In this section I will cover the pros and cons of painting using off the shelf aerosol cans, but getting a finish to be proud of and far superior to just spraying and letting it dry.
Many people buy cans because they are easy to use, but in using them, the finish they get is not as they would have hoped for. I will show you with a small amount more work, the different between just spraying and spraying well.
So to demonstrate can spraying, I will just spray the same length of metal two ways. One side will be just sprayed from the can, and the other side sanded down between coats, and at the end you will see the difference you can achieve with a small amount of extra work.
The paint I am using is just straight from the auto shop car body spray paint. I am using a red oxide primer first, then matt black, then finally a clear gloss lacquer.
Its actual easer to spray with matt paints, and then lacquer over them when finished. Matt dries off much quicker and can be handled far sooner than gloss, which takes ages to dry, and even after a few hours you can mark the surface if you press to hard. Gloss also tends to clog the sandpaper, even using wet and dry.
The same technique is used if spraying plastic and resin, and while some plastics need a proper plastic primer, most resins actually spray better with auto metal primer instead of the plastic primer. The auto primer actually softens the surface of the resin very slightly which means it adheres far better.
The first thing to do before anything else is clean the item to be sprayed. In the case of metal, you can use just about anything sprit or chemical based to clean up the surface, but if cleaning plastics, you need to do a tiny test area somewhere it wonít show to make sure the cleaner you are using doesnít melt the plastic.
I tend to use cellulose thinners, or mentholated sprit. Mentholated sprit can be used on most plastics as it has no effect on them. Once clean make sure the cleaner has dried or evaporated right up before starting, as if you hit a wet patch the paint will react, and leave a mark.
The next thing to do is spray the item with primer. You need to shake the cans well, as they tend to settle in the shops or while not being used, and the paint sediment and thinners needs mixing well prior to spraying.
A tale tale sign of not shaking enough is when the surface of the paint crinkles. This is because the can was not shaken enough, and sudden you have sprayed using a pocket of thinners not mixed well with the paint, and itís attacked the surface. If this happens its game over. You need to then let it dry and sand flat and start again.
So apply two coats, depending on what the item is to how heavy a coat can be applied. If flat like this you can apply a heavy coat as it wonít run, but on curved or vertical surfaces its better to apply several thinner coats instead of one heavy one.
Once the paint is dry, sand the surface with 2000 grade wet and dry, and wipe clean. You can see from the picture the sanded side and the just left side.
Its seems a misconception when painting stuff is that the sanded side looks far rougher in finish than the un-sanded side, which puts people off sanding it. Once sanded the surface colour is uneven and people prefer for some daft reason to not sand it and have a nice even colour. It looks good to start with but shows up later.
Spray two more coats of primer and sand them ready for the coat of black.
Now apply two coats of matt black and let dry, then sand the same as the primer coat. Always use a separate piece of sandpaper when sanding different colour paints, especially when using wet and dry to avoid leaving paint coloured powder behind.
At this stage again people watching it being done, always point out the un-sanded side looks so much better than the blotchy sanded side. To be honest it will till the lacquer is applied and the surface polished, which for some reason people find hard to understand till they see it.
The problem is un-sanded side looks ok to most people who havenít ever sanded between coats, but once they see the finish obtainable with just a small amount of extra work, most are converted.
With the black applied and sanded flat, its time to apply the clear gloss lacquer. This needs to be done in cooler surrounds, not in direct sunlight or a hot room. While the under coats are sanded flat so applying the those coats is not that critical, but applying the gloss coat requires the entire surface to be covered without it starting to go tacky or you get huge amounts of overspray.
I always spray at around a 30 degree angle to the piece being painted and work from the bottom up, that way any overspray is on the to be painted section, not on the section just painted. If you start from the top and work down, the overspray is landing on the already painted area, and if it does start to go tacky, its again overspray which shows as tiny spots. While this is not critical as it will be sanded back, its preferable to get this coat as smooth and even as you can before its sanded, to minimise work.
As you can see from the picture below, the two sides are now visibly different. The one on the right wasnít touched, and the one on the left was sanded between coats.
Unless you spray in a clean room with filters, you are going to get bits stuck to the surface, its unavoidable as its dust in the air. With the un-sanded side these will show up when finished, but as the sanded side now has to be lightly sanded again and polished, the surface will be free of specs when done.
So to finish this off its firstly left overnight to dry properly, then sanded very lightly with 2000 grade wet and dry using lots of water, then carefully dried off and polished with a fine automotive cutting compound. Remember the cutting compound will take the paint right off if you rub too long and hard, but we are only polishing the surface, so apply a small amount of cutting compound, then rub gently checking all the time how itís coming on.
As you can now see, the side that was sanded back between coats has come up almost mirror shiny compared with the untouched side. You also need to remember over several days the paint will harden thoroughly, meaning any imperfections will become more apparent.While on some things this really doesnít matter, but if youíre spraying a costume related item like Darth Vaderís helmet, a super shiny deep gloss black finish is preferable to the standard can finish.
You can also make the paint look deeper by lightly sanding and apply more coats of lacquer, but each time a coat is applied it softens the coat underneath and takes longer to dry. So allow at least a day between applying coats of lacquer and several days before you use cutting compound on it.
In conclusion you can get good results using a can of paint, but it requires more work. Cans are inherently inconsistent as the nozzle is an injection moulded non precession part. Also the first time you use the can it will spray better than once put to one side and stored. Even inverting the can to clean the pipes out inside, and taking the nozzle off and washing in thinners, the results the second time and normally visible poorer than the first time.
My recommendation would be buy a cheap airbrush and run it off canned air, only what about the paint. Well I canít advise you to do this, but I use a cheap modelling airbrush, and still buy cans of paint, as itís easier, but remove the paint from the can and pour it into the glass jar of the airbrush. The results of doing it this way are noticeable mainly as the airbrush sprays the paint on in a much finer mist so it covers better.
So cans are ok, but donít except a perfect finish straight from the can.