Yep, you must put a thin layer of glass over the top. I have two boats with magnets that I have had to retrofit with glass, and it solved the problem of rusting magents very nicely. The problem is caused by the magnets being so very strong. So strong they pick up sand and bits of gravel. When those bits sit between the hatch and supporting lip, they quickly grind a small perforation in the epoxy seal if there is no glass.

Ted

: I have a quick question.

: I am using magnets on my hatches and I have read several threads about
: glassing over the magnets. Is that necessary?

: I used a forstner bit to countersink the magnets and I will cover with a thin
: layer of epoxy, and then the WP-LPU that I am using to finish the hull.

: Is the epoxy and LPU enough protection of is the glass needed? I can't see
: that there should be too much wear and tear on the magnets, and the closer
: they fit the stronger the hatch closing.