Troubleshooting Overspray Lines with Pre-Catalyzed Lacquer

      Overspray lines on a large piece may show up because of air pressure, drying time, nozzle settings, speed of application, and other adjustable factors. May 11, 2006

Question
I made solid birch table of 102" long by 44" wide, stained dark walnut. I'm using Mohawk's pre-catalyzed lacquer; I can't seem to get a consistent finish. Thereís always a line of frost it seems. Iíve tried reducing my product (it was spraying better) but the lines were still there. Iíve tried using a no-blush retarder but the lines were still there. Iím spraying with Sata gun and my shopís compressor which I spray at 35 pounds. I also tried to adjust my spraying technique (closer and farther) to the table and also spraying wide shot with narrow shot. Iím spraying in my paint shop that I built this summer. Is this the project thatís finally going to make me purchase an HVLP system?

Forum Responses
(Finishing Forum)
From contributor A:
Try reducing the pressure Ė you may be getting more at the gun than you need.



From contributor B:
Have you tried spraying a smaller piece? Sometimes that will tell you if the problem is with the finish, the gun or the spray technique. Definitely try and lower the air pressure to its lowest tolerance (make sure you are still getting proper atomization). Also find out the specs on the finish and it should tell you how much retarder you can use. If the finish you are spraying is a clear topcoat (no tints) you may try spraying across the piece rather than long ways, the shorter passes will help keep your wet line fresh.


From contributor A:
Sometimes, the pressure gauge at the compressor maybe off, and this can cause that problem. You should buy a pressure gauge that fits near the gun, so you know what pressure is going into the gun. This also will make it easier if you want to adjust the gun's pressure for different work.


From contributor C:
I am not sure if this applies to your problem but it is common that finishers will have difficulty with overspray lines when using guns that are too slow for the size project being sprayed. It is possible to spray a vehicle with only an airbrush but there is likely to be a lot of rubbing out involved. Same is true of spraying cabinet parts. Faster drying material makes the equation more sensitive. I like to be able to spray an entire cabinet door and then make a quick inspection running the light across the door and still have time to respray any thin spots. You have to move quickly to do this and your gun has to keep pace too.


From contributor D:
Speed on large surfaces is crucial. The fastest delivery system is AA but HVLP pressure fed or conventional should work if you are able to slow down your tack time. Retarding the coating should give you better results. Are you sure you have proper fluid nozzle and air cap?


From contributor E:
Doesnít that just chap your hide when the gremlins decide to pay you a visit? Besides the expert advice youíve already received, Iíd also check to make sure your air cap is clean and free of obstructions. Sometimes dried bits of finish or a sliver from a wooden stir stick can lodge within the air passages of the cap. Something as simple as this can throw off your spray pattern.


From the original questioner:
I have a water separator in my paint shop and that has a control valve in it which I adjust. Iíve tried spraying with the grain, against the grain, applying a lot lacquer, a little lacquer. My spraying method is to over lap half way on the previous lap, the job looks awesome and then when its starts to dry, the frost lines pop out. Iím using a Sata gravity gun and my hose size is 3/8. My lacquer is dry to touch in 5 minutes and re-coat in 1 hour as per specs. I have no idea what my nozzle specs are - what should I be looking for?


From contributor D:
You mentioned earlier in the post that you were thinning the lacquer - is it the Mohawk brand ?


From the original questioner:
Yes, all Mohawk products. I was also thinking that it might be the companyís mixture of pre-cat lacquer that is off.


From contributor F:
It's not clear to me, but I infer you spray across the grain, with the grain, with an hour between coats. Most of us would spray across the grain and then with the grain - with no time between coats, wet on wet. I have seen your problem when trying a single pass top-coat.


From contributor A:
Try spraying a different coating on a clean piece of wood to see if you get the same results. It should tell you something.


From contributor G:
I agree with contributor F - wet on wet, and also slowing down the dry time by way of retarder or flow enhancer of some type that works with your product. The surface is large enough that you'd want to hurry with the coat and make it full/wet enough to evenly dry. You're fighting the dry time, perhaps booth air, too much air from the gun, or all the above. Dry to the touch in 20 instead of 5 perhaps. Give the material time to lay down and melt evenly.

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