Official Luthiers Forum!

Remember that Michael uses supplemental UV while Patrick does not. This makes a huge difference.... And it's how both of these guys can be "right" at the same time while using techniques that appear completely opposite and at odds with eachother.

The supplemental UV cures out the varnish way faster than its natural ambient curing rate would ever allow. You can put on a much thicker coat and it will cure hard - whereas using only natural curing - the same application would take weeks and still be a globby, mushy, puckered mess.

Probably the major difference is the amount of thinner used. With a UV cure - you want as little thinner as you can get away with. Only the minimum required to get your finish to brush and level. That way - you don't have to contend with waiting around for the thinner to evaporate so the finish can get around to curing. Wiping - you need enough thinner so it doesn't get sticky on your cloth and turn tacky while you are in the middle of applying it. Too much thinner leaves an ugly matte finish.

Brushing for a conventional ambient light cure takes the most thinner of all - as it has to brush nicely and build a thin enough coat to naturally cure. I have done this with Tru Oil and it generally takes me 20-40% thinner to get it to flow out properly and not leave brush marks or a thick, gloppy, runny, puckered finish. If I am brushing for a normal ambient cure (no supplemental UV) - Tru Oil is way too thick out of the bottle... But it does brush very nicely once it's thinned out enough.

So... There are 3 different application methods. Pick your poison. One thing though - don't mix and match. Don't wipe it on thick and gloppy in a cool, dark garage or basement and expect it to cure out right.

I've never used Tru-oil but have used plenty of Minwax Poly Oil on furniture. Can anyone having used both explain the difference?
And is Poly Oil suitable for guitars?

Thanks,

Jim

Yes. If you really want to keep it simple just use the wipe on technique. It takes much longer (waiting time) than my technique but virtually nothing in the way of equipment is required to apply the stuff. I'd still be tempted to take the woodwork to a pretty high grit if you want that very flat highly polished finish. It will reduce the number of coats required. Tru oil isn't my standard finish. It's shellac/French polishing because it seems to end up a touch harder. Even when I French polish I wipe on a base coat of Tru oil, just to pop the grain.

Michael,

Is your UV cabinet home made? Would you care to describe the unit that you are using? Thanks!

I'd like to know more about it too. Also, do you find that it has a big effect on certain wood colors that naturally change with aage and light exposure?

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Bryan Bear PMoMC

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It is home made. I bought an old single wardrobe from some charity outlet, the equivalent of $10 or $12. It's lined with kitchen foil with a few air vents that allow air circulation without allowing light out. It has just two BL350 tubes inside, I can't remember if they are 18" or 24". Ballast is mounted on the outside, on top of the cabinet (they get hot). I also use a baby bottle warmer on the inside to prevent the humidity dropping too low. Two tubes isn't considered very many but I've found it quite sufficient. Some people use 6 or 8 tubes. I primarily use it to tan wood but I've also dried many types of oil varnishes in it. The BL (of BL350) stands for Black light, 350 is the wavelength. These are the visible lights used by printers for drying inks. I think they are the same as the lights used in those insect zappers that you see in food stores. The whole thing may have cost me under $80, including lights and ballast. The ballast has to match the size of tubes that you are using.
With Tru oil I have to switch on the UV some 10 or 15 minutes after placing it in the cabinet. If I switch on too soon the stuff dries too rapidly and the Tru oil doesn't self level that well. Most oil varnishes do not act like that and I can switch on immediately. I also have a feeling that the UV cabinet hardens shellac finishes a little sooner than otherwise. That could have something to do with the UV but things are also a little warmer inside the cabinet, of course it could be a combination of both factors. You need to monitor the temperature and humidity inside the cabinet before placing any instrument in it, otherwise you are taking a risk.
I can also use it to dry oil finishes that have been directly applied to rosewood. I really have to blast it with UV though, 4 or 5 days 24 hours per day and it finally hardens.
It does change wood colour, sometimes dramatically dependent on how many days you leave it in there. I use it for spruce and maple, especially if I want an aged look. Maple is the one that I find it the most useful for.
Finally it can also be used for conditioning wood if your dehumidifier is having trouble dropping the humidity. In which case remove the baby bottle warmer and monitor the humidity inside the cabinet. A larger double wardrobe is probably better for that particular purpose though.

Great information! Thank you, Michael.

How long does it take to dry a coat of Tru-Oil before recoating?

Brushed coat? I can recoat after 2 hours. Wiped on coat probably 1 1/2 hours, perhaps a little less.

Jim,
I've been experimenting rubbing thinned poly on two guitars.
I thin it with mineral spirits.
I apply similar to tru oil, wipe on, wipe off.
What really has worked great is to apply a very thinned coat for the last one.
It flows out and leaves a very glossy even sheen.
I don't know how durable it is, but it looks great.
Dan

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Wah-wah-wah-wah
Wah

I want to say that I am impressed by Michael's results and I want to know more about this UV curing method. Seriously! This must be a great breakthrough and I am ready to learn with the rest of you!

Cool information about the UV cure unit. The BL350 laps sound like they could be put into any HW store florescent fixture, so it's not hard to imagine a simple plywood cabinet with a few lights in it to speed up curing finishes. I may have to build one of those.

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Blog on Making Stuff: http://www.McGlynnOnMaking.com

My tubes are longer than I thought - 3 ft. each.
There's nothing new about these UV cabinets, they are frequently used by many violin makers and they've been using them for at least a few decades. They tend to use old fashioned resin oil varnishes, frequently without added driers. They need the UV to get their varnishes to dry in a sensible time period, otherwise they could be waiting days for one coat to become touch dry.