The short answer to this is that yes you can use some automotive spray paints on plastic scale models.
Is there an advantage to using car spray paints?
The advantage of using car paints on your models is that they are available in a huge range of colours that are often matched to authentic manufacturers samples, allowing you to paint your car models with the most authentic colours. Also, given that they are designed for use on full size cars, they have a tough finish that makes them very resilient to handling and they can be polished to a high shine. However, care must be taken as the type of solvents used in some automotive spray paints as they may damage the plastic used in model kits, and this will have a disastrous effect on the final finish.
How do I use car spray paints?
Firstly the parts should be cleaned to ensure that they are free of grease, dust and finger prints.
Next a primer specifically designed for use on plastic should be applied in light coats to all the parts you intend to spray. Don’t forget to also prime the inside of the body. These primers are often found next to the colour spray paints but you should ensure that you are getting a compatible product. If required, this first coat of primer can then be rubbed down with a fine grade of abrasive to ensure a completely smooth surface before applying a second coat of primer. If you are unsure if the paints you have chosen are suitable it is a good idea to experiment on a spare piece of sprue.
The base layer of the top colour should be applied very thinly and is designed to give the next coat something to grip and should not be intended to completely cover the model. The top coats should be applied in even layers heavy enough to give good coverage but taking care not to go too heavy as this will cause excess paint to pool in corners and cause ‘runs’ in the paint. Each layer should also be given plenty of time to dry before the next layer is applied. The model should be put aside somewhere warm, dry, and dust free in order to fully cure. This is to allow all the solvent vapour to properly evaporate from the paint so that it doesn’t affect the subsequent paint coats.
Once a satisfactory finish has been achieved the model can be given a clear coat to protect the finish and give a suitable surface for any decals to be applied.