Spray Bomb Classics


There are many reasons why we would choose to us an aerosol or “spray bomb”. The convenience of a small container with no clean up, or the lack of a compressor, or the product needed commonly comes in an aerosol like spray adhesive. Now, I know that you are saying, “come on, what could I need to learn about spray bombs”. One of my job duties as a paint rep was doing the “defects” every month or so. I would go into the distribution center and find six or seven cases of aerosol cans among the assorted sandpaper and bondo that “didn’t work” for the customer. I say “defects” because there are very, very few actual defects, most were returned do to misuse. With about 99% of these aerosols only problem being that they were plugged up I figure there are a lot of people out there doing as I always did and some “basics” could be used.

First off, what makes the thing work? The aerosol can is simply a tank filled with compressed air that pushes out the product when you open the valve. In a 12oz aerosol can there is about 4oz of paint product, 2 or 3 ounces of solvent and the rest is the propellant (compressed air basically). The nozzle is hooked to the pickup tube that runs down to the bottom of the can into the product. If you were to turn the can upside down, the end of the pickup tube would be up at the bottom of the can in the propellant right? More on this following.

The propelent is at the top of the can pushing down on the paint product. When you push on the nozzle the valve is opened to release the pressure. The propellant pushes down on the paint product forcing it up the pickup tube, out the nozzle onto the surface being painted. About the only thing that can go wrong with this simple design is for the tube or nozzle to get clogged.

This is exactly what would happen to a huge majority of the aerosols in the defect department. There is a very simple procedure that will eliminate this.

  • First: Shake the can like it says in the instructions. Most say for two or more minutes. Look at a clock and shake it for two or more FULL minutes, not the 20 seconds we THINK is long enough.
  • Second: Turn the can upside down and give it a spray to clear the nozzle. Most of the time there should only be air at this point. You are now ready to spray.
  • Third: When you are done spraying, turn it upside down and clear the nozzle and pickup tube by spraying out all the paint that is in the tube and nozzle. Remember, the end of the tube is up in the propellant at the “bottom” of the can. It is like spraying air through a spray gun when you clean it. THIS IS VERY IMPORTANT!

If you do this EVERY time you use the can, you WILL use it till it is empty and never throw away a can for being clogged again. You can even save clogged cans with this method, I used to save cans in the defect department all the time.

Remember, there is very little actual paint in the can and it is very thin. You need to apply a number of thing coats to get good results. I have never did a mil thickness test on an aerosol but I would venture to guess it is somewhere .05 mils a coat. The average paint product shot out of a gun is about 1.5 mils (some etching primers are down to .05 all the way to high solids clears and primers giving 4 or 5).

So if you only apply a coat or two, you are not getting the mil thickness needed for good protection.

Advanced rattle can use: Aerosols you buy at the parts store are pretty limited. Limited to 1K (though there are some 2K aerosols now hitting the market). Limited to color or product you can get. But there are a few ways to use aerosol technology in your projects. You can move up to unlimited color, and product choice, even hardener!

One is to have cans “Custom filled”. This is a really neat process where the paint store puts the paint of your choice in an “empty” can (it already has the solvent and propellant in it). The “empty” can looks just like a normal aerosol, it simply has no paint product in it. The paint store employee puts this aerosol in a “press” like device. A funnel is install right into the top of the pickup tube where the nozzle fits. This funnel is actually a cylinder in which a piston is installed, after the cylinder is filled with paint product. The piston is pushed down with a manual handle or even air powered ram.

You then have an aerosol with any product you want, as long as it is compatible with the solvent in the can. They were limited to lacquer, synthetic enamel and enamel. There are now “universal” fillable cans that will take darn near anything. I have even seen a guy mix the hardener in with the enamel paint, rush home and paint with it before the paint “kicked”. Sounds crazy, but it worked.

Another way is with a “Preval” system. I don’t know of any other brand names but there may be others. This is a glass jar with a removable, replaceable propellant can that screws on the top. The disposable propellant can has the pick up tube hanging off the bottom that goes down into the bottom of the glass jar into the paint product. The top has the nozzle just like a regular aerosol. I am sure you get the idea. Any paint product can be put in the jar and sprayed. This includes epoxies, or urethanes using hardener. Is that cool or what?

Some products may need some over reducing to get them out of the nozzle. Some may not work at all because of their high viscosity like polyester primer. But your range is much wider with these two advanced aerosol systems.

One of my street rod mentors who lived near me as a kid sprayed an entire “T” bucket hot rod with aerosols and showed the car! You can get good results, just give the preparation the same respect as you would spraying it with a gun.