A question that usually comes up when a car needs a re-spray of paint is should the owner have the car scraped to metal or not. Car owners are usually advised by shop owners to have it scraped because they say it will ensure a better finish. Well, that depends…
Yes, removing the existing paint and starting with bare metal would be a good start. How do you remove the existing paint? You can use a chemical stripper to remove the paint. But some chemical strippers are strong enough to harm the sheet metal. So besides washing it off, you would have to use a neutralizing agent to ensure that the chemical does not harm the metal, the primer and paint that will be applied next.
There are two ways of applying the stripper: by sections using a paint brush; or dipping the entire car body in several vats filled with chemicals. This will remove anything that is not metal- as in anything and everything in all the nooks and cranny. Even the ones that you can’t see. You would have to find a way to treat these areas to prevent corrosion.
The other method is media blasting. This method uses air carrying fine abrasive materials that can remove the paint when it hits the surface. You can use aluminum oxide, crushed wallnuts, plastic pellets or crushed dry ice. However, care should be taken when using the more abrasive media as heat generated can warp the sheet metal.
The other method is to use sandpaper and sand down the paint and primer. This method is time consuming but it gives you a feel of the body. It’s sort of like a Zen-like experience.
Now I may sound hesitant to agree that stripping the paint to bare metal is the way to go… here’s why. The best corrosion protection your car has is the original one from the factory. The sheet metal was treated in a process that pickles the metal and the primer adheres to the body perfectly. The body is charged so that the primer is attracted to the metal.
Now, if your car has no rust issues or does not need extensive body repair, sanding down the paint enough to see the primer will be just fine. Using a good epoxy primer will work fine. Now if there are rust issues, then that will have to be addressed.
Corrosion is the product of the metal reacting with the oxygen around it–rust or iron oxide in the case of steel. But you would need heat to help jumpstart the process. But rust is the natural protection of steel when left out in the elements. A layer of rust forms on the surface. As it gets deeper into the metal, it prevents the oxygen from penetrating deeper. So the corrosion process slows down.
What is the best way to protect steel from corrosion? Well, from what I learned from selling steel utility poles, one is sacrificial type protection and two, barrier type protection. Sacrificial type protection is when you use a material that would sacrifice itself. How? By giving off its electrons instead of the steel. Zinc is such a material. Galvanizing is the processes that lets zinc adhere to steel to help protect it.
Barrier protection is when you apply a coating or a barrier to protect it from the elements. Paint is such a thing. It prevents the elements from adhering to the metal surface.
If there are rust spots and it has not eaten through the metal, it can be sanded down and treated with a rust inhibitor or rust converter. This will chemically neutralize the rust. If a primer with zinc will be applied on the surface, that would help in preventing the development of rust later on.
Now, I am not saying to follow my lead or anything like that. There are cases wherein the need to scrape the paint down to bare metal is really the best solution. Prepping and using the right products can help ensure a good quality paint job. When you go around looking for a shop to paint your car, don’t be blinded by just the paint job. Yes, it looks shiny but what lies underneath may bite you later on.
See how they work. There are shops out there that will do a lot of short cuts just to make a quick buck. If they say that they will use a certain brand of paint, they might use or mix other brands to save a buck. Even the use of water and soap to clean the surface before painting can affect the outcome. Any oil left on the surface can affect the paint from adhering properly. A cleaning agent is used to remove any contaminants on the surface. Car show winner, yes. But I have seen cars in car shows on the final day of the show where the paint starts to bubble.