulnerable like most timbers to the end grain soaking up any moisture from capillary action.
Now your making me think about painting my boxes on the inside to extend their service life. Thanks Jeff :laughing:

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I paint the inside and outside corners and anywhere where moisture can find it’s way in, including end grains, with a 1:1 mixture of water and quality exterior PVA glue. I use the brand Gorilla and find it excellent and is non toxic.

I give a couple of coats of the mixture and make sure it soaks in the joints then I paint the outside and edges.

Only been beekeeping since 2017 but so far they are holding up very well and have no sign of any water ingress.


When I get out and about visiting newer bee keepers who are having an issue or just want some tips and advice I am amazed to find so many hives where the owners have put a lot of time and effort into painting the outside of the boxes and the top and bottom edges are still unpainted. With some rain the water can sit there for days or even weeks and not evaporate.
I was suspecting Copper Naphthenate would be had to find but my local hardware store has it in stock so I’m going to begin using it with my boxes in the future. After seeing it in use for bee hives so many years ago I don’t know why I hadn’t adopted using it in the past. A case of not making the time to do research I guess. Thanks for the jab with the cattle prod @JeffH
Wow, the humidity this past 2 weeks is extreme but the rain is fantastic to get and great to see it is so wide spread over the Eastern States. It has to be taming down the bush fires so they can be contained and finally put out.

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G’day Peter, funny you should mention painting the tops and bottoms of boxes. I use BONDCRETE, a water soluble sealer, mixed 50/50 with water, then brush on two coats inside and out, when dry looks like a plastic coat, then I paint it with water soluble paint on the outside and bottom/top. In two years I’ve been doing this, have had no issues with it yet. My first hive I didn’t paint in this manner, but I soon discovered water egress at these joins were an issue, so my second box and any future boxes will all be painted top and bottom edges to assist long levity and prevent water egress. I’ve just read the bit about Dawn replacing her Flow hive roof, and thought it a good idea. BUT am unawares of where in Ozz we obtain the material. We do have something similar and I intend to investigate this shortly at STRATCO who sell insulated metal sheets in various thicknesses. One sheet should cover my requirements amply. May even make two, one for my second Flow hive that has a standard lid. Stay tuned to see the results.

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At the local Men’s Shed we us a lot of Bondcrete for sealing timber that they want to appear natural timber like a raised garden bed for example.Thanks for your idea Ed, well worth thinking about. I use water base paint also and with 3 heavy coats I get 6 to 8 years minimum before a re-coat.
My local hardware store as well as Bunnings sell sheets of gal metal that you can make 2 migratory roofs from with a little left over. I make my own migratory roofs and all the makings are readily available. Any bee keeping supplier will have migratory roofs in stock but I enjoy making my own on a wet day.
Cheers Ed

Water egress is probably a good thing. You might have meant to say “water ingress”. You’d want to prevent water ingress.


It look as if that hive is varnished? I have two hoop pine flow hives- I wax dipped them both- and they are both standing up very well two years in. But the wax penetrated the wood 100% driving out all water. From what I have seen on this forum it appears that there are very few if any clear-coat finishes suitable for beehives that allow you to have a natural timber finish. basically if you want natural timber you have to get a cedar hive- and/or hot wax dip. Pine rots very fast outdoors if left int he weather. the hoop pine is supposed to have some antimicrobial qualities- but not enough to protect it from wet weather. In that photo it looks as if the water has gotten underneath the varnish and started to rot out from the inside. The varnish would actually make it harder for the timber to dry out I am guessing. Recipe for disaster?

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I think I saw that photo of the pine hive in another thread by another poster. It was determined that the problem was a coating failure not the wood. Varnishing a hive is not a great idea in my humble opinion.

basically if you want natural timber you have to get a cedar hive-

@Semaphore yes that’s exactly right - with the Western Red Cedar you can retain the natural timber look by treating with linseed oil, tung oil, etc. instead of painting it - for the Paulownia and Araucaria (Hoop Pine) hives we 100% recommend painting the hives with two coats of quality outdoor paint for protection and durability.