Painting is a subject that we probably get more questions about than any other. Since it is a very large area to cover I'm going to break it down into three sections:

1. Paint and the painting process
2. Equipment required for model painting
3. How to Mask Like a Pro

Model painting has almost a black art element to it because we are forced to use so many different materials and methods to get the finishes that we want. Is it a scale airplane? A shiny plastic looking effect? A dull flat military look? Every finish has its own idiosyncrasies and there are no definitive right and wrong ways to paint models because a variety of techniques will work for different finish requirements.

Preparation

Preparing the surface you are going to paint is the first and most important step in the painting process. Any flaws, dings or divots that are in the surface of the model will only be exaggerated when you lay paint down on top of it.

Fillers

Depending on what you are finishing, there are a variety of good fillers and putties on the market that adhere well, and very importantly, don't shrink. For that reason avoid one-part glazing putties -- they shrink like crazy. My personal favourite filler is a product called Featherlite but there are many other good ones on the market. Featherlite is a two part putty used in the autobody industry. It is very light, sands extremely well and a tub of it will finish about 100 models. I've used it on both fiberglass and balsa and it seems to stick well to either of them. Expect to pay about $30.00 for the kit.

Sanding

I should also mention that when you are sanding the surface of your model, be it fiberglass or balsa, don't use your bare hands and fingers. Use a sanding block. It is impossible to get a flat, consistent surface using your bare hands, I've tried and it doesn't work! I've created so many differently shaped sanding blocks for different surfaces that I now have a box overflowing with them. The commercial ones are excellent and useful but you'll find there will be many places that will require you to create a "one off" to get into those tight spots or irregular areas. Balsa blocks are excellent for this purpose since they shape easily, and when sprayed with 3M adhesive, hold sandpaper great.

After you have a surface you're happy with, straight and true, it must be prepared for the first coats of primer surfacer that will act as the final fill for the paint to be laid onto.

Balsa-wood Preparation

A balsa-wood surface or a fiberglass one will determine on how much work you have remaining before you can actually spray some paint. If it's fiberglas you can skip to the next paragraph, if balsa, sit down, class is still in session! The most common way to prepare a fully sheeted surface for paint is to cover it in 3/4 oz glass cloth and coat it with a good laminating resin such as Pacers Z-Poxy. This accomplishes a few things. The first is to give a tough surface that will resist dings and secondly to provide a stable surface that won't shrink or crack when the primer and paint is laid on top of it.

A word of caution: Only use as much resin as required to fill the weave of the cloth, anymore and you are adding unnecessary weight. After the first coat you will be left with a surface that is hard and stable but will still require more filling. Take some 320 grit sandpaper and lightly sand the fuzz off the surface and if any obvious low spots are apparent, now is the time to fill them.

After you are happy with your surface, lay on another coat of resin to completely fill the weave of the cloth, once again, just enough to fill the weave. Again, lightly sand the surface to take off any high spots. This should leave you with a surface that is very flat, smooth and ready for primer. Phew!!

Priming

The next step in this sequence is to lay down a primer-surfacer of some kind. This step accomplishes a few things. First and foremost, it acts like a final layer of putty to fill those minor imperfections that will still exist no matter how meticulous a finishing job you may have performed. This is where some judgment and decisions have to be made since the primer you use will have to be compatible with the paint you plan on using for the final surface coats.

If you are going to use spray bomb paints then be forewarned that you would be best advised to stick with spray bombs for the rest of the job. The single part paints are easy to use and don't require spray equipment but they are not nearly as stable as the two part systems. I have had some nasty -- and I mean NASTY -- reactions when I've tried to lay down different types of paint onto one-part primers. Everything from lifting the surface underneath to the paint never curing properly on the surface. For that reason I would recommend using a two part primer for the base.

The automotive world produces some excellent epoxy-based primers that are not as toxic as the polyurethane based paints. Check locally for a source near you. When you apply the primer don't be shy about putting on heavy coats since most of it will be sanded off anyway. Two or three wet coats should do it, allowing each one about 15 minutes to flash off before applying another.

More Sanding..

After the primer is applied the real work begins. You will now go about sanding virtually all of it back off. Don't get lazy here or you will have unnecessary primer on the surface that has no purpose at all, other than adding an enormous amount of weight to your airplane or helicopter! After you have sanded, sanded and then sanded some more, 9 times out of 10 you will have to shoot another coat to fill the low spots you didn't see on the first go round.

Professional painters will use something called a guide coat to let them know if they've hit all the low spots or not. Essentially this involves spraying a very light, dark (usually black) coat of paint all over the surface that is going to be block sanded. When you do start blocking the surface it is very obvious what parts are low and will require more filling since they will still have the guide coat remaining. Once you have a surface that you think is free of imperfections and irregularities, you can start to apply the colour coats.

Painting

Automotive Finishes -- Danger

A note about automotive paints. All the products used in the autobody industry give excellent finishes but they have some serious draw backs. The largest one is the issue of toxicity. Most of the two part auto paint catalysts contain something called iscocyanates. I won't pretend to be a chemist and try and explain what this stuff is, but it's primary job is to perform a chemical cross link when mixed with the paint that gives that bullet proof and shiny gloss to acrylic enamels and base coat/clearcoat systems that are used universally in the auto industry. The down side to all this wonderful chemistry is that the stuff is lethal even in small doses.

Professional painters use a respirator system that pumps fresh air from an outside source to a self-contained mask and suit so they can avoid all contact with it! A simple carbon activated respirator does not work. The byproduct it produces is odourless and cumulative, meaning you're system never purges it, it just accumulates in your organs and central nervous system until something finally packs it in. I don't want to seem melodramatic about this but everyone in the autobody industry I've talked to has said the same thing, unless you've got the knowledge and access to a spray booth, don't use the two part isocyanate catalyzed paints.

Other Finishes

Now that I've terrified you from ever painting anything again I should say that most of the paints we have at our disposal are not nearly the "bad boy" that the isocyanate paints are. In fact the single part base coats that are the standard of the autobody finishing industry are not nearly as toxic (a normal carbon activated respirator is fine) and come in a mind boggling array of colours. I use them all the time. These finishes must be clearcoated (here comes that nasty isocyostuff again) but you can either use a much less toxic epoxy clear or get your local friendly autobody guy to clearcoat it for you. The cost involved is minimal relative to you're health, don't you think?