Moderators: Random Orbital Bob, nev, CHJ, Noel, Charley

 Reply
By DanB
#1330209
Over the past approx four months I've been slowly designing and building myself a replacement telescope tripod, with extending legs formed from planed Oak battens. This is easily the most ambitious wood working project I've attempted, especially in terms of my quality goals. I have been learning a lot along the way, and fortunately thus far everything has largely worked out as expected. I've got the stage where I'm thinking about how to best finish the wood, and there are so many possible options with pros and cons to consider, that I'm struggling to come to a good decision.

The majority of usage of the tripod will be at night time in dry conditions, but there are evenings when there is heavy dew, or even frost, which settles on my current steel tripod. So a water resistant/repellent finish looks like a must have, but it is not likely to have prolonged heavy exposure to water/rain like outdoor furniture would (famous last words). There will be some day time usage for solar observing, but not for more than a few hours a month on average, so UV protection is nice but doesn't look critical. In general I'd like to stay close to the natural pale colour of the oak, with a matt finish.

Does anyone have recommendations for a finishing approach that is suitable for this application with oak ? Most accounts I've read of wooden tripod construction have finished with boiled linseed oil, tung oil & similar, sometimes with a wax top coat, or alternatively a solvent based polyurethane varnish. Are any water based varnishes going to be a workable option, or is an oil based finish or solvent based varnish the most sensible route here ? If the latter, then I'll have to delay until I can travel to use my father's workshop, since my working space at home is the back garden during fine weather spells only!
User avatar
By MikeG.
#1330216
Avoid oil and wax if the thing is going to get wet. I suggest you use a wiping varnish because brushing on orthodox varnish can produce a nasty looking thick and uneven coat. You thin an oil-based varnish down 50/50 with white spirit, slap it on any old how, leave it for 5 or 10 minutes, then wipe it off again. Leave for 24 hours and repeat, and end up with 5 or 6 coats. One of the great advantages is that your workshop doesn't have to be as clean as a laboratory.
User avatar
By Jacob
#1330227
Raw linseed oil is easiest - brushed on thin and excess wiped off after being left to soak for a bit. Do it several times at first, with a few weeks between . It's also very water resistant in the short term and would suit your usage as described. Colour darkens with age and sunlight, with or without a finish.
User avatar
By ED65
#1330319
DanB wrote:In general I'd like to stay close to the natural pale colour of the oak, with a matt finish.

Both of these would are potential problems for protection, and for durability. Gloss finishes are more protective than matt (and matt finishes are subject to buffing effects where they tend to easily get glossier along arrises and other high-wear zones, which to my mind somewhat defeats the purpose of them in the first place).

DanB wrote:Most accounts I've read of wooden tripod construction have finished with boiled linseed oil, tung oil & similar, sometimes with a wax top coat, or alternatively a solvent based polyurethane varnish.

Of those there's only one that would be anything like what you'd think of as waterproof (potentially, resistance to water is greatly dependent on coat thickness) and that's the last.

Linseed oils are about as waterproof as a paper bag. Do a test, you can easily confirm this for yourself, water goes right through a thin oil finish. You can't get good protection from oil unless you apply multiple coats over a long period. With linseed this is many, many coats. If you started now and kept at it you might be safe using it in July. Maybe. And it doesn't meet your criterion for leaving the wood light, in fact it will do more to change the colour than any other clear finish.

DanB wrote:Are any water based varnishes going to be a workable option

If you could find a good one, yes. They're generally much better than they once were and in tests some appear to be the match of oil-based varnishes, which have long had the reputation for being far superior. But how do you find a suitable one, that's the question?

The best thin-film protection you could give the wood is using a penetrating epoxy or CPES. But epoxies are sensitive to ultraviolet and generally need to be protected by something on top that shields it from UV. In a marine environment this would typically be a spar varnish (and many coats of it!) which you will not like look of I promise :lol:

As this is oak, there's the possibility of leaving it bare. Oak will do just fine without any finish on it, although it will accrue grime and marks it's not prone to rot. But from a stability standpoint you'd need to be confident the wood chosen was stable.
By DanB
#1330834
MikeG. wrote:Avoid oil and wax if the thing is going to get wet. I suggest you use a wiping varnish because brushing on orthodox varnish can produce a nasty looking thick and uneven coat. You thin an oil-based varnish down 50/50 with white spirit, slap it on any old how, leave it for 5 or 10 minutes, then wipe it off again. Leave for 24 hours and repeat, and end up with 5 or 6 coats. One of the great advantages is that your workshop doesn't have to be as clean as a laboratory.


Thanks for the wiping varnish suggestion, not having to worry about a spotless clean workshop is definitely a plus point.
By DanB
#1330839
ED65 wrote: Gloss finishes are more protective than matt (and matt finishes are subject to buffing effects where they tend to easily get glossier along arrises and other high-wear zones, which to my mind somewhat defeats the purpose of them in the first place).


I'll bear that in mind, as I'm willing to consider non-matt finish.

ED65 wrote: You can't get good protection from oil unless you apply multiple coats over a long period. With linseed this is many, many coats. If you started now and kept at it you might be safe using it in July. Maybe.


Hah, I think I can eliminate oiling from the likely options then, as time is precious !

ED65 wrote:
DanB wrote:Are any water based varnishes going to be a workable option

If you could find a good one, yes. They're generally much better than they once were and in tests some appear to be the match of oil-based varnishes, which have long had the reputation for being far superior. But how do you find a suitable one, that's the question?


I did an experiment with water based Polyvine Decorators Varnish, since I have a 1/2 finished tub from an unrelated toy house project & it was surprisingly labelled as both interior/exterior varnish. On an oak off-cut, after three coats it did offer reasonable water resistance, with the drops staying on the surface and sliding off without wetting the wood noticeably.

On contacting them for more info on its suitability though, their response was that they recommend against any of their varnish products in an exterior Oak scenario; Oil is the only thing that they could recommend. I get the impression though, when manufacturers consider exterior usage, they're thinking about situations where the wood is outside exposed 24x365 in all weather conditions. This is not going to be anything like the kind of exposure my tripod will get during usage though.

ED65 wrote:As this is oak, there's the possibility of leaving it bare. Oak will do just fine without any finish on it, although it will accrue grime and marks it's not prone to rot. But from a stability standpoint you'd need to be confident the wood chosen was stable.


I think I'll probably leave it bare for a while, and do some tests on off cuts to determine what suits it best.

Thanks to everyone above for the suggestions so far.
User avatar
By ED65
#1330904
DanB wrote:Thanks for the wiping varnish suggestion, not having to worry about a spotless clean workshop is definitely a plus point.

Yes! One of the (numerous) advantages of wiping varnish on instead of using it straight from the tin. Not all upside though, it does take many more applications to build up a full varnish coat – perhaps seven or more versus three full-strength coats brushed or rollered on.

DanB wrote:I did an experiment with water based Polyvine Decorators Varnish, since I have a 1/2 finished tub from an unrelated toy house project & it was surprisingly labelled as both interior/exterior varnish. On an oak off-cut, after three coats it did offer reasonable water resistance, with the drops staying on the surface and sliding off without wetting the wood noticeably.

=D> Yeah this is the minimum to look for. Really top-level performance, which is what I strive for when I varnish anything critical like a tabletop or a windowsill in a bathroom, is that you could leave the water on the surface and just let it evaporate. That's functionally waterproof, even though interior varnishes aren't waterproof per se.

DanB wrote:On contacting them for more info on its suitability though, their response was that they recommend against any of their varnish products in an exterior Oak scenario; Oil is the only thing that they could recommend. I get the impression though, when manufacturers consider exterior usage, they're thinking about situations where the wood is outside exposed 24x365 in all weather conditions.

I think you're right there.