Outdoors charred oak and tung oil

[wood_i_rather]

Hi folks,

I need some advice treating charred oak with tung oil so that I get a glossy finish/ the wet look. I hurriedly tried some test wood with thin layers but I ended up with a matt finish. I'm running a bit out of time (weather wise) and cannot do other tests, but hopefully someone here can help. I looked up on wikipedia and apparently you can only get the glossy look with polymerised tung oil (final coat), but it only seems to be sold in the US.

So far I've sanded the oak (originally rough sawn), charred it with a torch, brushed it, sanded it and treated it with a 1-1 sunflower oil and mineral spirits. This was a 4-5 weeks ago.

One hour ago, I put on a generous layer of 1-1 liberon pure tung oil and mineral spirits (did not wipe it yet). Where do I go from here to get as much gloss as possible out of the oil I have? Ideally I'd like to get as close as possible to how it looks in the attached pictured with a fresh coat of the tung mixture.

Cheers

 

[MikeG.]

Oil.....oak.......outdoors.........

Whatever variation you choose on this theme you are liable to end up disappointed.

 

[Sgian Dubh]

Where do I go from here to get as much gloss as possible out of the oil I have? Ideally I'd like to get as close as possible to how it looks in the attached pictured with a fresh coat of the tung mixture.

It's never going to happen with any kind of oil, whether it be linseed oil (boiled or raw), nor any form of tung oil, nor oils modified through the addition of a resin as found in the form of Danish oil or teak oil, etc. None the finishes just described are able to provide any significant protection to wood sited in exterior conditions for any length of time, a few weeks or maybe months at most.

I'm assuming from the way you framed your question that I've understood correctly and you want this item sited outside to face whatever the weather and sunlight throws at it. That being the case, probably your best option would be a long oil gloss varnish (a high quality yacht varnish such as Epifanes). You'd be committing yourself to a never ending cycle of maintenance, probably once or twice a year, much the same as those highly dedicated yachting types that seem to be forever rubbing down and revarnishing all their brightwork. Even that won't prevent ultra violet light doing a number on the charred wood surface and bleaching it out to grey over a couple of years.

If you want it black, your best bet might even be to simply paint it black using a good quality paint, gloss if that's the preferred sheen, and then you'll need to maintain the finish from time to time as normal to keep it looking tidy. Paint has pigment bound in resin, and this forms a physical barrier between the wood and the atmosphere surrounding it, and so long as the paint film isn't broken, it provides the best protection.

One option would be to put no finish on at all. The charred wood surface will gradually go grey, there's no time hungry ongoing maintenance required requiring some commitment on your part and, being oak, the wood is naturally durable, i.e., it'll last for many years, maybe twenty or more, mostly ignored and exposed to the weather and UV light. Slainte.

 

[AJB Temple]

Are you aiming for a shou sugi ban look? I have experimented with this myself and researched it a bit. I suspect to get a truly black look, you will need a much deeper char - the outside needs to be burned, not just coloured. Even then, I have never seen anyone achieve a long lasting gloss look by using oil.

There are loads of you tube vids on this, and most of them are from weekend wood warriors who are playing at it. Some people get it right - I recommend this video from Mr Chickadee. He does a proper burn:

 

[Fitzroy]

That does look lovely! My experience is any exposed horizontal surface outdoors takes a pounding from the weather and sun. Any finish you apply will require regular maintenance to keep it looking how you want. I recently completed an oak gate and finished in Osmo UV Oil. I only did this for vanity as I wanted some nice photos of an oiled gate. However, It'll now be left to weather, and eventually go grey, and in 12months it will look worse than if I had never applied the UV oil in the first place.

 

[wood_i_rather]

It's never going to happen with any kind of oil, whether it be linseed oil (boiled or raw), nor any form of tung oil, nor oils modified through the addition of a resin as found in the form of Danish oil or teak oil, etc. None the finishes just described are able to provide any significant protection to wood sited in exterior conditions for any length of time, a few weeks or maybe months at most.
...
One option would be to put no finish on at all. The charred wood surface will gradually go grey, there's no time hungry ongoing maintenance required requiring some commitment on your part and, being oak, the wood is naturally durable, i.e., it'll last for many years, maybe twenty or more, mostly ignored and exposed to the weather and UV light. Slainte.

I got through to Liberon support this morning and they suggested I can build up the sheen with 0000 steel wool over several layers but they cannot say how many. Do you have any experience or opinion on this?

I don't necessarily expect to keep the sheen forever - or the oak looking like that forever. I was more curious than anything if I can do it to use it later for indoor furniture (plus I really like it). I'm happy with the oak changing over time - a good deal of the lavender beds are in untreated oak.

We went with tung because:
a) the wood will be in contact (burried) with soild and I didn't want biocides leeching
b) I couldn't find any ground rated treatment (biocides or not) anyway
c) tung was supposed to be used in ground contact
d) tried a bit, liked the look and partially misread the instructions

Are you aiming for a shou sugi ban look? I have experimented with this myself and researched it a bit. I suspect to get a truly black look, you will need a much deeper char - the outside needs to be burned, not just coloured. Even then, I have never seen anyone achieve a long lasting gloss look by using oil.

There are loads of you tube vids on this, and most of them are from weekend wood warriors who are playing at it. Some people get it right - I recommend this video from Mr Chickadee. He does a proper burn:

I wasn't going for it. They have a proper burn on the sides and under where they will be in ground contact as that's what I read they used to do in the past to protect the wood. Apparently they used to char the wooden cobbles that were used to pave the streets of London so I figured it should hold for my two little ones for a few years.
I just burned them a bit on the top to hide the mold. I wasn't sure if giving it a deeper burn, they would still be suitable to walk on, but we (i.e. the missus) ended up liking this look better anyway.

That does look lovely! My experience is any exposed horizontal surface outdoors takes a pounding from the weather and sun. Any finish you apply will require regular maintenance to keep it looking how you want. I recently completed an oak gate and finished in Osmo UV Oil. I only did this for vanity as I wanted some nice photos of an oiled gate. However, It'll now be left to weather, and eventually go grey, and in 12months it will look worse than if I had never applied the UV oil in the first place.

Thank you! We originally wanted to treat this in Osmo decking oil + Osmo antislip oil. It would definitely have been easier than tung but are really unhappy with how it protected the oak decking. After a bit of reading it seemed to me that outdoor oak requires tung oil (plus a few other reasons I mentioned above) so we went with tung. I'm not fused about it looking the same over the years, just wanted to give it a nice head start if it makes sense.

 

[Sgian Dubh]

I got through to Liberon support this morning and they suggested I can build up the sheen with 0000 steel wool over several layers but they cannot say how many. Do you have any experience or opinion on this?

We went with tung because:
a) the wood will be in contact (burried) with soild and I didn't want biocides leeching
b) I couldn't find any ground rated treatment (biocides or not) anyway
c) tung was supposed to be used in ground contact

After a bit of reading it seemed to me that outdoor oak requires tung oil (plus a few other reasons I mentioned above) so we went with tung. I'm not fused about it looking the same over the years, just wanted to give it a nice head start if it makes sense.

In practice you can build up a bit of a sheen on top of many wood surfaces in tung oil with burnishing with anything from 0000 steel wool to even a soft cloth once you've applied somewhere between maybe three and perhaps five coats. You can add more coats if you want prior to buffing up. Even buffing won't give you more than a satin appearance, and that sheen soon dulls down in the best of circumstances, e.g., indoor furniture that sees little hard use, items such as primarily decorative hall tables and the like. The type of wood surface upon which this sheen building exercise is best achieved is generally a fine textured wood such as sycamore, maple or cherry. You're dealing with a naturally coarse textured oak, which you have made even coarser by charring, so building a sheen through burnishing is going to be more challenging ... actually, probably not very effectively really.

Your plan as I understand it, is for the piece to be located externally, and tung oil really confers little or no protective properties in such circumstances, i.e., against weather and UV light, and tung oil has no fungicidal or biocidal properties and therefore no appreciable protection for wood in ground contact. Whatever sheen you may be able to build up on visible parts of the wood will almost certainly deteriorate within a few days,and certainly within a few weeks, particularly on upward facing horizontal surfaces, and the oiled finish will generally deteriorate in appearance rapidly, within months. But, perhaps crucially for you, the appearance will be rather attractive in the first place, probably for a few weeks or maybe months, even if your initial enhanced sheen dulls appreciably in less time.

European oak and American white oak are both naturally durable wood species with the European stuff being somewhat the more durable of the two. Durable has a specific meaning in timber technology terms, referring to a wood species's ability to resist rot in ground contact - both those oak species are defined as 'durable', meaning an expected life expectancy of 20 - 25 years, and longer when used externally but away from ground contact. I can't tell where your reading led you to conclude tung oil had significant protective properties on wood located outdoors or in ground contact, but that really isn't the case. I'm aware that manufacturers of oil finishes frequently talk about feeding and protecting the wood in their marketing material, but in reality those claims are just that, marketing. Oils really don't penetrate deep into the wood below the surface no matter how much you put on, how much you thin it, nor how often you apply it. They generally penetrate up to a maximum of perhaps 0.5 - 1 mm when applied topically, i.e., brushed, wiped or sprayed on. There techniques for achieving deeper penetration, e.g., vacuum chambers, long term immersion of wood in oil, and so on, but I don't think these sort of techniques apply to your situation.

On a side note, to confirm something you have discovered, charring is definitely an old and well known technique for improving the durability of wood. Another historical example of charring for this purpose is a quite heavy burning of the ends of fence posts prior to burying them in the ground. Slainte.

 

[MikeG.]

.............After a bit of reading it seemed to me that outdoor oak requires tung oil ........

Well, given that none of the oils will last any time at all, there isn't much point in choosing one above any other (except as you point out, if there is any planting which could be affected). Chuck whatever you have to hand on it, take your photos, then say goodbye to it because it will be gone by the end of the winter.

 

[wood_i_rather]

In practice you can build up a bit of a sheen on top of many wood surfaces in tung oil with burnishing with anything from 0000 steel wool to even a soft cloth once you've applied somewhere between maybe three and perhaps five coats. You can add more coats if you want prior to buffing up. Even buffing won't give you more than a satin appearance, and that sheen soon dulls down in the best of circumstances, e.g., indoor furniture that sees little hard use, items such as primarily decorative hall tables and the like. The type of wood surface upon which this sheen building exercise is best achieved is generally a fine textured wood such as sycamore, maple or cherry. You're dealing with a naturally coarse textured oak, which you have made even coarser by charring, so building a sheen through burnishing is going to be more challenging ... actually, probably not very effectively really.

Your plan as I understand it, is for the piece to be located externally, and tung oil really confers little or no protective properties in such circumstances, i.e., against weather and UV light, and tung oil has no fungicidal or biocidal properties and therefore no appreciable protection for wood in ground contact. Whatever sheen you may be able to build up on visible parts of the wood will almost certainly deteriorate within a few days,and certainly within a few weeks, particularly on upward facing horizontal surfaces, and the oiled finish will generally deteriorate in appearance rapidly, within months. But, perhaps crucially for you, the appearance will be rather attractive in the first place, probably for a few weeks or maybe months, even if your initial enhanced sheen dulls appreciably in less time.

European oak and American white oak are both naturally durable wood species with the European stuff being somewhat the more durable of the two. Durable has a specific meaning in timber technology terms, referring to a wood species's ability to resist rot in ground contact - both those oak species are defined as 'durable', meaning an expected life expectancy of 20 - 25 years, and longer when used externally but away from ground contact. I can't tell where your reading led you to conclude tung oil had significant protective properties on wood located outdoors or in ground contact, but that really isn't the case. I'm aware that manufacturers of oil finishes frequently talk about feeding and protecting the wood in their marketing material, but in reality those claims are just that, marketing. Oils really don't penetrate deep into the wood below the surface no matter how much you put on, how much you thin it, nor how often you apply it. They generally penetrate up to a maximum of perhaps 0.5 - 1 mm when applied topically, i.e., brushed, wiped or sprayed on. There techniques for achieving deeper penetration, e.g., vacuum chambers, long term immersion of wood in oil, and so on, but I don't think these sort of techniques apply to your situation.

On a side note, to confirm something you have discovered, charring is definitely an old and well known technique for improving the durability of wood. Another historical example of charring for this purpose is a quite heavy burning of the ends of fence posts prior to burying them in the ground. Slainte.

Many thanks for the advice. Will give it a go with whatever oil I have now and see how long it lasts, but as I said not too bothered on that front.

As a side note, I found it referenced to it being used in ground contact here Tung Oil - Woodwork Details

 

[Sgian Dubh]

As a side note, I found it referenced to it being used in ground contact here Tung Oil - Woodwork Details

Hmm? The writer in the link is evidently well meaning, and a bit of research shows he's an enthusiastic amateur rather than a professional woodworker and/or wood finisher with years of practical experience and training to draw upon. Reading that link on tung oil he'd written did rather suggest he was repeating what he'd researched and/or read somewhere rather than sharing substantial first hand knowledge and practical experience of tung oil along with how it performs in service. Slainte.