I just read a thread in the general discussion about someone who used this product and is now swearing off building guitars. I also had a very bad experience with this stuff, and wanted to get a discussion going, while also countering some of the bizarrely glowing praise I've seen online.
The main benefit of lacquer, as I see it, is that you can apply it very thinly and build it up in layers that melt into each other to create a mirror-like finish that is thin and allows the wood to resonate. I'm not one of those people who thinks any of these finishes "breathe" or whatever, but there is certainly a benefit to avoiding a super thick, plasticky finish.
"I can't believe it's not lacquer" will not build up in layers that melt into each other. If you want to apply more than one layer, you need to make each layer absolutely flat and perfectly polished before applying the next layer, otherwise you can see shiny spots and flat spots within the finish. In other words, you have to do a full "final" sand and polish with each layer of finish, which is exhausting and time consuming.
Of course, with the first couple of layers, if you're applying thinly, the risk of sand-through is huge if you have to perfectly level and polish the finish. Otherwise the only option is to really gloop on the finish for the first layer (or maybe the only layer?) to avoid sanding through. Going for a very thick first layer is also an option to avoid the shiny and flat spots in the finish that remain between layers, but the final result is a guitar with a very thick, plasticky finish.
You have to grain-fill open pored woods with this stuff, even if you want kind of a "raw" wood look. I don't ususally grain fill even woods like mahogany or ash, because I like the look of the raw wood. I prefer to instead build up many layers of lacquer or oil, which smooths out a lot of the grain, and then it shrinks into the grain as it ages, which I think looks amazing. However, even if you want that look, you should not use this product on an open-pore wood. Why? This stuff cures in sunlight, and the product that seeps into the pores will never cure, because it will never be exposed to sunlight. I used this stuff on mahogany and left it in the sunlight for about 10 minutes, rotating a few times to make sure I hit it from every conceivable angle. Afterward, when I saw how bad the finish looked (the aforementioned flat spots and shiny spots visible between layers), I sanded it all off and set the guitar down while I worked on another project for a few weeks.
When I came back to it, there were little wet spots all over the mahogany, and the end grain was pretty much soaking wet. It took me some time to figure out what was going on, but I realized the un-cured product was seeping out. I recured the guitar again in the sunlight, but when I sanded again, the same wet spots showed up again. I did this about five times, and each time the little wet spots showed up. Now, if you cure the top coat I'm sure you won't see wet spots and you won't have the product seeping out, but what you will have is wood grain that is basically perpetually wet in the pores of the wood. How will that instrument resonate, wet wood fibers and all?
Let's see, what else? The instructions are pretty lacking online at this point, and of course the instructions on the bottle are only marginally helpful.
Oh, one more thing. This stuff gives off a lot of heat as it cures - if you put some on your hand and put your hand in the sun it will burn like crazy. I don't know if it gets hot enough to compromise glue joints, but it definitely gets hot enough to make me wary about putting it on wood that I want to keep at a semi-constant temperature for stability reasons.
The main promise of this stuff is that it's similar to lacquer (it's not, at all), and it saves time because it cures in the sun in a matter of minutes. I would argue that it is WAY more effort to use due to the insane amount of sanding and polishing between coats, not to mention the issue of the product not curing when it seeps into the wood, and the thick, plasticky finish you end up with if you do it all with one coat.
The main benefit of lacquer, as I see it, is that you can apply it very thinly and build it up in layers that melt into each other to create a mirror-like finish that is thin and allows the wood to resonate. I'm not one of those people who thinks any of these finishes "breathe" or whatever, but there is certainly a benefit to avoiding a super thick, plasticky finish.
"I can't believe it's not lacquer" will not build up in layers that melt into each other. If you want to apply more than one layer, you need to make each layer absolutely flat and perfectly polished before applying the next layer, otherwise you can see shiny spots and flat spots within the finish. In other words, you have to do a full "final" sand and polish with each layer of finish, which is exhausting and time consuming.
Of course, with the first couple of layers, if you're applying thinly, the risk of sand-through is huge if you have to perfectly level and polish the finish. Otherwise the only option is to really gloop on the finish for the first layer (or maybe the only layer?) to avoid sanding through. Going for a very thick first layer is also an option to avoid the shiny and flat spots in the finish that remain between layers, but the final result is a guitar with a very thick, plasticky finish.
You have to grain-fill open pored woods with this stuff, even if you want kind of a "raw" wood look. I don't ususally grain fill even woods like mahogany or ash, because I like the look of the raw wood. I prefer to instead build up many layers of lacquer or oil, which smooths out a lot of the grain, and then it shrinks into the grain as it ages, which I think looks amazing. However, even if you want that look, you should not use this product on an open-pore wood. Why? This stuff cures in sunlight, and the product that seeps into the pores will never cure, because it will never be exposed to sunlight. I used this stuff on mahogany and left it in the sunlight for about 10 minutes, rotating a few times to make sure I hit it from every conceivable angle. Afterward, when I saw how bad the finish looked (the aforementioned flat spots and shiny spots visible between layers), I sanded it all off and set the guitar down while I worked on another project for a few weeks.
When I came back to it, there were little wet spots all over the mahogany, and the end grain was pretty much soaking wet. It took me some time to figure out what was going on, but I realized the un-cured product was seeping out. I recured the guitar again in the sunlight, but when I sanded again, the same wet spots showed up again. I did this about five times, and each time the little wet spots showed up. Now, if you cure the top coat I'm sure you won't see wet spots and you won't have the product seeping out, but what you will have is wood grain that is basically perpetually wet in the pores of the wood. How will that instrument resonate, wet wood fibers and all?
Let's see, what else? The instructions are pretty lacking online at this point, and of course the instructions on the bottle are only marginally helpful.
Oh, one more thing. This stuff gives off a lot of heat as it cures - if you put some on your hand and put your hand in the sun it will burn like crazy. I don't know if it gets hot enough to compromise glue joints, but it definitely gets hot enough to make me wary about putting it on wood that I want to keep at a semi-constant temperature for stability reasons.
The main promise of this stuff is that it's similar to lacquer (it's not, at all), and it saves time because it cures in the sun in a matter of minutes. I would argue that it is WAY more effort to use due to the insane amount of sanding and polishing between coats, not to mention the issue of the product not curing when it seeps into the wood, and the thick, plasticky finish you end up with if you do it all with one coat.