My friend has just completed a stripbuild kayak and have experienced these white marks on the sides after sanding down ,-maybe in to the fiberglass. It will not dissapear when putting additional epoxy over the sanded areas. Anyone has any idea what this is, and why it happens ?
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RE: what are these ?
» Submitted by Laszlo - Fri, 8/15/08 » 6:18 AM
It's just what you say - sanding too deeply and getting into the fiberglass. Once it happens the choices are to live with it, paint or otherwise camouflage it or strip off the glass and start over.
It's caused by the sealed edges of the glass fibers being scuffed, sort of like those decorative pieces of frosted or engraved glass. Because they're sealed, new epoxy has no effect on it.
The way to avoid it is not to try to sand bumps down, but to build up the valleys around them.
Hope this helps,
Laszlo