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Thread: need advice on spraying shellac

  1. #1
    Join Date
    Oct 2003
    Location
    Acworth, GA
    Posts
    67

    need advice on spraying shellac

    I've decided to try to step up to spraying finishes. I've acquired a Harbor Freight 43430 gravity fed hvlp gun. My first step will be spraying SealCoat. I understand that SealCoat is about a 2 lb. cut as it comes in the can. Is this a good consistancy for spraying or should it be thinned? How do you determine the proper consistancy in general? Is there a magic formula depending on what you're spraying and which gun you use or do you just try it and see if you like it?

    Bob

  2. #2
    I don't have an HVLP gun, but spray shellac in an automotive touch-up gun without too much problem other than overspray. I think 2# is what I have sprayed.

    Practice on something first. Add some alcohol and try again. If the out of the can was best, do that. If not, keep adding alcohol (you are writing the amount added to a given volume aren't you) until it's what you want. (Temperature and humidity will affect the results.)

    Good luck, I love the smell!

  3. #3
    Join Date
    Sep 2003
    Location
    Philadelphia, Pa
    Posts
    2,266
    I spray shellac, and it is an excellent product. Be sure to strain the shellac. Just a regular paint filter will be fine. About 10 cents or so. I cut it a bit, but not too much. Perhaps 10%. Jeff Jewitt sells an additive, the name of which I can't recall, that slows the drying down a bit and will help eliminate a fat edge. If you get a run, no problem. Just keep a clean white rag handy, with some alcohol, and wipe it off, and keep going.

    You can also color the shellac with Transtint dyes. But, don't sand the dyed coats or you may get a bit of unevenness in color. Instead, clear coat over the color coats, and then sand. With the color, go gentle, and use a couple of coats or otherwise it is easy to get too much, and taking it off is a PITA. (Is PITA alowed?)

    Have fun. Spraying shellac can give you 4-5 coats a day, and I leave mine in the gun all day if it is a spray day, and only clean at the end.
    Alan Turner
    Philadelphia Furniture Workshop

  4. #4
    Join Date
    Feb 2003
    Location
    Chappell Hill, Texas
    Posts
    4,417
    I've sprayed a lot of shellac. Sealcoat, for my taste, is ready to shoot right out of the can. I'm not familar with that HF gun. Get some cardboard, or scrap plywood, or a roll of butcher paper you can rip off and toss in the trash and practice in a vertical mode until you get comfortable with the flow and pattern. Horizontal is easy - a thick wet finish resting flat won't run as easily. Shellac will run quick, so dryer coats are better than wetter coats.

    My approach to spraying shellac is this... you are going to be rubbing it out anyway, so why waste time trying to get a perfect finish by spraying the perfect coat? Just get it on there and build it up. Do 4 or 5 coats in a day. After the first coat dries for about an hour, sand with 220 FRE CUT paper, then get the other coats on there. Let it dry overnight and the next day 220 or 320 it again. No muss, no fuss.

    With a gravity gun, you are limited in the positioning and angle of the gun more so than with the other styles of guns. If you will be shooting inside a cabinet or box, or at weird angles, plan your route ahead of time and maybe rearrange your project mid way through so that you can achieve consistent coverage.

    Being new to spraying, there are a few things you should read up on:

    There are measuring devices that tell you the viscosity of fluids. There are several types: Ford cups are one style, and there are others (can't remember...). Basically how they work is you fill them up with what you will be spraying and time how long it takes for them to drip out the little hole in the bottom of the cup. (Measurements like "4 seconds in a #2 cup", or some such specification. I don't know that Sealcoat specifies this on the can, but maybe you could find it on the Zinsser web site.

    Also there are fluid and pressure adjustments on your gun (I'm assuming). You'll want to find the right mix to give you a good pattern. There is a technique to holding the gun too (distance from the work, speed at which you move, angle of the gun, how you overlap passes, how you shoot off the edge, etc., etc.).

    There is also a thing called a "wet mil gauge". This is a business-card shaped piece of metal, (maybe plastic), kinda-sorta notched like a trowel around the edges, but the notches are different sizes and stepped for height. How it works is that you spray a section of wood, and while it is wet, you place the edge of the gauge in the wet finish and remove it. Depending on what footprints it leaves in your finish, you can tell how many mils thick your wet coat is. Again, most quality finishes will give you a specification for how thick you should be spraying, ie, 4 to 5 wet mils per coat, two coats, or whatever. There is also a dry guage too, but I haven't used one of those.

    Both the viscosity cups and the wet mil gauge are tools I don't use everytime I spray. But, when you or I are learning, or spraying a finish that we haven't sprayed before, or are in doubt, or we're having issues, they are excellent aids to confirm what we might otherwise be guessing at.

    Hope this has helped. Todd

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