Hi
I have one of my varnished pine supers experiencing a type of wood rot.
Is there something am or am not doing?
Is this a common problem?
A photo will definitely help.
Was it oil based varnish?
It tends to crack as it is not flexible, water penetrates under the varnish, and starts to rot.
I hate that stuff, and I always used marine varnish. There are some water based ones which are supposed to be more flexible.
Hi there and welcome to the Flow forum!
Do you have any photos? Inside and out would help a lot with working out where the problem is coming from. It would also help to know what type of varnish you used and when. Marine varnish lasts longer than interior, for example. In many climates, even marine varnish will only last a couple of years, unless you do multiple coats (5+ on my front door!).
I am sure somebody will be able to help. We have lots of knowledgeable people on this forum. 
It was 4 coats of marine varnish
How did you clean the brush, water or turps?
Oil based will get hard in the sun, and crack with wood movement and expansion.
I used Feast & Watson marine varnish on an outdoor jarrah table following instructions to the dot, and within two years it all cracked and had to be sanded back to bare timber. I now use either stain, or solid paint.
Welcome to the forum Philip and a good question. You haven’t said where on the box it is rotting but maybe it is on the end grain or on the top and bottom edges. For some reason lots of the folks forget to treat the edges and that is where rain water will accumulate and sit for ages and soak into the wood helping it to rot. If the varnish is oil based then a first coat of varnish mixed with some mineral turps will help it being able to penetrate the timber to seal the pores of the wood.
I’m a bit of a traditionalist with my hives, I use a water based white exterior paint, white to help keep the hives as cool as possible by reflecting the heat and water based so that on a fine day I can put 4 coats on in a day and the boxes can be put into use a day or two later.
A pic or two might help us to better give you advice and are you sure the timber is rotting and not having mold which is a more common problem with my hives and I’m only 100K’s away from you.
Cheers
Here is a picture.
The problem started with the roof which I replaced about a year ago and it has now presented as per this picture. I’ll add a photo of the inside once I’ve replaced it.
The Flow roof should be painted with a solid opaque paint, otherwise it won’t last long.
On the hive body, it looks like a coating failure. Is that the varnish peeling? Also, the joints, which I assume you varnished after the hive got assembled, are hard to properly seal out of water with varnish. When temperature changes, all you need is a slight movement, a hairline crack in the varnish, and water creeps in, and the rot will set. Once rot sets in, it will just spread, until you kill it.
I know it looks good when varnished, but if you really want longevity, you have to sand it back, treat the rot with something like bleach, fill those joints with a filler, and paint with a quality water based paint which is flexible. You can also stain it, but I still prefer paint for my climate.
The problem is that all this is hard if you don’t have a spare hive to swap until you fix.
Is that 6 or 7 frame flow. I have a 6 frame super you can borrow while you do repairs. It looks like a 7 frame super. Anyway I’m at Buderim.
I have a modified flow roof to go on top of the 6 frame super which would sit on a 10 frame brood box with the aid of a board to cover the gap.
Thanks Jeff for a kind offer. I have purchased a new one to replace this 6 frame one.
The damage visible is not just varnish but rotting in the timber.
Perhaps paint is the best way to go? I used tung oil on my original cedar boxes and they are good as are subsequent painted ones.
1 Like
I used marine varnish & cleaned with turps.
Took ages and allowed drying between coats - minimum 4 and expended effort sealing the end grains
You’re welcome Philip, seeing as it rotted so quickly, I’d stick my neck out & suggest copper naphthenate treating before painting. My first boxes I made, I think were radiata. Some of the boxes needed serious repairs after 10 years. While others lasted for 25 yrs before needing repairs, however only a few. About every 5 years I carried out major bee box repairs. I started treating about 15 or more yrs ago. None of those boxes need further repairs, except a couple where I didn’t cut enough of the dry rot out.
I wondered if hoop pine was better than radiata. After seeing your photo, obviously not.
That is definitely rotting from water being absorbed on the end grain of the timber. Only a guess but this might be a result of not applying a mixture of mineral turps and the varnish on the first application so it really penetrated and sealed all the pores of the timber before applying a few more coats of the varnish.
I would go with @JeffH 's advice about treating it with copper naphthenate and allow plenty of drying time.
I’m a die-hard white paint person and apply 4 thick coats to the outside and the edge on the top and bottom.
Cheers
1 Like
Thanks for the opinions and suggestions. It’s all very helpful.
Sorry for the late response on this, but I have a few more thoughts, which you may not want to take on. 
If you want to rescue that super for another go at varnishing, it may be possible. You say the wood is rotting, but if it is structurally sound, it might still be useful. I would consider the following:
- Take the super off the hive when possible and remove all of the Flow frames.
- Dry it out really throughly for around 6 weeks. Inside in an air-conditioned room near a fan would be great. Wood changes shape for up to 6 weeks while drying out, so leave assembled to keep it as square as possible.
- Sand the varnish off as much as possible, wipe with turps and sand again to bare wood. You can sand while it is drying, but wet wood sands differently (more comes off) from dry wood, so be careful.
- Treat the stained area with wood bleach (in the USA, this is oxalic acid powder and is available from any DIY store). That will lighten the stain and often will remove it completely. My wood restorer expert makes a paste out of it, and uses an old nail brush to scrub it in along the grain of the wood. Takes an hour or so of scrubbing and rinsing, but it works well. Wear gloves, by the way, it is quite corrosive! The bleach seems to kill the mould causing the rot too. Rinse well after the stain has faded acceptably.
- Once dry from the bleach (a couple of days) fill any splits or rot channels with a good quality exterior wood filler, and sand when dried.
You can then revarnish after a couple of days of drying, if you are willing to risk varnish again. If you are going to copper treat it and then paint, I would skip the bleach step. The copper should kill off the rot, and the wood bleach would just be more work. However, if you want to see the pretty wood again without the stain, bleach is the way to go.
Just a few more thoughts. I still think paint is the best for pine, but the rest of your hive is very pretty with the varnish, so you have to decide what you want.
Another option to save the rotting area is wood hardener. Once you’ve got rid of any mould and the wood is dry you coat with this.
1 Like