Sanding a filler repair invisibly: feathering the edges

The filler repair has to form one plane with the surface next to it. Shape it with P80 on a long, hard block or on the random orbital sander with a hard backing pad – working beyond the repair, never just on it. A soft pad or your hand follows the bump instead of sanding it away.

Apply guide coat: wherever it stays, there’s a hollow that needs filling again.

With P120 and P180, feather the transition from filler to old paint out flat – the wider it is, the less you’ll see it. Run your hand across it with your eyes closed: an edge you can feel is an edge you’ll see in the paint later.

Use P240 to remove the scratches from the previous steps and key the old paint all around. Then apply primer surfacer: it fills the fine scratches and pores in the filler. Without primer surfacer, filler repairs often show through weeks later as the paint sinks.