It isn’t uncommon to expose dry fibers in your part while you are sanding or trimming. You might even find dry patches in your vacuum infused part, too. This results from an improper infusion, or wet-out, or resin that has not fully cured. Depending on the location and intensity, this can be simple to address.
If you have the time and means, post-curing your part in an oven or a dry space is the first step to take. Most resins require this to fully set up, meaning your part needs some time in the oven to bake, or 4-7 days at room temperature. When your part is fully cured, you should have no trouble cutting it cleanly. Resins that are not cully cured will act “gummy” when cut with an abrasive tool and quickly clog up your grinding disks and cutting wheels.
To remove stubborn dry fibers on a trimmed edge, orient your 90 degree die grinder disc to shear the fibers off your part using the edge of your sanding disc that is moving toward the part. If one smooth pass down the length of your cut doesn’t remove the fibers, follow-up with a corresponding pass moving in the opposite direction.
Using a flat hard block, sand perpendicular to the edge of the part to shear the frayed fibers at the base. This will leave you with a clean edge which can be prepped for clear coat.
A final suggestion for dealing with dry fibers is to paint on resin to the dry material. After curing to a good tack, you can drag your safety razor along the base of the fibers to remove them. Allow to fully cure, preferably in an oven at ~120 degrees F, and then proceed with sanding and grinding as necessary.
These steps will help you correctly address areas of dry carbon in your parts, whether they have been produced via infusion or through wet lay-up. As always, if you have run into dry carbon in your infused or laid-up parts and have your own successful solutions to share, send them to us through the comment field below (make sure to include your email) and we will share your questions and advice in our troubleshooting posts. Remember to check our other DIY Blogs as well for resources and expertise throughout your carbon fiber journey. Good luck!