The light weight spackle collapses a little after drying. It is challenging to make the final finish perfectly match with original surface. Here is my approach:
Material list:
- Polyurethane glue such as Gorilla glue (either brown or white, I normally use brown)
- small plastic piece slightly larger than target area, make sure medium flexibility
- masking tape
- paper towel for cleaning up
1. apply small amount of moisted glue
2. place the plastic piece over the target area, make sure this piece is just a little larger than the target area
3. use masking tape keep the plastic piece on the surface, waiting for curing. Keep an eye on the expanding glue under the plastic piece, clean away any protruding glue along the edges.
If the new surface is still not perfect, then either repeat the above procedure or fill with light weight spackle.
If the area is not too big to fix, and the model can handle a little gained weight, just regular spackle will do the job, giving you smoother and tougher finish.