My mast took a hit and the leading edge was damaged along with the trailing edge. Im planning on filling the area with epoxy , mixed with some black pigment.
I was wondering if I should add some sort of filler to the epoxy to help with sanding? I’m worried about having trouble getting the repair faired/ sanded flat after the epoxy cures with out sanding the good sections of the mast.
Thinking of using packing tape around the epoxy to help get it flat ? Less sanding?
Packing tape to mask the area around the chip, then packing tape over the chip after applying epoxy should keep sanding to a minimum. Once cured, blue painters tape around the repair can protect the rest of the mast when using low grits to get it close. Key is to have a bunch of sandpaper grits and work through them patiently reapplying the protective blue painters tape when needed. Eventually it will be faired in close then do the final blend with really high grits.
Phenolic or glass micro balloons can be used as filler to make sanding easier, but the repair won’t be as strong.
Hysol 0151 is a good thixotropic epoxy that resists running. A thixotropic epoxy will be easier to get the right amount of epoxy in place before taping over the repair. Run a popsicle stick or something over it to remove excess, then tape over it to get the final shape. Make sure the backside of the tape is used when taping over it.
Some chopped glass or carbon mixed in would provide additional strength, but might leave a slightly fuzzy finish once sanded.
I would use clear packing tape on one side and around the leading edge to make something of a mold/dam. Then cut up a bunch of carbon into short fibers (could use glass) and mix in some 2 part epoxy. West Systems 105/205 is easy to get ahold of but lots of good options. You can pour it into the mold/dam and let it cure. You’ll only have to power sand one side, but it won’t take long if you have a halfway decent rotary sander and some 100grit.
Add silica to your mix to keep it from running too much, it also makes the repair a bit tougher than just resin.
For the sanding, you can use small fine metal files, make it much easier to not damage the area around the repair when removing most of the excess, then remove sanding marks with fine sandpaper.
Quick coat of matt clear acrylic spray will help blend it with the rest.
West 403 microfibers in the mix also, resin alone or resin with just microballoons with a ding that big is likely to crack/shatter if it takes another direct hit. I think the microfibers are worth the money over chopping your own, no fuzzy finish or voids to fill in after initial sanding.
I also use a razor blade as a plane to get the epoxy blob down close to the surrounding surface level. A bit of tape over the blade where it contacts the undamaged part will save you a bunch of small scratches until you get the technique down.
This is a non-structural area of the mast, for all masts, so you don’t need to worry about strength. You’re welcome to purchase a “mast repair service” on our site and we can fill it with the product we use to repair clients’ masts when they hit reefs/sea-life/etc. It’s a black, non-sag toughened epoxy. Mast repair is $100, but you can quickly spend that on adhesives, fillers, dispensing equipment… and your time. We’ve done this many times so it will be mint, just wanted to throw it out there. If not, as others suggest a black body filler with good masking should do the trick. No need to add carbon or structural reinforcements.
I trick I saw for sanding chubanga foils is to have tiny blocks of wood for sanding 15mmx 8mm - this keeps the sanding focused so it minimises changes in shape of the profile.
