ORIGINAL: gow589

Wallering is the result of part of the surface being harder than the other. This could be epoxy glue joints, where hard wood meets balsa, or even harder sections of balsa. It doesn't matter if you are using a block. This came really aparrent when I was block sanding my car for paint. As soon as I hit metal, sanding stopped. If I continued to block sand, it would still "waller" (if you can come up with a better term let me know). With a sharp 60 grit paper it cuts through harder areas such as wood and epoxy glue joints without creating low spots. It is much easier to come up with a final shape.