Originally Posted by WebDog
I would just rough it up with like a 40 grit before putting another layer on the outside if that's the route you wanted to go. You will have to give the glass and resin something to bond to.
Or...another and possibly a better option is to go with the kitty hair on the inside. This stuff can be a little tricky how ever. If you don't mix it throughly (as with regular bondo) you will have soft spots, no good. It's somewhat difficult to mix since the strands in kitty hair are so long. Another downfall is that when you go to put it on from the inside you might end up getting air pockets and not know it. That can cause cracking since it's a void.
I would recomend going with DuraGlass. It's just as good and easier to work with. The strands are a little more fine so it will be easier to mix. It's still EXTREMELY strong once it's kicked. I used about 2 gallons of it on my box, but my box also has about 8 sq. ft. (3' w x 2.5' l) of surface area where I had to put the stuff and I was using it ONLY. No fiberglass mat here. It's fairly expensive and can only be had at an auto body supply store (I paid about $35 a gallon for it). It's completely water proof and extremely strong.....
just a thought!