How to erase those body boo-boos with some paint blending work

[Editor's note: This article originally appeared in our May 2010 issue.]

If you’ve priced paint and bodywork lately, you know that good work does not come cheap. Five-figure paint jobs are getting more and more common. Coupled with the “might as wells” that go along with paint work (rubber, chrome, etc.), not only does the expense add up, but the time required can end up taking your car off the road for quite a while.

So, what’s the alternative? Save the existing paint work by spot-repairing areas that are no longer up to snuff. We can often bring a so-so car back to nice-car status with some spot repairs, perhaps a few renewed pieces of trim, and a good detail job. While this type of work won’t win you a trophy at Pebble Beach, it’s a great way to keep a good driver-level car looking nice.

Spot repairs can be handled at a body shop or at home using a variety of methods and tools. Body shops tend to be more interested in this kind of repair work than full paint jobs, so you may be able to get a pro to do it during some downtime. On the other hand, we’ve had good results at home using everything from spray cans and discount spray guns to professional-grade equipment. 

While the methods, tools and paint supplies can vary a bit depending on the type of paint on the car and the repair work needed, the overall process is about the same. Generally, the area in question is sanded back to bare metal so that the damage can be repaired, often with some body filler. (We’re assuming that no welding is required—that’s a topic for a different story). 

The paint around the repair area is then feather-edged to offer a smooth transition from the repair to the existing paint and bodywork. The area is primed, usually with a high build primer-surfacer, before being sanded smooth. The priming and sanding process may be repeated a few times until the repair area is straight and properly transitions into the existing paint. 

Finally, the topcoat—and possibly the clear coat—are applied, sometimes with a blending agent, depending on the type of paint being used. The area is then buffed. If done well, these types of repairs are very hard to spot.

We recently worked on a very nice 1978 MGB that still needed a bit of attention. A dogleg panel had been repaired years ago, but the paint was misapplied. It was blistering and peeling, a sore spot on an otherwise great-looking vehicle. The step-by-step process needed to renew this section of the car can be tackled by just about any DIY enthusiast.

Step 1:

Here’s our trouble spot. This MGB’s dogleg was repaired several years ago. While the panel was still good, the paint was starting to blister, putting a blemish on an otherwise beautiful car. We decided to spot-repair the finish, blending the paint into the quarter panel.

Step 2:

We sanded away the paint, primer and filler to bare metal using an air-powered dual-action sander fitted with a 36-grit disc. We also could have done this by hand or with an electric sander.

Step 3:

We tried to feather-edge the repair zone by sanding back the various layers of filler and paint with 220-grit paper. We found a bit of a ridge that we couldn’t sand smooth, so we used some catalyzed spot putty to make the transition. We applied it with a rubber squeegee and waited about 10 minutes for it to harden.

Step 4:

We then sanded the repair with 220-grit and then 400-grit paper. Once we got to the 400-grit paper, we sanded up into the color coat for about four inches to make sure the new paint would be able to bond to the surface.

We always make sure our paper is not dull. Fresh, sharp paper will quickly take off the high spots and make for smooth, straight bodywork. Dull paper tends to follow and exacerbate the highs and lows, making the bodywork look worse in many cases. 

Step 5:

As we prepared to prime and paint, we covered the whole car with sheet plastic. This step is less crucial with some paints, but we always find it to be an easy way to reduce cleanup time and eliminate any overspray.

Step 6:

Before masking things off, we very thoroughly cleaned the area to be painted with grease and wax remover. In this case, we used DuPont 3090 Prep-Sol. 

We then started our masking job, first outlining everything with 3/4-inch tape. We also masked off the insides of the door and its jamb to keep overspray out of those areas. It’s important to use automotive masking tape since it won’t inappropriately react to the paint and solvents.

Step 7:

In the past we’ve covered cars with newspaper, but for $30 to $75 you can get a proper masking paper machine. It automatically puts the tape on the paper. We masked off everything right next to our repair area. Note that we masked off our table, too, in order to have a clean spot to mix our paint. Putting masking paper on the table also makes cleanup very quick.

Step 8:

We had determined that the car wore acrylic enamel over the original paint. We consulted with our paint supplier, who said we could use traditional acrylic lacquer high-build primer underneath non-catalyzed acrylic enamel paint. This kept our costs down and made for simple mixing and cleanup. We mixed the DuPont Fill ’N Sand 131S primer with 3696 thinner in a 1:1 ratio.

Step 9:

Since this was such a small repair, we used an older DeVilbiss siphon-feed touch-up gun. These guns are becoming obsolete, as gravity feed guns are more popular. However, either type of gun can provide great results. We put on four thick, even  primer coats, waiting about 10 minutes between applications. 

Step 10:

We allowed the primer to dry overnight.

Step 11:

Then we wet sanded the area with 320- and 400-grit paper. Because we had done a good job on our prep work underneath, we could then immediately begin to apply our top coat. If we had found some imperfections, we would have fixed them with spot putty before spraying more primer.

Step 12:

We used Dupont Centari acrylic enamel paint for this job. We felt comfortable using the standard OEM color as opposed to a custom tint, so we had our supplier mix the paint according to the factory code. If we hadn’t known the paint code for this car, the supplier could have computer-matched the color and mixed a custom tint.

Although we mixed our primer to be on the thicker side for good buildup, we chose a different path for the paint. We started with about one part paint to one part 8022 reducer; we thinned out the blend a bit with each subsequent layer to achieve a good transition into the existing paint.

Step 13:

We started at the bottom with a thin first coat to get even coverage. We then worked our way up to the edge of the primer. Note that we didn’t worry about the fact that the first coat was a noticeably different shade—that’s just the result of the very thin coat. 

We followed this procedure for three coats, each time inching slightly higher into the existing paint work. Before our fourth and final coats, we thinned the paint quite a bit more, adding about 50 percent more reducer to each coat. These two extremely thin final coats let the new enamel “melt” into the underlying enamel. Keep in mind that other types of paint will have different blending procedures and methods. Consult with the instructions or a professional for the best method for the finish you’re facing.

Step 14:

With the final coat applied, we left the paint to dry and cleaned our painting equipment.

Step 15:

After the paint dried thoroughly, we lightly buffed it with 3M Perfect-It compound and a foam pad fitted on an electric buffer.

Step 16:

Cleaned up and finished, the repair is virtually undetectable and makes the MGB look great again.

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