Rick Turner
Well-known member
There's a lot of chatter about "UV Finishes" here with little apparent understanding of what they are.
"UV" is not in and of itself a finish. "UV"...Ultra Violet light...is a means of curing modern polyurethane and polyester finishes, and is used instead of the more conventional addition of a catalyst to the base resins. The main advantage of UV is the speed of cure...it can be under a minute from out of the spray gun wet to cured when the coating is exposed to the right wavelength and intensity of UV light. The secondary advantage is that you don't have to mix resin and catalyst together, and in fact, the urethane or polyester can be pumped from a drum and the gun can be left unattended overnight...the finish won't cure in the liquid lines or gun.
As a uke owner, you cannot tell the difference between catalyst and UV cured finishes. Catalyst cured polyester MAY be a tiny bit harder than the same material UV cured according to guitar maker Tom Anderson. In fact, the same exact basic resin formulas can be cured either with a catalyst (MEKP in the case of polyester, a more complicated formula for urethanes) or with the addition of a UV cure initiator (made by CIBA Chemicals and others...) and then exposed to UV. Tom, in fact, does some of his finishing as a "dual cure"...he adds MEKP to the UV initiated polyester, does a quick UV cure, and then has the additional harness of a 24 to 48 hour catalyst cure.
Bob Taylor advised me not to bother with UV curing finishes unless I was hitting about 100 instruments a month. Finish cure is not a real bottleneck under that number. It's razzle-dazzle; it's a great science fair project, but it's not a money maker unless you're doing major production. Frankly, spraying five instruments a day isn't really a big deal, and with the cat cured stuff, you can go start to cured top coat in five days...so you've got maybe 25 instruments hanging in various states of drying and cure at any given moment. Not a big deal.
There are UV and catalyst curing polyurethanes and polyesters, and because each has its advantages and disadvantages as materials, they can also be used together. I, for instance, use cat-cured urethane sealers under cat-cured polyester build and top coats, and I sometimes do sunbursts, translucent, and opaque colors with cat-cured urethanes between polyester build coats and polyester top coats.
And some of us use nitro lacquer top coats over polyester fill and build coats. This is quick and helps to avoid long term finish shrinkage into the pores of the wood. Note that UV is of no use in curing nitrocellulose lacquer...as my friends at SCGC expensively learned...
To make things even more complicated, there are UV curing polyester pore fillers that can be used over sealer wash coats and under just about anything. The disadvantage is that you must isolate polyester from Western red cedar or any rosewoods as the oils in the wood inhibit the cure of the polyester. Also, sometimes the UV light will not penetrate down into the pores, and you wind up with polyester jelly with a cured finish on top.
UV cured urethanes and polyesters are available in gloss or various degrees of satin sheen.
I get my urethane isolater/sealer and my polyester build and top coat materials from Simtec. WLS is a great supplier of urethane colors.
So, to wrap it up here...UV is simply a method of curing modern finishes; it is not a finish unto itself. I've seen a lot of luthiers and small manufactures be seduced into the UV cure thing...but given the cost of setting up for it, I can hardly see how it's worth doing unless one is building a whole lot of instruments. The cured finish is no better than that done with a catalyst.
"UV" is not in and of itself a finish. "UV"...Ultra Violet light...is a means of curing modern polyurethane and polyester finishes, and is used instead of the more conventional addition of a catalyst to the base resins. The main advantage of UV is the speed of cure...it can be under a minute from out of the spray gun wet to cured when the coating is exposed to the right wavelength and intensity of UV light. The secondary advantage is that you don't have to mix resin and catalyst together, and in fact, the urethane or polyester can be pumped from a drum and the gun can be left unattended overnight...the finish won't cure in the liquid lines or gun.
As a uke owner, you cannot tell the difference between catalyst and UV cured finishes. Catalyst cured polyester MAY be a tiny bit harder than the same material UV cured according to guitar maker Tom Anderson. In fact, the same exact basic resin formulas can be cured either with a catalyst (MEKP in the case of polyester, a more complicated formula for urethanes) or with the addition of a UV cure initiator (made by CIBA Chemicals and others...) and then exposed to UV. Tom, in fact, does some of his finishing as a "dual cure"...he adds MEKP to the UV initiated polyester, does a quick UV cure, and then has the additional harness of a 24 to 48 hour catalyst cure.
Bob Taylor advised me not to bother with UV curing finishes unless I was hitting about 100 instruments a month. Finish cure is not a real bottleneck under that number. It's razzle-dazzle; it's a great science fair project, but it's not a money maker unless you're doing major production. Frankly, spraying five instruments a day isn't really a big deal, and with the cat cured stuff, you can go start to cured top coat in five days...so you've got maybe 25 instruments hanging in various states of drying and cure at any given moment. Not a big deal.
There are UV and catalyst curing polyurethanes and polyesters, and because each has its advantages and disadvantages as materials, they can also be used together. I, for instance, use cat-cured urethane sealers under cat-cured polyester build and top coats, and I sometimes do sunbursts, translucent, and opaque colors with cat-cured urethanes between polyester build coats and polyester top coats.
And some of us use nitro lacquer top coats over polyester fill and build coats. This is quick and helps to avoid long term finish shrinkage into the pores of the wood. Note that UV is of no use in curing nitrocellulose lacquer...as my friends at SCGC expensively learned...
To make things even more complicated, there are UV curing polyester pore fillers that can be used over sealer wash coats and under just about anything. The disadvantage is that you must isolate polyester from Western red cedar or any rosewoods as the oils in the wood inhibit the cure of the polyester. Also, sometimes the UV light will not penetrate down into the pores, and you wind up with polyester jelly with a cured finish on top.
UV cured urethanes and polyesters are available in gloss or various degrees of satin sheen.
I get my urethane isolater/sealer and my polyester build and top coat materials from Simtec. WLS is a great supplier of urethane colors.
So, to wrap it up here...UV is simply a method of curing modern finishes; it is not a finish unto itself. I've seen a lot of luthiers and small manufactures be seduced into the UV cure thing...but given the cost of setting up for it, I can hardly see how it's worth doing unless one is building a whole lot of instruments. The cured finish is no better than that done with a catalyst.