Hi Bill,

I have not dealt specifically with the problem you have, but here are my suggestions.

I very much doubt that the problem epoxy is in your cloth if only the final fill coat has the problem epoxy in it. The cloth would have been completely soaked and coated by good epoxy before you applied the final fill coat. The final fill coat could not have penetrated the glass. You may have bad epoxy in the low spots that were still present in earlier fill coat(s), but that does not mean that the bad epoxy actually penetrated the glass. That, I think, means that you may not have to remove any glass to cure your problem. It also means that this problem will not be capable of causing de-lamination either within your cloth layers or between the glass and the wood.

If the epoxy is still capable of being dissolved, it may be possible to remove it with vinegar and mild abrasion. If I were you, I would try one of those plastic pot scrubbers and white vinegar. If the vinegar will still dissolve the epoxy to some degree, the pot scrubber should dig into the hollows of the previous fill layer without removing any of the earlier fill coat. If this works, it would leave you with a clean epoxy surface which you could then gently sand to enhance adhesion, and then re-apply the final fill coat. Clean with clear water and allow to dry completely before final sanding and coating.

If the epoxy is too far gone to dissolve, your idea of scraping the faulty epoxy off would be worth trying. I would first try a plastic scraper that cannot dig into the earlier fill coat. If that doesn't do the job, try a relatively dull (but smooth, no nicks or hollows which would cause scratches) chisel at a low angle, and increase the sharpness as necessary to get into the bad epoxy without removing the good stuff. As you rightly expect, a low angle of attack is important to avoid digging into the good epoxy. However, a sharp chisel may dig in anyway, so start dull.

Once you get all you can off by scraping, you may have spots of bad epoxy in the hollows of the earlier fill coat. If the stuff will not dissolve, and is too hard to remove with the plastic scrubber, you are left with a dilemma. If you sand deeply enough to get it all off, you may get into the cloth, if you don't sand deeply enough, you will leave bad epoxy in the hollows. If it was me, I would try sanding further, but only until the earliest hint of hitting the glass appears, and then stop and re-coat at that point even if not absolutely all bad epoxy is removed yet. This would take careful monitoring under good light, and given the soft epoxy, probably a lot of gummed up sandpaper. You could try wet sanding to avoid gummed up paper, but I am not sure whether this could cause problems once you got to the glass.

If remaining spots of bad epoxy become visible later, you can always sand deeper into the glass then. In any case, it should not be necessary to remove the whole top layer of glass. You only need to get deep enough to get the last bit of bad epoxy in the hollows. Once that is done, you would be ready to put on another layer of glass and finish coat it.

If anyone's experience suggests this advice is poor, dissenting opinion is encouraged!

Good luck,

Allan Edie