I have an Annapolis Wherry project which I have been working on since last year when I finsihed class. The 4 center-most panels of the interior still have some fiberglass weave showing. Apparently, I applied only two coats of epoxy to the weave during class, and have been working on other aspects of the boat (very slowly) since. Not sure why I stopped at two coats, but here I am trying to figure out how to proceed.
The exterior glass weave is completely filled.
I understand that in order for an additional coat of epoxy to bond to existing epoxy, sanding is required to provide a way for the epoxy to bond mechanically as opposed to chemically since the existing epoxy was applied long ago.
However sanding into the weave does not seem advisable.
Will two coats of epoxy on the interior glass be sufficient?
Can I "rough up" the existing epoxy with a scotch-brite type of cloth without damaging the glass?
Any other creative solutions?
I had one project where I filled the weave after a 6-year hiatus, so you'll be OK. The single most important thing is to completely clean the old epoxy. Get all the dust, dirt, grease, mouse pee, bird lime, etc. off the old surface (a Carolina Wren snuck into my garage through an unkown crack and made a nest in the rafters as a result of which she "blessed" my boat).
Once the surface is completely clean, you can actually proceed without sanding. Epoxy will happliy bond to itself without needing to be roughed up as long as the surface is free of contamination. That difference between the so-called chemical and mechanical bonds is more of a thing for polyester resins, not epoxies.
But, if you don't feel comfortable doing that way or if you can't achieve the requisite cleanliness any other way, you can sand/rough-up the surface exactly as you describe. A Scotch Brite pad or #220 or finer paper will do what's needed.
And you are absolutely correct - you do not want to sand into the weave. You just want to roughen the surface of the epoxy that is saturating the glass.
Finally, if this is truly on the inside in an enclosed space where you won't be trying to sit on it, you don't actually need to fill the weave.
Laszlo
Cant thank you enough for the quick reply. I will defintely skip filling the weave now!
Also, I was unaware of the distinction between polyester resins and epoxies. You mention epoxy will bond to itself if the surface is free of contamination, but what about paint. My next step will be to finish with paint: interlux perfection. I was assuming I would need to rough up the surface before applying the first coat. Is that true?
Yes, Interlux Perfection is a different chemistry than epoxy.