How to Paint interior parts
First take off pieces you are painting, if they can't come out, then it will really be a pain, you'll have to mask off the inside of your car and paint them while they are inside the car. If your dash or parts are slightly pliable or soft, then use vinyl paint.
Take the pieces and wash them with soap and water, use dish soap detergent..this stuff is powerful and will strip away wax, and grease and stuff.
Next, gently sand the parts with 600grit aluminum oxide sandpaper to rough them up a bit..be gentle, no need to use lots of force, if the parts have been coated with armour-all...or any products like that, then this step is especially important. ANOTHER option, and one that most bodyshops swear by are ScotchBrite pads, you need the dark-reddish brown scotch-brite pads (autobody grade), use these to scuff up the surfaces real well, you can find these at autoparts/hardware stores in the paint sections or by the sandpapers.
Next you have to clean the parts of fingergrease and dust, etc, ideally you should go and buy a liquid solvent designed to remove grease and dirt, this is used by bodyshops..you can buy at paint supply places, and better hardware/autoparts stores.
However?for smaller parts, isopropyl alcohol should suffice, now wipe the parts down with the alcohol real well and let the parts air dry.
Spraying paint directly onto plastic is sometimes not good enough, a step many people skip is the primering process. Plastic needs a plastic primer to ensure your painted interior parts will stay that way for a long time, and help the paint adhere to the surface. Don't use a grey, autobody primer, use a plastic primer which usually sprays on clear,
In a well ventilated and preferably warm environment, 70deg F , spray on adhesion promoter following directions on can (steps vary, some say spray on the adhesion then spray a coat of paint while it's still wet, others say wait till it dries)
What type of paint?
Remember, there are different types of paint - some are enamel-based, others are laquer based, others are latex based. You want to use the same paint and clearcoat and not mix and match different paint types, or you can get very poor results. Soft, or vinyl-like surfaces need a flexible latex paint or dye, automotive paint will not work well on these applications..they will chip and flake off. Harder plastics commonly used in car interiors, such as ABS plastic can be painted with standard auto base paint and clearcoat.
A 'paint system' is always an trouble-free way to go. This is a family of paint products all designed to work with each other, usually it includes latex or auto base paints, plastic and regular primers, clearcoats, etc all together. SEM is a popular example of a paint system. Ask questions, try to find a autoparts place that has a dedicated paint counter, ask them questions and you will get good advice for your customizing projects.
For all interior painting a FLEXIBLE clearcoat should be used if possible..this has a flex agent in it and will help keep the paint from flaking..this is especially important for areas that are hard plastic BUT subject to slight bending/pressure (soft plastic/vinyl should never be painted with auto base paint).
In conclusion, if you have used a product such as 'armour all' on your interior parts, a product called a 'fisheye remover' may need to be added to the paint and be necessary to prevent the paint from 'fisheying' or 'orange peeling'? if you've ever painted something and had it bubble up, that is what I am talking about..the pores of the paint cannot breath due to the oily armour all product fisheye remover can prevent this. Even after taking all the above steps, when painting my Sunfire dash, I had this problem, when the product was added to the paint, the problem was gone.
Once dry, position parts for maximum spray, sometimes you might want to prop them up on top of something to make sure you get good coverage..and apply a thin coat on all the parts from a good distance. Don't spray too close to the parts and use short, overlapping strokes from side to side. Overapplication will result in running, uneven coating. The key is to apply lots of light coats slowly building up the paint, not trying to coat everything in one or 2 coats.
Before you apply the final coat, use a floresent work light, or make sure the parts are under strong light... you'd be suprised upon closer inspection areas you miss, and corners that need more paint, etc.... sometimes to get a good coat around corners, it may be necessary to turn parts over once dry and do a coat around the edges with the part upside down.
Once parts have dried for at least an hour or two, or overnight, apply clearcoat to non-vinyl painted parts, clearcoat, unless specially designed... isn't usually meant for vinyl painted parts, you could apply some armour-all to shine up the vinyl parts after they have been dry for a few days. Clearcoat will help protect the paint from scratches/scuffs, etc.
P.S. I also buy a 'tacking cloth' it's a sticky cloth and it's used to wipe down the parts in between coats to remove dust and lint that settles on the paint...get it from paint shops, or the hardware/autoparts paint section.
Take your time and don't rush and try and paint everything in a day!
These are some steps I have learned through trial and error and through having close contact with a bodyshop?they have worked well for me, hopefully they work well for you too! Taking the time and following steps insures a longlasting and durable paint
Job for whatever your paint project is.