Auto Body Refinishing Basics
By Michael Albee
I have received several emails lately asking me about fixing rust and refinishing a car. This article will include a basic overview of the procedures used to restore the surface of a vehicle and get it ready for new paint.
After you have determined the exact area that is in need of the repair, the area of the car should have any trim, decaling or other emblems removed.
Begin by thoroughly cleaning the surface with a soap and water wash and follow that with a wax and grease remover. This will remove any wax, grease or contamination that is on the old finish. This is one of the most overlooked steps in auto body repair and it causes the most aggravation when it comes time to spray the new paint on the vehicle.
Next, any adjacent panels or areas of the vehicle should be protected by using masking materials or a suitable cover to keep it from becoming involved in the refinishing project.
Rust and Panel Repair is the next step. If rust is present, the rusted metal needs to be replaced to stop the rust from spreading. In addition to removing the rusted metal, the area should then be sandblasted and corrosion coated with a “Weld-Through” type coating to insure that it has be completely eliminated. NOTE: Be sure to check all of the the bottom edges of the fenders, rockers and quarter panels. Also look at the seams where any two pieces of metal are joined and the insides of doors and the trunk lid. These are all big breading grounds for rust.
After the rust is removed, a patch can be made from 22-18 gauge metal and welded into place with a wire-feed welder or torch. If you are using a torch, BE CAREFUL! It doesn’t take much heat to warp the thin metals that are used in modern cars. It also doesn’t take much to set a car on fire either. IMPORTANT TIP: Always have a fire extinguisher on hand when welding or cutting on a car. It may just save you car (or your life)!!!
If body damage is present, the panel should be replaced when ever possible. If you choose to repair the damage, be sure that it is not rusty. If it is, you will be wasting a lot of time and effort if the rust is not removed before continuing.
There are many ways to repair a dented or crumpled panel. In every case, it is important to remove the dent in the opposite way that it was inflicted. By that I mean that you must pull the dent in the opposite direction that it was put into the panel. Any small imperfections in the metal surface can be corrected by using a quality body filler. When using a body filler such as fiberglass or putty, it is important to keep the thickness of the filler under 3/8″ when ever possible. This will keep it from cracking and falling off as it gets older or during sudden temperature changes. Putty should always be applied in thin multiple layers and sanded between coats to promote proper adhesion.
Once the putty has been applied, it must be sanded smooth. The more smooth it is, the less primer you will need to fill the scratches that are left in the putty. (After you price primer you will know why this is important). The final coating of putty should be sanded with 80 grit paper. This will assure ample adhesion for the primer.
After the panel has had all of the damage repaired, it ‘s time to begin sanding the remaining paint on that panel.
Since you just finished sanding the putty work with 80 grit, you can continue to feather the rough edges of the existing paint with that same paper. Keeping the paper a flat as possible, work your way around the repair area until the paint is smooth and you can not fell any rough edges or steps in the layers of old paint. Switching to 320 grit, repeat the sanding steps above. When the sanding is complete, you finish the panel by priming the repair area and any bare metal with a good quality primer. I suggest the use of a Urethane based primer. It offers the best coverage with maximum build and it is easy to use.
When delaminating (or top coat peeling) occurs, it is very important to remove ALL of the paint from that panel, clean and prep the metal and then prime it with a high quality primer.
The next step is to “Block” the primer to make sure you have a smooth and even surface to apply new paint to. Blocking the primer is done by using a piece of sandpaper (usually 400 grit) with a ridged or semi-ridged block in between the folds of sandpaper. This allows the sandpaper to glide over the top of the primer and sand off the high spots, leaving the low spots until last. Using a guide coat of a darker or lighter color will aid in revealing the low spots. If you can block the repair and you don’t have any “sand through” areas you are ready to proceed to the next step. If you sand through the primer or hit bare metal you will need to reapply the primer and block it until you don’t sand through.
After “blocking” the primer to be sure it is nice and smooth, it is almost ready for top coating. But first you need to sand the rest of the panel. Using 400 or 500 grit sandpaper, sand the panel until all of the gloss has been removed. It is best to use a semi-ridged block to make sure everything stays nice and smooth.
Once the sanding is completed, remove all of the masking and wash the panel or panels to be painted and the area around the repair to remove sanding dust and other contaminants. Blow the area dry and wipe the area to be sure that ALL moisture and dust has been removed. (Nothing is worse than a little drop of water trailing across your fresh paint … except a big chunk of dust or dirt landing on it).
Once you are sure you have a clean and dry surface, it’s time to mask off the repair area so you don’t get any over-spray on the adjacent panels of the car. This step is critical, so take your time and do a nice job. If you over-lap a piece of tape onto the surface you are painting, or if you don’t get the next panel covered properly, the job will look like crap. Once the tape is in place, cover the adjacent panels of the car with making paper and/or masking plastic. NOTE: DO NOT USE newspaper or household masking tape to mask a vehicle. Automotive paint will soak into the paper and tape and get onto the finish below. It also make it next to impossible to remove the tape.
Now you are ready to start applying the topcoat paint, RIGHT ?!?!?
OK, if you are doing this yourself, (In most cases I don’t advise this), you need a high quality paint gun, an automotive paint approved respirator, eye and skin protection, a very well lit and well ventilated shop or paint booth and some automotive painting experience. If you don’t have any automotive painting experience, find someone who does and make them stand next to you the first few times you paint something! they can be of great help and they can offer tips and support.
To apply the top coat, follow the paint manufacturers instructions.
Assuming that you didn’t get any runs, orange-peel or dirt in the paint, when the new paint has cured, remove the masking materials and re-assemble the car as needed.
Well, that was simple! Have fun!!!!!!