Finishing Cocobolo

[btberlin]

Thanks. Epoxy is what I am leaning towards, considering the reply from tech support on the Target finishing board - i.e., that their finish system will bond well over epoxy. SB112 is actually designed apparently, as a boat hull sealer and I see it in quantities up to gallon on some of the boating supply sites. It is cheaper though, per ounce to purchase from one of the web luthier suppliers, even with shipping. So this is what i will start with on the cutoff pieces to see how it handles. I certainly would use the fillers to expand the resin and make sanding easier. But - this is the kind of experience information i was seeking, and I will start with it.

thanks again.
bert

[Kevin Sjostrand]

I did more scraping with a razor blade on the epoxy to level it then I did sanding...just sanded to knock off any tracks left from the scraping

Kevin

[B. Howard]

SB112 is fairly sensitive to mix ratio. It will blush easily. I use a digital scale to measure mine for mixing.
10 grams resin:4.4 grams hardener. Mix thoroughly for about 90 seconds then blend in the fumed silica. about a table spoon or so, enough to make it look like whipped cream. I apply it with a squeegee. Coco will need two, perhaps three coats.

[btberlin]

Thanks to Kevin and Brian for the advice regarding SB112 over cocobolo. These are very helpful pieces of advice to start with. And, they coincide with Jeff Weiss' advice (Owner of Target Coatings) for a base over which the Target materials will perform well. Since I like the EM6000 WB lacquer as a finish coat, this advice will serve me well.

As an aside, Brian, you might want to try a quart of EM6000 some time. It does not have the blue cast that you experienced in the early WB products on the market. It burns in rather nicely, I find, so that there are no witness marks during leveling, and for those of us that haven't invested in a 14-inch buffer, it does shine up very nicely leveled dry with the new 3M purple pro grade sandpaper 600 grit, followed by Abralon dry up to 4000, followed by McGuires applied by machine. Not quite as shiny as the Martin factory gloss, but, quite acceptable.

Even with dry sanding, the EM6000 sands to a nice white powder, which taps (or wipes with a microfiber detail cloth) right out of the pro grade sandpaper (which is apparently designed for sanding finishes). I believe it is rather susceptible to denatured alcohol, rather like shellac - so if the owner of the finished product uses his/her guitar as a resting place for a glass of hard liquor this would not be the right finish to use.

Bert

[B. Howard]

Bert, a few years ago I headed a green certification project for the company I was working for which was one of the larger and more exclusive high end builders in the region. We thought that switching to a water based finish system would be the short path to that end. During that time we ran out samples from some of the top coatings manufacturers. I even brought in the M.L.Campbell mobile coatings lab to do some side by side comparisons of coatings which included lacquer, conversion coatings, water born, and epoxy-urethanes. We also ran samples of Sherwin Williams and another lesser known brand but not target. While it would have made compliance a fairly easy task, every single designer and project coordinator could pick out the water born finishes quickly at a glance and none of us cared for the way the looked. They all lack "warmth" and to some degree clarity. And then there is the blue cast....as the chemists explained it to me, this could be mitigated to some degree but will never disappear totally. This has to do with the process where the esters are put into an aqueous solution. It involves a distillation process to remove the initial solvent (usually acetone) after the introduction of the glycol. This causes a further polymerization of the resins and the shift in color and clarity. If I ever do move away from the nitro in the guitar finishing businesses I will most likely go with an amino-alkyd conversion varnish. This is because I already have all the equipment and expertise to do so.

This is not to say the WB finishes do not have their advantages. They most surely do. Ease of use and clean up are at the top of that list. But they are not completely solvent free, there are a lot of glycol-ethers in them. I have been told that certain WB coatings have already been reformulated to drop the amount of solvents in them to meet new thresholds of 350 gpl. They also pose a major health risk when atomized, inhalation of the actual spray is very bad due to the cross linking compounds used to make the resin knit into a coating from an aqueous base. So please use a respirator when using them.

[btberlin]

I believe a few years in the more recent development of WB's may have led to an improvement in the clarity and color problems. I can't say for for sure as I have no way of objectively testing, but it would be interesting to see if any of the current woodworking mags, like Fine Woodworking, have done objective testing again. I can say that subjectively,over Sitka, the Target EM6000 doesn't seem to have the same tendency towards blueness, although i can't be certain. It looks rather like it has been sprayed with blond shellac, perhaps a tad warmer. The other interesting part of EM6000 is that it does burn-in like a nitro lacquer (perhaps not "like" but "in a similar way"), so as to eliminate witness lines. Jeff Weiss has also said that the burn-in can be improved in long-cured EM6000 by wiping the cured surface down with 50% denatured alcohol. That said, i suspect Target has hit on the chemistry of a WB lacquer that has some of the good features of Nitro.

But now, to another point. I understand this forum to be read by luthiers of all stripes, capabilities, and levels. That, to me, means that we probably should not imply that one particular finish type is the only way to go. I happen to favor WB, and have used WB on every project i've done in the past decade or more (since they appeared, and certainly since Fine Woodworking did their testing). From my perspective, it's a safe way to get the finish results i want, using the equipment i already have, and which doesn't put me at risk of having explosive vapors. So, while you have the resources and equipment to shoot nitro, i suspect there are others in the forum, who, like me, will benefit from trying out some of the easier-cheaper ways of getting to the end-result - a clear, attractive, shiny finish. I am still using a compressor a friend gave me in the 90's when the valves in one cylinder broke, and he hadn't the patience to find a source of replacement parts, remove the head, and repair it. Along with that, a beginner can actually find a decent touch-up gun at Harbor Fright - their hvlp touch up gun looks and performs like similar guns in the $100 and up category, for about $30 on sale. When adjusted properly it makes a nice fan, and atomizes WB nicely, leaving a finish comparable to my Asturo hvlp gun. So, someone starting out with spraying can probably find a compressor on Craig's list, and a gun at HF (along with the requisite air dryers, water separators, pressure regulators, and cleaning brushes), and get started spraying without breaking the bank. When i am testing new materials, i use cutoffs from the project, or a nearby lumber yard, and go through the finishing steps i would use on a guitar body. Then I evaluate. In the case of the Target coatings, I chose to use the entire line of relevant products, from vinyl sealer, through the grain/pore filler, stain, and finish coat. From my perspective, compatibility is important, and sticking with one manufacturer means that i can get more definitive advice when needed from tech support. So - while we've gone off topic, we are on a related topic I think, and for anyone reading this who has been thinking about spraying finish, it is very do-able in your garage without spending a fortune. And, remember, as Brian indicated, always wear a decent respirator rated for vapors of the material you are spraying. The half-mask types run about $35 on amazon and at the big-box stores. Water based doesn't mean that water is the ONLY solvent in WB finishes, and the others can be really nasty to inhale. The resin(s) probably ain't too good for you either.

Bert

[johnnparchem]

Interesting discussion. I use em6000 almost exclusively over zpoxy. I actually like the slight amber tint of zpoxy as it helps with WB finish color. It is possible to get a decent looking finish and em6000 is relatively forgiving, but I agree it still does not look like nitro. I have also found it is possible to get a noticeable blue tint if the coats are too thick. On my guitars I am finding about 15 three mil coats no sanding till they are all done produces a good finish. To be successful before even starting to spray the surface should be dead level coming out of the prep sanding and pore fill. Here is a picture of a refinish I just completed with EM6000

[Kevin Sjostrand]

That is georgous JOhn. I may have to try this lacquer some day as the nitro is going to be hard to get sooner than later here in California.

Kevin