BLO finished wood getting mildewed in a cold workshop

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Wrongfoot

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I recently re-started some cabinet making once I finished a build project. it's nice to be doing something less industrial.
I refurbished a few planes, chisels and tools I picked up from ebay, as most of my hand tools were sold a while ago I needed new items. I did as I had previously and stripped the finish off the wooden parts of the tools and treated with BLO as I quite like the feel of the wood in my hands rather than a polyurethane/plastic finish. I've run into a spot of bother...

My workshop is pretty much a barn it's dry enough and sound but cold and as damp as the weather I guess. This isn't problem none of the beams or stored timber have ever suffered, it's too dry for rot or woodworm. The stuff I treated with BLO is getting mildewed (I think?) It looks like a surface mould not a fungal mycelium. Wipes off ok but comes back. None of the tools had any sign of mould fungus when I refurbished them. My guess is the cold damp weather is giving enough moisture for the mildew to grow on the BLO oils in the wood. Anyone else had this?

It could be that the BLO hasn't cured dried properly in the cold and still is too liquid in the wood or it could just be that BLO isn't a good choice for anything left in an unheated workshop. What would you guys do? I could bake out the wood indoors to cure the BLO properly, but if the mould can grow on the hardened oil that'll not solve it. I could degrease the surface and seal up the tools with a varnish? I could do both?

Is this a known issue with natural finishes? It's only happening on the stuff I treated with BLO and never happened in my previous warmer workshop? Bare timber is fine anything painted is fine, mdf and ply stores fine.
 

Rorschach

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The mould is feeding on the oil, I have seen it plenty of times before on oil treated wood and leather. Neats foot oil treated leather is particularly bad for it and I ruined several items before I found out the advice I was given was bad.
 

AndyT

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I've heard it mentioned as a problem and seen it occasionally. As you say, it wipes off ok. I've not had it recur but my workshop is dry.
It's easy to say, but the real answer is to have a workshop without that big awkward problem of condensing dampness - I expect you'll see metal parts going rusty as well.
Failing that, vinegar might help.
You could also try applying wax on top of the oil. Microcrystalline wax is generally recommended as it gives a clear thin layer with some protection. Not the cheapest but a small tin is a lifetime supply for most of us.
 

John Brown

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Interesting. I was planning on using raw linseed oil on the exterior surfaces of our oak windows and dooes. Maybe I need to rethink. Whatever the water based stuff the previous owners used doesn't seem to do anything.
 

ED65

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Wrongfoot":1wexi713 said:
I could bake out the wood indoors to cure the BLO properly, but if the mould can grow on the hardened oil that'll not solve it. I could degrease the surface and seal up the tools with a varnish?
The oil within the wood can be a problem. So it's not just if you haven't been as careful as you might wiping away all excess. And it doesn't seem to matter if it's had a good chance to cure.

Yes you can treat with shellac or varnish to prevent this (by providing a physical barrier between the moulds and the oil) but on wood that has already seen the problem you'd want to kill existing mould and its spores to be sure of it not springing to life again.

Wrongfoot":1wexi713 said:
Is this a known issue with natural finishes?
Not all, but with oils yes. Some oils are more prone to it than others and linseed is well known for being poor in this regard. It doesn't matter if it's BLO (whether heat treated or with added metallic driers) or "raw".
 

Wrongfoot

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Back from work and daughter finally asleep. Thanks for the advice everyone. :)

Definitely BLO a named reliable brand.
I'm not sure how to kill spores. Maybe a rub with Jeyes fluid?

I think I'll go with a good dry out indoors before degreasing and refinishing with a PU varnish.

PS. I'd love a warmer workshop, but that'll take money and time I don't have at the moment. I'll be avoiding natural oil based finishes on anything that will be left in there particularly in the winter. I guess I'm lucky finding out about the problem on a few tool handles rather than a bigger project. Also useful to know about the same problem with leather.
 

ED65

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Wrongfoot":gdmffvgl said:
I'm not sure how to kill spores. Maybe a rub with Jeyes fluid?
Vinegar as already recommended is actually a very good starting point.

The main thing with surface mould or mildew is actually to clean off the surface, to physically remove the mould as much as possible. So washing down/wiping more than once and changing your cleaning liquid periodically is vital. Obviously you can never be sure of getting every trace which is where a mildewcide comes in, to give an extra bit of effectiveness.

Bleach is worth a shot too and it's been recommended for this purpose in DIY circles since forever, but vinegar does work better in some cases. This is according to some written sources and I've run direct comparisons myself, where vinegar tends to do better; however neither is a sure-fire solution on wood.

Wrongfoot":gdmffvgl said:
I think I'll go with a good dry out indoors before degreasing and refinishing with a PU varnish.
FWIW you can get much the same look as oiling using a varnish by just thinning it down slightly to turn it into wiping varnish, and then applying two or three coats which you wipe back to nothing afterwards (so application procedure can be exactly the same as with BLO). Alternatively oil first to get exactly the look you like, then apply very dilute coats of varnish over the top.

Incidentally if you blend the diluted varnish directly with BLO you'll get something akin to commercial Danish oil-type finishes although it will tend to be slower drying.
 

John Brown

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I don't want to use varnish, as I'd like to be able to overcoat an oil based finish, as opposed to having to strip off flakey varnish and re- apply.
What does the team suggest for exterior oak? The Osmo stuff claims to block UV, but that boat sailed years ago as far as my windows and doors are concerned.
 

ED65

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John Brown":fdqnhe7k said:
I don't want to use varnish, as I'd like to be able to overcoat an oil based finish, as opposed to having to strip off flakey varnish and re- apply.
This doesn't really happen with just a few of coats of dilute varnish wiped back, it becomes a penetrating finish (no surface film to speak of). Try it on some offcuts and see the difference between different dilutions, wiping away some, all or none of the excess. Conversion to wiping varnish opens up a whole new world with varnish and it's been a total game-changer for many users, including pros.

Edit: sorry is this in relation to the next sentence, exterior use?

John Brown":fdqnhe7k said:
What does the team suggest for exterior oak? The Osmo stuff claims to block UV, but that boat sailed years ago as far as my windows and doors are concerned.
Line up 10 woodworkers, get 11 answers :) All I'm going to say about Osmo products is they're invariably an expensive option, and you can get similar (and sometimes better) things in each category while buying British if that's a factor you want to consider.

Anyway, since it's oak doing nothing could be a viable option. It is durable to very durable outdoors on its own and even after noticeably weathering it can have donkeys of life left in it. Plus, once you apply something to it you then have the upkeep schedule to worry about in perpetuity.
 

Wrongfoot

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ED65":1qbuz16x said:
Wrongfoot":1qbuz16x said:
I think I'll go with a good dry out indoors before degreasing and refinishing with a PU varnish.
FWIW you can get much the same look as oiling using a varnish by just thinning it down slightly to turn it into wiping varnish, and then applying two or three coats which you wipe back to nothing afterwards (so application procedure can be exactly the same as with BLO). Alternatively oil first to get exactly the look you like, then apply very dilute coats of varnish over the top.
Sounds a great idea. Is the choice of thinner critical? White spirit? Acetone? Must you match the thinner with the one in the varnish?

Thanks for the advice.
 

ED65

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Wrongfoot":1w4o820n said:
Must you match the thinner with the one in the varnish?
Basically yes. The one the tins say to clean your brushes in, which will be white spirit for varnish and other oil-based finishes including Danish oil, teak oil and trad enamel paints.

99%+ of varnishes are made using a solvent that is in effect white spirit, although it'll be called something else in the safety data sheets because there are numerous chemical names for solvents in this family.

You could also use turpentine, if you have it and you like the smell; no advantage to using turps for anything like this other than the smell which some people find pleasing.
 
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