If you live in an area that gets yearly snow, it is likely that you will end up with some calcium stains and build-up on your car by the end of winter. While most calcium stains in households are a result of hard water, calcium stains on cars are usually caused by the salt (calcium chloride) that is put on the road to prevent the surface from icing. You can remove these stains fairly easily and without damaging your paint using a gentle household cleaner that you make yourself.
Pour the vinegar into the spray bottle. This will make it easier to apply to the deposits. There is no need to dilute the vinegar.
Treat the deposits with the vinegar. Spray them heavily with the vinegar, then cover the entire area with cellophane for 15 minutes. The vinegar will soften the calcium and make it easier to remove.
Scrub the calcium deposits with a damp cleaning rag. The rag should be wet, but not sodden. Use heavy pressure and firm, circular motions. As the calcium starts to come up, be sure to rinse out your rag regularly so that you do not scrape up your car with the chunks of calcium. You can also add more vinegar each time you rinse out the rag. Once you are unable to get any more calcium off the car paint, you can retreat with the vinegar and try again.
Wipe down the car with a clean, damp cloth. This will remove any remaining calcium residue and the vinegar. Now your car is ready for a good cleaning and polish after its long winter.
You can add lemon juice to the mix if your calcium stains prove stubborn. Do not use abrasives to get the calcium off. However, you can scrub with salt, which should melt rather than scratch the paint.
Test all cleaning methods on a small, unnoticeable spot on your car before you use them on a wide scale.