How much sanding before glassing?

Submitted byneurichmond onSun, 04/14/2019 - 16:04

I am wondering how much sanding needs to be done before fiberglass goes on the hull?  I have some areas that are not really drips but where the epoxy has run some so that it is thicker in these areas (not a lot but is visible from a side view).  Will these areas be covered and hidden after fiberglass and epoxy coats are laid down or do I need to deal with these before I get to that step?


Not really getting your question - - you have runs before glassing the hull ?

Runs need to be removed - - sooner or later. Also, much easier to apply glass if you have epoxy sealed the wood and lightly sanded before the glass. If you add a little wood flour to the sealing epoxy it will fill any small cracks between strips you may have.

A good scraper is much better for me on making runs disappear. In fact I have started scraping the whole boat after fill coats to knock down all the high spots. Much easier than sanding and makes sanding much easier :)

Thanks!  These are just areas where the epoxy is a little thicker, not really runs but I think scraping is probably a good idea.  There is one coat of epoxy seal and these areas are where I was a little careless in how thick I put it on I believe.  Any suggestions for a scraper would be appreciated.  I have a paint scraper with replaceable blades.  Would this be an option?


I have tried several paint scraper types, even the curved ones I use inside the hull. The straight ones dig in at the corners, the curved ones only scrape a very limited area. The scraper I like best for epoxy is the retractable single edge razor blade type. I can put the blade in my vice and, using my scraper burnisher, put a nice scraping edge on it.

I think if you have runs in your seal coat that you are applying way to much epoxy. Just takes a light coat, just enough to see the wood change color. When dry lightly hit it with 220 sandpaper. This makes a snag free surface for the glass to slide smoothly over.


Tue, 04/16/2019 - 19:00

If its on the deck, its understandable that you might want to level it a bit. On the underside of the hull is a different story. Either way, just be careful to not sand or scrape deep into the wood.  Usually when you seal the wood, only a light sanding with 150 is all that's needed. Just enough to roughen the surface. Watch out for blush too. You can wash it lightly with some water and paper towels to clean it as well. If you can pull your finger on the epoxy coated surface and get a trail in the gloss, that's blush.