It's totally possible. If it's not happening then there's a problem with the sanding technique. What you need to be doing is sanding down the high spots while filling in the low with new epoxy. That's how you get a uniform gray surface. The most likely explanation for it not happening is that you're not holding the sander at a constant angle relative to the surface and you're following the hills and valleys up and down instead of just slicing off the hilltops. Another possibility is that you're applying the subsequent coats of epoxy evenly instead of preferentially to the low spots.

If you're going to paint anyway, I'd say switch to a fairing compound to fill the weave and use a longboard to sand it by hand. Fairing compounds are easy to sand, hand sanding goes as quickly as power sanding epoxy. The longboard will give excellent results.

Good luck,

Laszlo

   Thanks, it likely is a technique issue. After the last few coats of epoxy, I used a plastic scraper, thinking it would clear epoxy off the highs and leave it n the lows. Still, sanding yields lots of shiny spots if I don't grind what feels like way too hard. 

Isn't fairing compound for wood?

Hi Jim,

a couple resources on the CLC site that appear relevent to your question and may be useful if you had not already seen them:   

https://www.clcboats.com/shoptips/epoxy_and_fiberglass/fiberglass_weave_epoxy.html

https://www.clcboats.com/shoptips/building-stitch-and-glue-kayak/sanding-varnish-preparation-stitch-and-glue-kayak-video.html

on the fairing compound question, lazlo is referring to an expoxy based fairing compound which works fine on boats.  its similar to bondo used on automobiles but can be made with the epoxy you have and adding micro-baloons:  https://www.clcboats.com/shop/products/boat-building-supplies-epoxy-fiberglass-plywood/phenolic-micro-balloons.html

you make up a paste of this and use a plastic spreader: https://www.clcboats.com/shop/products/boat-building-supplies-epoxy-fiberglass-plywood/plastic-epoxy-spreader.html    to push the material in the low spots....and then sand..   it is relatively easy to fill the weave with this material and it sands easily.   but as lazlo said, not to be used unless you expect to paint the boat becuase the material is not clear.

hope that helps

h

   I agree, if you are going to paint, the micro balloon filler  added to the epoxy is the trick. But be sure to sand those shiny low spots first so you get a good bond. For that I just use a small piece of sandpaper and my fingertip. I applied the epoxy with a flexible spreader. I found the CLC ones a bit stiff and used ones I picked at my local Woodcraft. I had to go through two or three rounds of fairing but each time the problem areas got smaller and fewer. I used an orbital sander with 120 and 220 grit. 

   Thanks All.

Will MAS Cell-O-Fill accomplish the same thing as micro-balloons? I only ask because I have some.

   No. It has to be microbaloons. Using cell-o-fill will not work and is incredibly difficult to sand H

  " After several rounds of sanding with a 120-grit orbital, I STILL have a surface with almost as many shiny spots as gray."

I get that when sanding with a filled up, used up disc of 120. More polishing than sanding.