I'm starting to think that my problems polishing lacquer are caused by not enough cure time. How long do you let lacquer cure?
Recently I had a project sit for two months between laying down the lacquer and polishing. I had such a different experience polishing this project. Obviously I can't have customers waiting two months for finishing. So what is your minimum cure time?
2 months for violin varnish is sometimes just a starting point...
What lacquer? Keep in mind that adding pigments and other substances can radically alter the drying properties, but for nitro 2 months makes me think that something is not right with the lacquer, or you have added something that is interfering with the curing process.
Have you considered a UV booth?
Not a satisfactory answer, but no amount of time is too much—I would wait 'til the last day before you absolutely have to set the instrument up in preparation of shipping it out.
Hard question to answer without knowing what lacquer you are using, what additives may have be in the mix, the preparation, and the atmospheric conditions under which the spraying and drying are done.
I've always been under the impression that lacquers technically never "cure" as evidenced by what happens were you to spill alcohol on a lacquered finish. Am I wrong?
A typical example. Mohawk pre-catalyzed clear gloss lacquer from a rattle can. Lacquer is laid down on an ebony peghead. How soon can I polish it?
I'm no luthier, so I don't know, but a banjo-building friend of mine likes Cardinal LuthierLac, available from Luthiers Mercantile. Ready-to-spray from the can and ready-to-buff in 7 days. Or so it's claimed.
You could always spray a test board to see if it's true.
I like to wait at least a month but have wet sand and buffed in two weeks. it will sand a d buff much better the longer you wait
Also I like to thin mine 50 percent with a high grade thinner.
I've never used rattle lacquer but would think it would be the same except the thinning.
This is just a theory, but in my experience, it depends on how much time is left between coats. When a new coat is applied before the previous coat has fully dried, vapors from the previous coat become trapped and take longer to escape and evaporate making it stay soft longer. Coats that have plenty of dry time in-between will reach full cure in less time after that final coat.
In working with my father as he made Williamsburg reproduction furniture and clocks, I know the finishing time varied quite a bit here with our Pennsylvania humidity changes. He was not under the gun with regard to the delivery time to customers. You got it when it was done. I recall him in the final coat rubbing the pieces with jeweler's rouge which couldn't be done if the finish wasn't hard enough. My memory fails me in this regard, but I believe the finishing process was probably as long as the building process on some pieces, and both were shorter than the time wood would sit and acclimate prior to work beginning. All work and finish curing was done at a constant room temperature with humidity control having to be added. I didn't have the patience he had in this regard. He passed away in 1986. I really wish he was still around. I have a million questions and he would have made fine instruments. My pre-raising kids and pre-banjo era.
My experience with wooden cabinets is to use an alcohol based dye, and top coats.
My personal kitchen cabinets are 3 tone sunburst, topped with shellac.
Around sinks I top coat with a poly.
I have heard that some luthiers top coat with shellac but I am not positive about that.
Any chance the problem is the ebony and not the lacquer? I have had some ebony/rosewood that was just about impossible to hold any finish. It was just too oily.
I also think that your location would make your lacquer dry faster than just about anywhere else in the country.
Originally posted by maneckep
Any chance the problem is the ebony and not the lacquer? I have had some ebony/rosewood that was just about impossible to hold any finish.
I've had this happen with Cocobolo. A wash coat of shellac did the trick.
My finish of choice is not lacquer; but, since the time is available to me, a few reference books were consulted.
Jeff Jewett, in his book "Finishing," recommends letting lacquer cure at least a week before rubbing it out. He also adds that if the finish loads up your sandpaper it's not dry enough.
In another older book, "Finishing" by Jeff Engler, the author has a chart showing lacquer to be hard in one day.
Some research on the Internet also yielded differing results, but most were within one day to one week.
My finish of choice is shellac. In researching an answer to your question, it was noted that lacquer cures quicker than shellac. In my experience shellac can be rubbed out in a day, but two or three days is much better.
If I were going to experiment with lacquer, I'd start with a two day cure time and use a sandpaper loading test to see whether a longer or shorter cure time would be appropriate.
'Bacon Banjo Quintette' 4 hrs
'Banjo Neck' 7 hrs
'FINGERNAIL' 7 hrs
'Hoosier Old Time' 7 hrs