Applying Nitrocellulose Lacquer

August 16, 2011

( I copied this from my blog about the construction of a 12 string guitar because I think it describes the process pretty well.)

I use nitrocellulose lacquer as the finish for most of the instruments I build.  Each of the many acceptable types of instrument finishes has its strengths and weaknesses.  I have worked with  lacquer for many years and have a pretty good understanding of it.  I have developed an approach to working with it that gives me consistent results.  It takes 4 to 6 weeks for me to get the finish on an instrument.

  People often ask me how many coats of lacquer I apply and I am never really sure what they are hoping to hear in response.  An easy answer to the question would be that there is only one coat, since subsequent layers melt into and fuse with previous  layers when they are sprayed.  I do have an approximate count of the number of times I point my spray gun at an instrument, so I could tell people that there are 15 to 20 coats of lacquer.  However, there is no consistent definition of what a “coat”  represents as far as a quantity of lacquer.  Every person who sprays can apply a different amount.  There are three ways to vary how much lacquer is applied with each pass of the gun: first, one can increase or decrease the volume of lacquer that comes out of the gun by adjusting a needle valve; second, by changing the speed at which the gun is passed across the surface, different amounts of finish material will be deposited on the surface; and third, by changing the thickness (viscosity) of the lacquer, more or less will remain on the surface after the volatile solvents evaporate.  So my concern with telling people a specific number is that they might think it is either too many or too few coats, even though we aren’t necessarily thinking of the same amount of lacquer.  I usually end up telling people that I don’t know how many coats are on the guitar and that I use just enough lacquer to seal all of the wood pores and to allow me to sand the finish perfectly flat and buff it to a high shine, which is true.

Here are a few action shots of the spraying process.  In addition to the particulate respirator, the other very important safety consideration, which is not visible, is my use of an explosion-proof exhaust fan.  Nitrocellulose is volatile and without this type of fan I would be at great risk.

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