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Spray Painting

Written by David Jackson

Friday, 15 September 2006

Fish eye and orange peel

The mere thought of spray painting can cause Johnny Modder to whimper and cry. “All those runs! Fish eye and orange peel,” says Johnny. “Everything I paint turns out bad!” Yet, with some simple surface preparation and a few techniques that are easily learned, Johnny can paint like a pro. Along with this article, the current Modcast series, "Pimp My Mac" by John Hart, has extensive guidance on this subject, so both you and Johnny will have plenty of tools to prevent an "Orange Peel Mac"... unless, of course, that's your desired effect.

First Things First
Get the right paint for the job. You don't want to get latex to paint the metal parts of your case, nor do you want oil-based to paint the plastic. Generally, you want an enamel of some kind or the new plastic paint that bonds to plastic on a molecular level. (Yes, I said "molecular level". Don't worry, I looked it up first.) Although it's important to get the right paint, it's equally important to prepare the surface properly. This means sanding and cleaning. You want the surface to be clean and smooth, but not slick; paint needs a surface with a little “tooth” to stick to. Imagine a piece of glass. It's so smooth that you could spray a couple of coats of paint on it then peel them off once it dried. Now take some fine sand paper and “rough it up” a bit and the paint sticks and can't be removed. The glass now has some “tooth”. Clean with TSP (Trisodium Phosphate) or some other detergent, then sand, then clean again. And, just to be sure, use a tack cloth, a cheese cloth type material coated with a sticky substance that picks up almost all the remaining dust.

Now, on to the painting! Maybe? Well, almost. Next, we must have a proper work area. This means a well ventilated and dust free zone. This can be accomplished by building a small room out of plastic sheet near a window. In a garage if possible. (The wife doesn't like it when I build small plastic rooms in the house.) A fan in the window and a table to paint on, and you are almost ready to go. You need a good light source. Halogen work lights are inexpensive and very bright.

If the parts you are painting are small enough, you can make a spray booth out of a larger cardboard box. Of course, if its a nice warm day with low humidity, then the sun is your best light source and you don't need the fan or the plastic room if you are outside. I would, however, recommend a respirator no matter where you are spraying, or at the very least, a good dust mask. Basically, don't copy Mr. Hart on this one: a respirator is a MUST. Also, I have found the trigger attachment for spray cans to be very helpful in preventing fatigue and aiding in control.

Time to Start
Now that you're set everywhere else, it's time to Prime. Primer fills small scratches and adds “tooth” to make the paint adhere more readily. The only time you would omit this step is in the afore mentioned plastic paint that has the molecular bond. (Ha! Worked in in twice!) Spraying primer is very much like spraying the paint except primer tends to be more forgiving when it comes to runs or sagging. You should still take care to spray several light coats, not one heavy coat. The method of spraying is of great importance. The following illustrations show the most common error in paint application and the proper way to apply the spray. Again, "Pimp My Mac" will be enlightening as well.

The picture on the top is an exaggerated example of poor spray technique. You don't want to “fan” the can. In the bottom picture you see the proper way to spray. Holding the can parallel to the surface, start spraying. After you start moving your hand and just before you reach the part to be painted. And continue spraying after you reach the other side for a fraction of a second. Doing this ensures a good coverage to the edge of the part. Hold the can around six to eight inches away from the surface, or as directed by the instructions on the can.

Tips
Don't try to get it done in a hurry. Multiple fine coats produce a far better looking finish than one or two thick coats that sag or run. Check the can for re-coat time and wait the given amount of time between coats. It's usually not very long, sometimes as short as fifteen minutes. After that final coat, don't touch it! Let it dry for at least as long as stated on the can. There is nothing worse than finishing a great paint job only to mess it up with fingerprints in the paint.

'Till next time, Keep Moddin'

Editor's Note: Jason Schrader's "Killer Bee", which won "Best Mod Guide" in The Great Mac Mod Challenge 2006, also has some great instructions. With John Hart's series, David Jackson's article and Maestro's guide, everybody on MacMod.com should be able to do a great paint job!

Comments (2)

	03-08-2008 22:22
	If you want a shiny finish like you see on cars then you need to flat the panel using wet and dry 1500. add a little washing up liquid to some warm water, be sure that you keep wetting the sandpaper. when you have finished lightly sanding you need to clean your panel. then next spray some clearcoat about 4-5 layers. when thats finished you can leave it as it is or use some rubbing compound to get a really good shine. Guest

lisa merrick

	19-03-2007 12:11
	I have found it easy to use a petroleum based cleaner for metal and for plastic plain old windex to clean a surface after sanding. If you have a big dishwasher that will do wonders as well but you want every inch of the project to be dry. As for the paint you can get a mirror car like shine with using a enamel paint used for car engines. The paint runs about a dollar more then most spray paints and comes in a spray or brush forum. This way you don't need to sand or do much prep on the metal work. With the plastic you of course want to sand the plastic a bit. Scuffing it doesn't work too well depending on the plastic. A lot of thick oil based plastics need a lot of sanding. You can use a enamel paint for the plastic as well but you should use a primer. The best primer I found is filler primer. This stuff will fill in scratches and such. You can use a thick coat of primer then sand it again to get a smooth body then paint the color then do a wet sand if you have the time and effort. Theres a wax called Carnauba Polish that re moves the haze/swirl from the spray paint and will give you a very nice shine. After using that you can add your clear coat then use the Carnauba Polish again to make the clear coat pop that coat of color. Registered

TCPMeta

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