stuartshomepc
Bronze Member
Well I've been painting for over 30 years (cars, boats, motorcycles, tractors, trailers, industrial equipment etc..) and have a few hints for you.
Lately I have been restoring vintage motorcycles and here's some pic's if you want to see the some parts in case you are curious how my jobs look.
1965 Honda S90_parts.jpg
1978 Honda XR75 tank
1973 Honda Sl100 parts. Look at the shine!
First off, get good automotive grade paint. You would be better off getting your supplies from an auto paint store. Considering the amount of time that you have in the project and the money for paint, the few extra bucks for the good stuff is worth it. Rustolium (or similar $8US per quart) paint can be thinned with Naphta and sprayed, but it will not have a good finish and will never cure very hard or glossy. But it will work. I use it on tractor buckets.
Everything must be clean. Get LOTS and LOTS of white rags. Old T-shirts work great. After sanding or sandblasting wipe it down with and "wax and grease remover" bought from your auto paint supply store, or Naptha. Lacquer thinner can be used but it evaporates so darn fast that is isn't a good choice. Don't use "paint thinner" or mineral spirits. They will leave a residue behind.
You will want to prime everything with an epoxy primer or a "self etching" primer. I like the OMNI MP170 Epoxy primer (PPG makes Omni brand). It's a catalyticaly cured self etching (ie: bonds well to the metal) primer. And you can paint over in 30 minutes and don't need to sand it. If you use the MP170 add 10% acetone to it and it will lay down better. There are equivalents in the event that you cant get the omni. Just ask your paint guy. I'm not real convinced with the new urethane (ie; 2k) primers over bare metal yet. And some need to be sealed before top coating (so you would have to shoot the primer, a sealer and then the top coat).
1. With your siphon spray gun you want to set the pressure AT the gun to 50psi. 90 psi IS TOO HIGH! and it's bad if it's unregulated. I say to set the pressure at the gun as if you have 100 or so feet of hose you will lose pressure along the hose if you set the pressure at the tank mounted regulator. Just make an adapter and put a gauge at the gun. Set the pressure to 50 psi while it is passing air (ie" pull the trigger on the gun). The air pressure helps control the atomization and paint flow, so it's real important.
2. Paint..... Get a single stage automotive grade Acrylic enamel paint from a place that supplies auto repair shops (DuPont's Nason is a good value branded auto paint). Alternately the Acrylic enamel from places like Tractor supply's "restoration series" is good (but you may not have them "down under"). Make sure it is a "single stage" otherwise you would need to clear coat it. Both Dupont and PPG make single stage paints. Nason is economical and quite forgiving for a novice to spray. Don't use stuff like Rustolium or other cheap enamels. They are alkyd enamel, and not made to hold up like Acrylic enamel equipment or auto paint.
3. Use the appropriate reducer for the paint. Buy it with the paint. You can also use this reducer to clean the gun. Lacquer thinner or Acetone also works as a cleaner but evaporates fast. If you use one of these, give the gun a final rinse with the reducer to get rid of any leftover solvent.
4. If you can, get the hardener/catalyst for the paint. As it was mentioned earlier the catalyst IS BAD STUFF TO BREATH. Isocyanates cure with moisture and your lungs are a great source of moisture. It will catalyze on the fine fibers of your lungs and stay there. That's bad. Plus you build up a sensitivity to it with more use and some day just a drop will screw you up. It can cause neurological problems, lung and liver damage. Just use a real respirator and you will be OK. Wear an organic vapor respirator with a P90 or P100 filter (not a white paper mask), spray outdoors and try not to breath the vapors. The hardener will make the paint skin over faster (like 20 minutes instead of 2 hours) and make the surface more fuel resistant and more glossy. If you use the hardener be aware that it will cure all of the paint in 4 hours. So mix what you need, or in batches, and not all of it if you want some to use as a touch up later. AND make sure to clean your gun within the 4 hours. Once it catalyzes no solvent will dissolve it. That said, you don't have to use it. But it sure helps.
5. Make sure that mix everything well in clean containers and that you filter the paint as it gets poured into the spray gun. The place that you buy the paint should have paper containers and filters (most give them to you here in the states).
6. You will want some sort of a water separator right at your gun. Water will condense in the air hose and water in the paint is real bad. The auto paint stores have disposable ones for a few dollars. They are good for about one or two days of use. It's cheap insurance for a good finish.
7. Spray when the temperature is between 60 and 85 degrees F and less than 60% humidity. You can use a "medium" speed reducer. If the temp is over 85F, use the appropriate reducer (slow). The reducer speed controls that rate of evaporation and the way the droplets form in the airstream.
8. Mixing the paint. Get yourself some clean containers (not plastic) to mix in. The auto parts paint place may have some that you can buy cheep. With the paint you will see a mix ratio of say 4 to 1. 4 parts paint to one part reducer. However it's marked is the "industry standard" for low VOC (Volatile organic compounds). The helpful governments are trying to reduce the solvents (VOC's) in the air and the amount of reducers used are coming down. For a pro, the recommended ratio is an OK ratio. For us amateurs it's best to ever thin the paint by about 10% (ie: 10% more reducer). It will flow and level out better.
9. Gun adjustment on your Siphon gun. There are two adjustments that you will work with on your siphon gun. The screw on the side is the "fan" or the height and atomization of the pattern, and the other is the main needle that controls the volume of the paint. With the gun UNHOOKED from the air supply and no paint in the gun, screw the main one that is sticking out the back of the gun in all the way until is seats, then pull the trigger back and watch the needle as it gets pulled out of the spray tip. Once it starts to unseat (you are basically setting it to overcome the spring pressure that holds the needle shut) turn the needle adjustment out about 1 turn. This is just a starting point for the amount of paint that will come out. It's best to start low, and work your way up via spraying test patterns.
You can practice with any enamel paint (even paint like Krylon or rustolium, thinned with mineral spirits or Naphtha (preferred)) to get a feel for things and not waste your expensive paint. But not latex house paint.
The air fan screw will control the height and atomization of the paint. Odds are that it was factory set to a place near an acceptable starting point. Hook everything up, put some paint in the gun, get out a piece of cardboard or something flat (like a box), hold the gun 10 to 12" from the cardboard and pull the trigger for just one second. You should have a cigar shaped pattern with complete coverage in the center with fading coverage going away from the full coverage cigar shape in the center. The center should be fully covered without any runs. If you have runs, either you are holding the trigger too long, you are too close or the gun is simply applying too much material. In which case you need to screw in the material knob in. If the paint is very sparse, turn the material knob out a quarter turn and try again. You will be trying to get a pattern with a well defined 1" wide center with some fine particles on the outside, and about 8" tall. If the center is thin, open the material knob some. If its runny, close it some. If the pattern is not tall enough open the fan screw a bit. If you've opened the fan screw and the pattern is not tall enough, up the pressure 5psi and see if that helps. This adjustment is helping to atomize the paint as well as set the pattern. Poor atomized paint will not lay down well.
10. Find something like a large cardboard box to spray and practice on. You will want to spray a few 10" to 24" long test patterns to make sure that your speed of movement gives good coverage, and does not run on a vertical surface.
11. If you are at this point you are basically ready to give it a try. Spray on one light coat on your parts and wait 7 to 10 minutes for the solvent to start to evaporate. This is important otherwise the solvent gets trapped between layers and will make little pinholes called "Solvent pop" as it all finally dries hours later. Then spray a few more light coats (7 to 10 min apart) to get the color down. To get a good gloss the final coat should be kinda heavy (the paint guys will call it "wet"). It's a fine line between having it wet enough to have a nice glossy finish, and getting runs. If you get a run don't panic. Wait until it all dries for a few days and sand them out with 600, then 1500 grit wet sandpaper, and then buff with polishing compound, then wax. It will look great. However single stage paints don't typically need wet sanding/buffing. The gloss is mainly on the surface by design.
If you take your time you can do a decent job. But there is a reason that professional car painters earn a good wage.
whew... hope you learned enough
Stuart
