Hammered Dulcimer design, construction, and unrelated stuff

Sunday, December 23, 2012

Spraying Shellac Revisited

I have been spraying shellac in production finishing of our hammered dulcimers for a year now, and have come up with a few more tricks, so thought I'd update.  Read the former post on the same topic, this is additional material to that.

I have found that shellac sprays best if it is mixed at an EXACT one pound cut.  This is pretty easy to do.  I have a jar that I dissolve the flakes in that is something less than one gallon, so just dump the flakes in, fill with alcohol, and stir several times the first day.  If I stir well a couple times within the first hour, the flakes will all be dissolved by the next day.  Then I filter the mix into a gallon jug, and top off with alcohol to get the right mix.  This is probably a little stronger than a one pound cut, but works best for me.

Jugs:  glass is best.  Milk jugs work, but are thin, and the shellac can actually find a weak spot, and eat through, and leak.  But you won't lose much, because the shellac dries, and is self healing.  I found a much heavier plastic jug that vinegar came in, and it has been working very well.

Since I had sprayed lacquer for so long, it took me quite a while to get the feel for the shellac.  I was putting it on too heavy.  So, one pound cut, spray light, and move fast.  Shellac goes on different than lacquer, it does not need to wet and flow out, so you wind up moving much faster than you'd think.  I am using about half the material I was, and getting a much better finish.  The surface may look a little pebbly, but give it a minute, and it will settle down, and gloss.  Go especially light on the first couple coats, which are your seal coats.  Much less grain raising that way.

Color:  I have gone to using just the Blond flakes that I still get from shellcshack.com.  They give just a little warm glow to the finish.  I no longer mix colors, but this is still a good trick for special finishes.  But production finishing, just the Blond.

Gun cleaning:  I clean after each time I spray, never leaving shellac sitting in the gun.  By cleaning, I mean, pour the remaining material back in the jug.  Put a little straight alcohol in the gun, shake it to get the alcohol all through the cup, then spray a little of the alcohol.  Pour the remaining alcohol into a separate container that I label "Gun Rinse".  Then pour a little more fresh alcohol in the cup, shake, then spray.  You can let the gun sit as long as you like now.  When getting ready to spray again, pour the alcohol in the cup into the gun rinse can.  The gun rinse alcohol can be used in mixing up the next batch of flakes, so you don't waste any of it.  It is a good idea to take your gun apart a couple times a year, and soak and thoroughly clean all the parts.

Shellac is harder, and more durable than lacquer.  I have switched to it completely.  I don't spray lacquer at all now.  So much better!  It is also more beautiful than lacquer.  I still use the Minwax Wipe On Poly as a sealer, as described in the former post.  It works great, and helps the shellac build faster.  I just wipe it on straight, and let sit overnight.  Then scuff lightly with 220 grit paper on a sanding block. For scuffing in between coats of shellac, I have found 400 grit best, wrap 1/4 sheet around a rubber sanding block, and move your hand slowly and with very light pressure, basically just the weight of the block and your hand.  Don't press down.  If you do it right, the paper won't load at all, but if you move your hand too fast, or press down too much you will generate heat, and the dust will load the paper.  I have a piece of carpet on my sanding bench, so just wipe the paper on that to get the dust off.  With a smooth couple of seal coats, I don't need to do much sanding, just go over it lightly to get the dust motes off.  If there is a rough spot, I can do more sanding there to get it smooth.

Final polish:  With the much better job of laying the finish on that I have developed, I don't need to rub out.  The gloss is there, just like I want.  So for the top of the dulcimer, I just pass over it VERY lightly with a worn out piece of 400 grit paper to remove any dust motes.  You can't see that I have done this, and it doesn't affect the gloss at all.  For the back and sides, I still love the feel and look of wax, so I sand a little better, then wax.  I probably wouldn't need to wax, just go over the whole dulcimer lightly with the worn out 400 grit.  I just really like the feel of the wax.  These are by far the best finishes I have done in over 20 years.

I have gotten good enough with my move fast, spray light technique that I have been able to drop the use of the bed of nails on the turntable, and go back to suspending the hammered dulcimer bodies from a string hanging from the ceiling of my spray room.  I worked this way for 20 years spraying lacquer, and it is much faster.  I can spray all around the body at once.  I do six at a time.  To do the whole finish on six dulcimer bodies used to require a little less than a gallon of lacquer mix.  Two quarts of sealer mix, and 2 quarts of semigloss mix.  With my move fast, spray light technique, I am down to just over a quart of 1 pound cut shellac to do the same job, and the finish is better.  So about 1/3 of the material, and shellac works out to be cheaper than lacquer.

So; shellac is harder, more durable, and better looking than lacquer.  It takes a little longer to apply, but the results are worth it.  I am using a lot less material than I would lacquer, and I believe this has translated into cheaper.  Shellac is safer, I don't need to keep 5 gallon buckets of hazardous materials around.  It is safer for the environment, safer for me.  It is also safer for customers since there are no chemical sensitivity issues.  It is better for the economy since I am not supporting a large chemical company, just small businesses like shellacshack.com, and the guys in India that produce the flakes.  It is a win/win/win/win situation.  What isn't to like here?

In going over these posts I realize I have left out something big.  Spraying shellac can be dangerous.  An aerosol mixture of alcohol is explosive.  Don't try it in your basement.  You either need to be outside in the open air, or you need explosion proof facilities inside.  There are two types: A spray booth, and a spray room.  A spray booth is a 3 sided box with a very large explosion proof exhaust fan in the back, and over spray arrestors to filter the air before it goes through the fan.  Large spray booths are where body shops paint your car, and they require a LOT of air to keep any of the aerosol spray mix from escaping into the shop.  A spray room uses a much smaller fan, but takes up a large foot print in your shop.  To be up to code, a spray room needs to be covered on the inside with 5/8" drywall, the lights need to be explosion proof, have an explosion proof fan to exhaust outside, and all electric switches need to be on the outside of the room.  This is what I have, and with the amount of spraying I do, it has been one of my best investments.