Once dry, the spot putty is...
Once dry, the spot putty is wet sanded with 400 grit.
Once the flaw is filled and sanded, it can be touched up with paint. If the spot putty is smooth and sanded dead-level, usually no primer is necessary. Some distortion will be visible, but this will be filled by the paint and sanded-out once it dries. Larger repairs may need some surfacer to help achieve a perfect finish, but the painted area has to be extended over a larger area to cover the primer. Small touch-ups (chips and small gouges) can be done with an airbrush. We use a $5 unit from Harbor Freight Tools which works great. Larger repairs (panel blends) are handled with a touch-up gun. For small repairs, we like to over-reduce (double the normal reduction) the paint and use a slower than normal reducer. With this mix, use multiple light coats to color-up without excessive gluggy buildup. After it's colored-up, reduce it further (up to four times normal reduction) so that it almost sprays tinted solvents to blend-in the repair. Larger repairs use a more conventional mix, but thinned-down for blending, extending the repainted area.
Buff Dude
The final buffing should be done only after all the repairs are made. There are countless products on the market for buffing paint. After cutting, machine buffing is required to bring back the gloss. Use the professional bodyshop compounds made for machine polishing. 3M makes an excellent line of compounds for a variety of applications. The buff-out is a two-step process starting with a coarser cutting compound to remove the sanding scratches. Next, a polishing compound, called a finishing glaze, is used. The finishing glaze removes the swirl marks from the compounding step and gives a super high-gloss finish.
Buff with a dedicated buffing machine. Though it looks like a sander, it turns the slower rpm (1500-2000 rpm) necessary to reduce the chances of burning the paint. Paint buffers are rotary, not the orbital machines sold for Saturday wax jobs. Quality buffing pads are a necessity, and are usually made from wool. Two types of pads are required: a coarse cutting pad for the compounding and a fine polishing pad for the final finishing glaze. Foam final finish pads are available, but we prefer wool.
The compound usually has instructions on applying the sauce, but handling the machine correctly takes skill and experience. Avoid using too much pressure and let the compound do the work. The main danger is catching an edge that can burn through the paint in an instant. When buffing, hold the machine at a slight angle, so only one side of the pad works the surface at any given time. Pay attention to the direction the pad is rotating and make sure it always rotates off the edge or body line rather than into it. In areas such as around doors, the hood, or trunk, slightly open the piece to raise the edge so the pad can ski over it without going directly into the edge of the adjacent panel. Where it's not possible to rotate off the edge, orient the buffer so the outside of the pad wipes over in line with the edge.
After a while the pad begins to load up with dried compound and needs to be spurred periodically to keep the surface clear of buildup. Turn it on and run the point of a screwdriver it across the surface of the pad. When switching from the cutting sauce to the polishing formula, thoroughly wash the car to remove the remnants and dust from the cutting compound. Particles are picked up by the polishing pad, introducing them into the fine polishing operation. Buffing slings compound all over, and if it's allowed to dry, it will adhere to the paint. Always clean the jambs, glass, and other areas while it's fresh, using plain soap and water.
A coat of primer-surfacer...
A coat of primer-surfacer is next, followed by a wet sanding with 600 grit. That's the extent of the prep in this area.
The back of this quarter has...
The back of this quarter has plastic filler, and it's cracked. When the car is restored it'll get metal, but for now, we'll patch it up.
Ground, refilled, spot puttied,...
Ground, refilled, spot puttied, and sanded, the next step is primer surfacer and the final sanding.
These small flaws are painted...
These small flaws are painted with an air brush, using many coats of very thin paint.
We had a deep gouge on the...
We had a deep gouge on the driver's door. Because of the size of the flaw, we airbrush some primer over this area for a smoother fill than the spot putty alone can provide. The area needing paint to color the primer spot is now much larger than the original scratch.
A relatively wet mix of paint...
A relatively wet mix of paint is stirred into a touch-up gun, and the repaired area on the door edge is painted. The panel isn't masked, we just use some wide tape around the jambs. Each successive coat gets more reducer, and the painted area is extended.