Replies

1. 
   mudman | Dec 19, 2006 09:53pm | #1

   The problem is not the gun, at least not from what I read from you so far.

   First of all oil based enamels (house paint) are the second most difficult finish to spray, Latex house paint is the hardest. If you read the can it will almost certaintly say not to thin more that 10 or 20 percent. I have a 4 stage Fuji so my set up should be pretty close to yours. 20% Penetrol or straight linseed oil and 30 to 40 percent paint thinner (not pure mineral spirits, paint thinner has additives to help). So the ratio would be like 2 parts penetrol, 4 parts thinner, and then start with 6 parts paint and reduce untill it sprays. Use the drip cup thing if they provided one. You will find that even at these thinning ratios it will be too thick according to the drip cup but it will give you an idea.

   You will need a large tip. I don't know the sizes that Apollo uses, but it will be the biggest or second largest. The tip you have will likely do the job just as well (not very good). You will have to turn the air all the way up and keep the hose as straight as possible to keep the air flow high. It will be best to not spray a fan pattern, but regaurdless keep the spray pattern tight. All of this will give you the best air flow concentration to atomise the paint. Then turn the fluid adjustment (paint flow) very low. With the fluid turned down very low you should get good atomisation. Keep the tip about 10" from the work surface, any farther and the finish tends to "de-atomise" for lack of a better term. With this set up you will have horrible overspray!! So slowly turn up the fluid untill the paint stops atomising properly (you will start getting unacceptable droplets or globs). The more fluid coming out the better your overspray ratio will get, though there wil still be a lot. Then dial it back untill it atomises good again, you will then have the gun set up as good as possible.

    The thinner the paint, the better it will atomise. But you run a greater risk of comprimising the integrety of the finish. Remember the can says no more that 10 or 20 percent thinner, so you will be WAY out of the tested paramaters for the paint. I have used a few popular premium brands and have not had a problem with the ratios I gave above.

   No matter how hard you try the finish will not be very good. By the time you get the paint thin enough to atomize nicely it would certaintly not cure well. The overspray will be horrible and it is a very sticky persistant overspray. Because of all the additives each coat will need 6 to 8 hours to dry enough to sand. In that time there will be all kinds of dust contamination. Adding Jappan drier dosent help. The key is to prep throughly. I use Zinzer BIN primer tinted to the top coat. This is a shellac based primer that dries fast and sands very nicely. Apply 2 or three coats and sand with 220 between each untill the surface is perfectly smooth. then spray two very thin coats of the enamel.

   I tried to list this stuff in the best order, but in practice you will have to go back and forth between mixing and trial spraying to find the best comprimise of thinning and gun set up. Here are some rules of thumb listed in no particular order.

   -Prep. Prep. Prep. Prep. For solid colour finishes the surface needs to be grain filled, leveled, smooth and sealed. Clear finishes are a lot more forgiving.

   -The thinner the finish the easier it sprays.

   -More air = better atomization but more overspray.

   -The larger the spray pattern the poorer the atomisation. Using the fan pattern reduces effeciency even more.

   -The farther away the gun is from the work surface the larger the pattern gets and it is less likely you will get runs, but you will get more "dry fall" (droplets of finish that dry too much to flow together, giving a rough texture). If the gun is closer the finish will go on "wetter" and will flow togather nicely.

   -The more finish going to the tip (fluid adjustment) the wetter the finish goes on(wetter is good) and the quicker the coat builds, but the atomization gets worse and runs are more likely. The tendancy of most people new to finishing is to move the gun farther away when the fluid adjustment is too high, this adds to the problems. If you ar keeping the gun more than 14" away turn down the fluid.

   -You need more air to atomise more fluid. All setups have a practical limit to how much air can reach the tip. With a turbine system once you hit that limit there is nothing you can do. With compressor systems you can turn up the pressure but the gun will start spraying eraticly and create a fog of overspray. This means there is a definate limit to how much you can spray.

   -How you hold the gun, move it through the pass and maintain the gun perpindicular to the surface are also key to a good finish. I have seen a few people who are simply not able to get the coordination down (one is my helper).

   After reading all this you might conclude that spraying oil based enamels (or any house paint) is impossible. And to a degree that is true! There are finishes that are designed for air guns. The thick stuff you buy at Home Depot is best used in an airless pump. The easiest solid colour finishes are lacquers. Sharman williams is one of the most prolific suppliers for woodworking. However, unless the project you are working on is of heirloom quality I say keep on trying. Get a bunch of cardboard boxes and spend a day mixing, spraying, adjusting, spraying, remixing. Then sleep on the experience and go for it the neaxt day. Once you figure out how to spray house paint you will ba able to spray ANYTHING.

    

   Pardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

1. 
   Meilcowski | Dec 27, 2006 08:33pm | #2

   Wow,

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   That was a lot of information. I tried mixing the enamel to the proportions that you provided, it work really really well. I was impressed. It was a name brand enamel and I didn’t seem to loose much pigment by diluting it. I put on a couple of coats and that penetrol just flowed fantastically.

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   I am printing your post and keeping it in my files. Thank you for all the help!

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   One more question though. If I wanted to spray something white, what would I use instead of enamel or latex that is not really difficult to spray? Is there another product out there that performs better that the White Enamel? Is there such a thing as white lacquer or something like that?

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   Thanks

   Edited 12/27/2006 12:39 pm ET by Meilcowski