HVLP Tip Size

      Too small a spray-gun tip will dry wood finishes and require too many passes for adequate build. November 11, 2006

Question
I run a one man shop making custom furniture and until now, I have had all finishing done out of house. My first attempt at spraying lacquer went fairly well, however it took four coats. I'm spraying a gloss moisture resistant lacquer from Sherwin Williams out of a Sharpe gravity feed HVLP. The tip size in the gun is 1.4mm. Is this tip size right for the application? I realize that my sprayer is primarily designed for car stuff, but Id like to make it work if possible. They make 1.4mm, 1.6mm, 1.8mm, 2.3mm tips for this gun.

Forum Responses
(Finishing Forum)
From contributor H:
Since this is your first spray attempt, you might want to experiment with some scrap material and go up a tip size. You were probably doing yourself a favor by using a smaller tip till you got the hang of the gun and proper speed. Spray tips and needles are nominal in cost, so it might be worth the bucks to go up a size or so.



From contributor L:
I use ML Campbell's MagnaMax and it has a viscosity rating of 30 seconds in a #4 Ford cup at 77F. With my gravity feed cup gun, I use a 1.7mm tip and a 1.9mm cap. They are supposed to be matched, but I find the larger cap gives a better spray pattern. I also thin my lacquer with 7% standard thinner. I end up using 2 coats for a final finish. If I am spraying fully assembled cabinets, I thin to 15% and they get 3 coats. This should give you a starting point to get you going.

From contributor R:
1.8 would work best on that gun.


From contributor D:
Why are you using Sherwin-Williams Moisture Resistant Lacquer? I used to use it until I read the tech sheet. All the finishing has to be completed within a day, however many coats you put on. I ignored this limitation with no bad results (recoat window possibility), but I also did not want to always be a maverick. I like finishing within the confines of a tech sheet.

Not only that. As a furniture lacquer, this stuff is too soft for my likes. Compared to retail furniture, like what you get from Thomasville, the Sherwin-Williams lacquers are too soft. I prefer a harder lacquer (I like Kwick Kleen's lacquers). Lacquers differ in how they perform on the pencil hardness test, product to product, brand to brand. Lacquer users do not realize this and the manufacturers do not publish pencil hardness tests on their lacquers. The hardness of a lacquer is just one parameter of the coating that I like to know about. It matters in my selection of a product.



From contributor W:
We usually do not recommend the 1.4 tip set. This is an automotive size, not woodworking, and it is generally too small for most wood products, dries the spray, and you have to put down too many passes. Since so little material comes out, many people also tend to cut down the atomizing air, which also decreases the gun's performance. We generally recommend a 1.7 or 1.8 mm for standard wood lacquers and pigmented lacquers. For the thinner lacquers, we recommend a 1.5 or 1.6mm tip set. Many other factors will affect your choice in tip. However, since your gun has the other tips available, you are in good shape. Start with the larger size and see how you like it. You should be able to get a 1 to 2mm build per pass and need 2-3 passes. Some of the factors you can look at are the tip size, the viscosity of your material, the temperature of your material and also your air, the ambient temperature of the room, and the thinning agents and curing times.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor T:
Considering the problem, it is always best to upsize and speed up. You can always slow down, even in the middle of an application. I've never found any product that can be sprayed effectively without thinning the product, unless a chalky finish is desired. I know what the data sheet says about MRL70, but I've never had a problem if I sand with 220 or 320 first. Don't forget if it runs, you're moving too slow or too much overlap on application, not that the material is too thin.



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