Kerry Verne
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« Reply #20 on: June 16, 2008, 11:23:08 AM » |
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Here's other Lacquering tips from another thread.
Eric Fuller said:
HVLP Finishing Primer
Finishing puzzles with an HVLP sprayer and lacquer is a very efficient and cost effective method. Here's a primer:
TECHNIQUE AND TIPS
You will need a large flat surface to spray on. I use a 36"x80" luan door I bought at home depot for $20. It's nice and flat and offers a lot of room to work on. Flat is important when you are spraying small pieces, because if the surface is bowed or uneven, the force of the air jet coming out of the gun will rotate them, making it difficult to get even coverage. In fact, having the airflow push your work around is the main challange to finishing puzzles with a sprayer. HVLP spraying works better the closer you get to the work. On large pieces, professional sprayers will spray from 2" away. On puzzles this is tough, but in general you want to be spraying as close to the surface as you can without having the piece move about.
One tip to keeping the pieces in place is to intentionally "prime" your spray surface with an orange peel finish. Just spray it from afar with straight lacquer until you get a nice nubbly finish. This will help keep smaller pieces in place down the road.
I tend to space my pieces out in a staggered pattern of rows. Then I spray them from above at each corner angle (think of holding the gun at a 45 degree angle both vertically and horizontally, pointing down on the piece), so that each pass has the chance to get into three sides and any exposed internal corners. This works pretty well because the top will get four passes, but the sides will only get two passes. When you flip the piece over and do the other face, the sides get two more passes and the bottom gets four. Before you break out your calculator, that means each face gets four passes for optimal coverage.
Endgrain will many times absorb more lacquer than side or face grain. If I'm working with pieces which have the endgrain uniformly accessable (like standard square burr puzzle pieces), I'll stack them up on end and do a fairly heavy coat directly on the endgrain to saturate it before I start the rest of the puzzle. On more complex pieces where you cannot isolate the endgrain by stacking, you may consider doing a heavier coat so that the coverage is more even.
You want to hold the gun within 4-8 inches of the work. Sometimes this is difficult with smaller pieces as the strength of the air will push them around. In that case you need to spray as close as you can, and use a heavier flow. With smaller pieces you really have to watch out for overspray (see below), and use more retardant.
For spray technique, go back and forth in even, overlapping strokes. At the end of each pass you want to overshoot the last workpiece so you don't have dwell time on it when you switch directions for the next pass.
Remember that you will be making four passes on each face. If you see immediate heavy coating on the first pass, you'll likely end up with too much by the time you get around to the final pass. The application is cumulative, so start out light and work your way up until you are happy with the results of the sum. Obviously you want to spray roughly the same size pieces in batches - if you mix very large and very small pieces, your coverage will by necessity vary, with potentially poor results.
A final note about lacquer in general - it's very forgiving. If you spray too heavy you can fix it by dipping the piece in thinned lacquer and hand drying it. Since later applications melt into previous applications, you can always go back and reverse mistakes...sometimes it means doing each piece individually though, so be careful.
OVERSPRAY / ORANGE PEEL
Overspray is when the individual droplets dry before they hit the piece, only to be covered by larger wet droplets. This can happen easily in warm or dry weather because the air coming out of the turbine is already heated from being compressed, and will leave you with a bumpy texture. The lighter you spray, the more potential for overspray. Also, if the lacquer dries before it has a chance to flow and level out over the piece you can end up with "orange peel", which is a bumpy texture to the finish.
The solution to both of these problems is to use lacquer retarder. It slows down the rate of drying and avoids overspray. It also allows the lacquer to level out before it dries, giving you a nice smooth finish.
It can be tricky to determine how much retarder to use, as it will depend on the conditions on the day you spray. If you have an indoor spray booth set up it is easier since you have more control over the climate, but indoor rooms pose a great fire / explosion risk, and need to be carefully designed. I prefer to do my finishing outdoors. This can bring about its own set of problems though, since any wind above a couple MPH will make it nearly impossible to maintain even coverage. I check the forecast for calm days, and my spray area is well sheltered by three walls.
I generally start with the spray cup 1/2 full of pure lacquer. I gradually add retarder until I am able to spray test pieces of the same size and have the piece immediately wet to the touch, but fully dried within a minute or two. The amount of retardant will vary with each project, since you will be spraying different sized pieces (hence using different amounts of flow to compensate for the distance between the gun and the pieces) and the climate will be different. That's why it's important to have a lot of test pieces of roughtly the same size, so that during the setup phase you can determine how far out you need to hold the gun and how heavy you need to spray. Once you hit the right mixture, make a note of it so you can refill to proportion later on.
FINAL NOTE
Lacquer can have some really nasty side effects if you breathe a lot of it. You DEFINITELY want to buy and use a respirator for this work.
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