Spray Painting

Mixing the paint is actually important

Definitely take the time to shake the can properly. The ball bearing in the bottom needs time to properly mix the paint and loosen it up from the bottom of the can where it has settled. Follow the instructions on the can - if it says five minutes it actually needs five full minutes of shaking.

Surface preparation matters

Whether you are using a primer (see below) or not the quality of your surface preparation matters. Surfaces to be painted must be absolutely clean, degreased, and dry. Debur edges to stop paint building up on corners. Consider scuffing the surface with a scotchbrite pad to aid adhesion.

Avoid heavy coats of paint

Multiple light coats will always give a better result than one or two thick, heavy coats. Build each layer up gradually - don't worry if the first few layers look patchy and uneven as it will soon fill in.

Start and finish each pass off the material

Point the nozzle just off to the side of the surface you are painting, and start painting. Move smoothly all the way across the surface, past the end of the area you are painting, and then release the nozzle. Move down slightly to achieve a satisfactory overlap and then continue.

Stopping and starting paint application pointed at the surface you are painting will give you runs and sags. If this will cause problems with overspray you need to mask off areas you don't want painting.

Overlap each pass slightly

As you are painting back and forth across your part you should overlap the previous pass slightly to build up an even coverage.

Don't spray too close

If you try to paint too close to the surface you will deposit too much paint in one location. If you are getting runs or sags move the nozzle a bit further away from the surface.

Don't spray too far away

Spraying too far away means the paint is too dry by the time it is reaching the surface, which can result an an uneven "orange peel" effect. More paint will also be wasted as overspray, and it will take longer to apply enough coats to get a satisfactory finish because each layer will be thinner.

Mask off anything you don't want painting

Overspray is a big issue with spray paint - if you don't want paint on a particular surface you need to mask it. Masking tape works fine for small areas, but you'll need to acquire in sheets of newspaper or similar to start covering up larger areas.

Overspray will also paint things you're not even intending on painting - like your phone or glasses - if they are in the wrong position. Watch out for other people's work hanging in the spray area, too.

Primer for excellent quality finishes, and weird materials

Not all paint will stick to all materials. Sometimes you need to have a primer paint in between which has good adhesion to particular surfaces. This is especially important when it comes to plastics and metals like Aluminium - always use a good quality primer.

Primer will also help improve the finish of your painting. Spray a few coats of primer, then sand it back with wet & dry sand paper to smooth out and lumps and bumps. Repeat a few times for the best results.

If you're covering a strong material - perhaps a very vibrant 3D printed material - you will find that primer will help cover over the bright colours and give the final finish paint the best opportunity. For 3D printing in particular a "high build" primer can help fill in and cover over layer lines.

Clean the nozzle when you're done

Keep the spray paint usable for the next person - clean the nozzle by turning the can up side down and spraying a short burst of just propellant. This clears remaining paint from the nozzle and reduces the chance it will clog up.