340 is probably too smooth.  You will want to roughen with 220 to make sure the new epoxy can physically adhere to the older.  For a good looking overlap: 1. Run a line of masking tape along the hull where you want to deck glass to stop.  2. Wet the glass out down to and over the masking tape.  3. When the epoxy is still green, use a SHARP razor knife to cut the deck glass along the masking tape.  4. Pull the tape off.  5. Sand the edge and skim coat epoxy to desired level.

   Thanks mark! That’s brilliant!! Exactly what I was looking for. And I’ll go rough it up again with 220. Like I said, I got carried away :-)

   This worked perfectly!!! I just laid the deck glass and I have a perfect line!!! CLC should add this to the instructions. I can’t imagine the mess if I’d tried to do it with cut glass cloth. You can even see the mess in their build video. 

Mark, I owe you many beers for saving me hours of sanding!!! If you’re ever in Tampa let me know! Thanks again!

When I figure out how to post pics I’ll add some of the results. 

   What kind of fiberglass is that where the cut edges don't fray? With the stuff I used there were loose threads pulling off all over the place.

It's the kind where the resin has partially cured. It's no longer tacky, but still flexible. That's called the "green" stage and Mark's reference to the epoxy being "still green" means that.

Here it is actually being torn way back when I did the same thing for my WD12. I used clear plastic packing tape which has less potential for the epoxy soaking through. You can see how cleanly the glass tears when all the fibers are held in place by the partially-cured resin.

Once the glass is torn off, just remove the tape and let the resin fully cure, as Mark said. Then a light touch with some sand paper and the seam is invisible. In the picture below the seam goes right through the duck logo around eye level.

Laszlo

Laszlo, I was referring to the first photo.The trimmed edges of the cloth prior to doing the epoxy are so clean. Mine was like your first photo where there's lots of loose threads.

Useful tips! Thanks for this thread!

   Snowbound, I used glass from CLC.  I certainly frays along the edge but you can minimize that by cutting very carefully with good shears.

   Now that I figured out how to post pics, here’s how mine came out:

Shoot! Now I'm going to have to build another kayak just to find out how many hours of sanding this tip will save me. My "Go Fund Me" page coming soon. ;-)