I had a crack in my canopy and decided to fix it as well as I could using the weldon products. I drilled a hole using a plexi bit to stop the crack. I filled in the crack with the thinner weldon #3 and sanded it down so its smooth. I then filled the stop drill hole with #16. I checked it about an hour later and there were little spiderweb cracks emanating from the hole. I had no idea how they showed up. I drilled those out and just filled those holes with the 16 again. 10 minutes later more cracks showed up. I drilled a bunch of practice holes in some scrap and can't get any cracks to show up in the scrap pieces. Why is my canopy cracking when I put the weldon in the hole?