Spraying Shellac

[Jim Foster]

I recently acquired a Central Pneumatic HVLP Gun (66222) from Harbor Freight. It has 1.4mm tip on it. I'm going to spray a paneled section of White Oak with Zinsser Bulls-Eye Shellac in the next couple weeks, I'll apply it over a Watco wipe on finish. The can comes in a 3lb cut, and the manufacturer suggests cutting it in general, but does not make any suggestions for HVLP spraying.

On my own, I"ll probably set the pressure around 35psi at the gun and try to tune around that pressure and the 2lb shellac cut on some practice materials. My compressor is more than big enough, and I've got the air filtered at the compressor and at the gun. Humidity will be around 30%.

If anyone has any advice to offer on a better lb cut for the shellac or pressure setting to start with, I would appreciate the suggestions. As a first time user, it seems like having a good starting point for the variables mentioned, (Cut and pressure) setting the spray on practice pieces should not be too difficult. Also, the gun does not come with a viscosity cup, and the directions mention something about the material dripping at a rate of 1 drip per second to be of the right viscosity for the gun, which seems a little tough to measure properly to me.

[Jason Roehl]

I can't speak to PSI or tip specifics, as I just test and fiddle with whatever I've got at the time until I get it right, whether that's my own cup gun and compressor or on a job using someone else's turbine HVLP or turbine/compressor HVLP.

I have sprayed plenty of SealCoat, which is a 2lb cut. One thing is don't over-atomize and/or try to put it on too thin. If you have the spray down to a very, very fine mist, you will just be putting a huge amount of material in the air that will settle later as dust, and you'll have lots of dry-spray near where you're spraying. That is, if you're spraying a wide, flat surface, by the time you're making your last passes, your first ones will be tacking up, and you don't want to be throwing tiny droplets in that direction that will sit on the surface without "melting in". Whatever I'm spraying, I like to be able to spray it quickly enough that the whole thing is still wet when I'm done with a coat. With shellac, that is tricky, but not impossible, depending on the piece.

[Prashun Patel]

I would get the Sealcoat like Jason. I have sprayed a decent amount of it from my elcheapo sprayer from Woodcraft. It sprays just wonderfully. I can tell you about nozzles and whatnot, but I just dial my spray back to the lightest mist possible, do three quick passes, wait 5-10 mins, and repeat.

However, I have to ask why you're doing this over Watco. It won't offer more protection vs the Danish Oil (if that's what the wipe on finish is). Shellac isn't usually used with oil/varnishes like this.

[John TenEyck]

I generally cut Sealcoat with 50 DNA when I spray it, so that means a 1 lb cut. I would cut your 3 lb cut at least 50% to a 1.5 lb cut, or more. Viscosity's not the concern, it's more to do with being able to put it on uniformly in a thin layer. The more you cut it the easier it is to do that. At 30% humidity I might use Behlen's Behkol alcohol instead of DNA, too, so it doesn't set up so quickly. Others add turpentine to DNA to achieve the same result, but I've never done it. I use a 1.4 mm HVLP gravity feed gun, too, and run it around 20 psi inlet pressure at the gun. 35 psi sounds way too high to me, although maybe that would be a good starting point with a 2 lb cut.

John

[Jim Foster]

I have to ask why you're doing this over Watco. It won't offer more protection vs the Danish Oil (if that's what the wipe on finish is). Shellac isn't usually used with oil/varnishes like this.

I've played around with several finishes for this Q-Sawn White Oak project and this looks the best, I got the idea from Bob Lang, http://www.popularwoodworking.com/techniques/finishing/authentic-stickley-finish-with-modern-materials


I generally cut Sealcoat with 50 DNA when I spray it, so that means a 1 lb cut. I would cut your 3 lb cut at least 50% to a 1.5 lb cut, or more. Viscosity's not the concern, it's more to do with being able to put it on uniformly in a thin layer. The more you cut it the easier it is to do that. At 30% humidity I might use Behlen's Behkol alcohol instead of DNA, too, so it doesn't set up so quickly. Others add turpentine to DNA to achieve the same result, but I've never done it. I use a 1.4 mm HVLP gravity feed gun, too, and run it around 20 psi inlet pressure at the gun. 35 psi sounds way too high to me, although maybe that would be a good starting point with a 2 lb cut.

Thanks, I will start with 20 PSI in my practice work and also use a 1.5lb cut to start with and see if I can get it right with a minimum of trial and error.