The fingernail test
Robert's quickest way to judge a scratch takes about two seconds and needs nothing but your hand.
Clean the area so you're not grinding dirt into the paint. Then run a fingernail gently across the scratch, not along it. If your nail glides over, the scratch is shallow. If it catches in the groove, it's deeper. On a long scratch, try a few spots, since the depth can change along its length.
“If it catches your fingernail, nine out of ten times it will not buff out. All I can do is hide it.”
What the fingernail test measures: scratch depth
Car paint is built in layers. On top is a clear coat, a transparent protective layer. Under it is the base coat that gives the color, then primer, then the plastic or metal of the panel.
Most light scratches only mark the clear coat. Those tend to look white or hazy and your nail barely notices them. Once a scratch cuts through the clear into the color, or down to primer or bare material, it has a real edge, and that's what catches your nail.
Buffing out light scratches
Buffing uses a polishing compound to remove a very thin layer of clear coat, levelling the surface down to the bottom of a shallow scratch so it stops catching light. When the scratch lives entirely in the clear coat, it can disappear.
Buffing is one of the smaller jobs Robert does. See scratch repair for the service.
Touching up and hiding deeper scratches
A scratch that catches your nail is too deep to level without cutting through too much paint. Instead, it can be filled with color-matched paint so it blends in. Robert mixes that paint on site to match your car.
It's worth being clear about what this does. A touched-up deep scratch is hidden, not erased. From a normal distance it should be hard to find, but if you know exactly where it was and look closely in raking light, you may still spot it. That's the honest version of nine out of ten.
Key scratches that need a full panel repaint
Key scratches are their own category. A deliberate scratch usually runs across most of a panel, sometimes several, and is deep enough that the fix is sanding and painting the entire panel.
That's more than mobile service can do well outdoors, so Robert sends those to a body shop. Cosmetic repair vs. body shop covers where that line sits.
“Key scratches are a little bit difficult because the entire panel has to be sanded and painted, which is a little bit too much for a mobile service.”
Scratches on a bumper
Many scratches on bumpers come with scuffing: a corner that met a post or a garage wall. Those are often handled as bumper repair, where the damaged area is repaired and refinished rather than buffed or dabbed. The bumper repair page covers that work.
Rock chips are different again. They're small, deep points rather than lines, and they're handled as paint chip repair.
Getting a scratch repair quote from photos
Do the fingernail test, then text Robert a photo. Take one shot of the whole panel and one closer shot at an angle, with light skimming across the scratch. That angle shows depth far better than a straight-on photo. The photo guide has more tips.
Common questions: Will my car scratch buff out? The fingernail test
My nail barely catches. Will it buff out?
Maybe. The fingernail test is a rule of thumb, not a guarantee. Send a photo at an angle in good light and Robert can tell you whether he'd buff it or touch it up.
Will a touched-up scratch be invisible?
It should be hard to find from a normal distance, but a deep scratch is hidden rather than erased. Up close in the right light, you may still be able to spot it.
Does buffing remove paint?
A little. Buffing levels the surface by taking off a very thin layer of clear coat. That's why it works on shallow scratches, and why it isn't the answer for deep ones: getting to the bottom of a deep scratch would take off too much.
Can Robert fix a key scratch?
Usually not. Key scratches typically need the whole panel sanded and painted, which is too big a job for mobile service. A body shop is the right place for that.
Written from Robert Crenshaw's own explanations of how he works. Nearly 30 years repairing bumpers, and 25 years running his own business.