I put my elbow through the bottom of my board. The ding was 2" by 3" and about 1/2" deep. The nose and tail had a few other dings from a road trip I had gone on.
My plan was to fill the hole with q-cell foam then put a layer of fiberglass cloth.
Something to keep in mind is how you want the patch to look. This board is an old beater it has been patched more than a few times, so color matching wasn't super important to me.
Step 1: Materials
knife/ box cutter
Resin (sun cure)
Step 2: Get to Work
Start by prepping the ding. Grab some rough sandpaper 80-100 grit then sand any of the damaged area. The resin needs a rough area to bond with and splinters in the old glass will leave air pockets.
Step 3: Mix It Up
Mix the Q-cell powder with the resin. You want the consistency thick (somewhere between toothpaste and play dough). When mixing or applying the resin It works best to do it in a closed garage or another place that doesn't have a lot of UV light coming in (make sure where ever you are working has good ventilation).
Step 4: Put It on
The resin I was using is UV activated, so you can only put this stuff on around a 1/4" at a time. Let is sit for 5 min in the sun and it will cure it. Put on as many layers as you need then sand it down smooth.
Step 5: Make It Smooth
You want to sand the new foam to be flush with the rest of the board.
Step 6: Color Match the Repair
I used the mix stick to try a few different shades of yellow. I ended up using a old yellow sharpie on the new foam.
Step 7: Lay Out the New Cloth
After the the foam is sanded down lay cloth on and cut it to size. I usually cut it so there is 3/4 of an inch over the edge of the patched area.
Step 8: Cover the Repair
Put some resin down and spread it around then lay the cloth on top of it. Spread it around and make sure there are no air bubbles. Add more resin on top and spread it evenly. Then sand it smooth. Make sure you don't go to deep and weaken the fiberglass you just put on.
I usually will put a second layer of resin then light sand it with 200 grit.
If it still isn't smooth repeat till it is.
Finally wet sand it with 400 grit.
Step 9: Have Fun With It
If you don't want to color match it have fun.
I just grabbed this stencil on google, I felt like the best way to cover a big white patch was a big white storm trooper helmet.
Let me know if you have any questions or have any tips.