Dallasb84

How to fix yellow or peeling gel coat carbon body panels.

Difficulty: medium

Tools: squeegee, 3" bristle brush, palm sander, 80,180,220,320,600,1000, acetone, wax and grease remover, water, shop rags, nitrile gloves, and a particle respirator or dust mask.

Material: high solids aliphatic epoxy

Background:

In this how to I will go over how easy it is to repair your carbon goodies. When your carbon first shows it is oxidizing you must take it in to get refinished or painted right away. If not you may find yourself paying out the butt to get it fixed.

Instead of following this how to, you do have the option of getting it painted when it starts looking like crap but, if the shop you take it to does not sand it to carbon and then coat it, it is more than likely to fail again and wind up at the dump.

When the gel coat begins to peel, turn yellow, blister or delaminates two things have happened. Uv has damaged the binding matrix between the resin and gel coat and the linking mechanical bond had been destroyed. Resin chemistry is like this. Exposure to uv rays is like a time delayed reaction once it has exposure the seconds minute hours and days it is exposed it continues to degrade. It is the nature of the beast. There are ways to slow it down but most all polyester, vinyl esters and epoxy resins are susceptible to uv. Luckily you can fix it.

Getting started.

I picked this damaged hood up for next to nothing as it shows major gel coat delamination, yellowing and peeling.



I removed the hood pins and got started by first sanding with 80 grit with a palm sander. I take each coating off the whole surface and continue cutting with 80 grit until I have found the composites laminate resin interface below the gel coat. This must be removed to get rid if the yellowing.

Shown here is basically the three coatings. You can see numerous layers of white clear coat, then gel coat then the resin boundary. Like I said before I remove all at once then cut the next layer. It is not needed to keep the sander flat. You can cut on a slight degree with the edge if the sander to speed things up and remove material accurately.


Just to reiterate, your goal is the remove all clear coat, gel coat and curt just into the laminates resin... Be very careful not to cut into the carbon fiber. It is easy to burn through... Especially at the edges. If you burn through apply a small bit of black paint or sharpie marker to hide the fiberglass. It happens but ... It's kinda hard to do if you are careful.

Notice in this photo the gel coat has peeled away.... Under that gelcoat is the resin interface... That what you just barely want to bust through to get to the carbon. That and the gel coat are what yellows and gets damaged by uv.... Not the clear.



So when you are where you want to be the hood will be at 80 grit. Wipe the thing down with water and a rag. You will see the carbon while it is wet and be able to find any areas you have missed.



Slightly going into the carbon at this point is no big deal... Just remember, white sanding dust is ok... Black is bad.

Now quickly start going over the panel with 180 twice, then 220 twice, and so in until you are to 320.... Twice. Wipe with a damp cloth.



Soak a shop towel with acetone and wipe once all over. Then do it again. The. Wipe with wax a grease remover. And do it again. Notice in the picture a very small distortion in the carbon fabric.... I chased some spider cracks and sanded just a bit too deep... Oops. It's only the size of a half dollars and I really don't give a fudge about it. Like I said the hood cost pennies in the dollar and some elbow grease. If this was a customers Mclaren P1 hood... Maybe I would have been more careful... But it isn't wasn't and doesn't matter.




Let sit for 5 minutes and begin with the gloss top coat.

Mix the resin. A hood takes generally 8 ounces of resin. Mix it up. Pour about an ounce on the surface and start spreading it with a squeegee onto the hood. This will work the resin into the exposed carbon and saturate the small fibers that were sanded into. Spread it thin and get rid of the excess resin streaks. It is normal for the resin to turn milky in the streaks. Just squeegee it off until its nice and uniform.....




Now it is time to brush on a thick layer. Take a rough horse hair bristle brush and pull the loose hairs off so they don't end up on your hood. I prefer rough horse hair china brushes because the work fast and they are cheap. Foam brushes are **** and fine painters brushes tend to make the resin milky. Brush it on medium thick working in a 12"x12" square area. Then go back over it with light long strokes helping to level out the coating. High solids expoxy is self leveling and smooths out nicely on its own. Don't trip about the brush strokes on the surface.











Let cure. I am done with the how to at this point because the rest is normal clear coat application from a painting perspective. You only really need to wet sand and block to 800-1000 grit if you plan to clear coat or paint it.

This job took 2.5 hours of sanding and 30 minutes of resin application. The resin takes 12 hours to harden and 5 days to cure fully... But. It can be handled the next day.

B and B

iTrader: (3)

Thanks for taking the time to write that up and include all the pics.
Sweet info. Hope you didn't ruin our chances to pick up peeling cf parts on the cheap!
Btw..those brushes are made from hog hair. The ones we get just happen to be made in China, but even American or European made are referred to as China Bristle, for some reason relating to the hog breed or something, which I DON'T know.
I'll be paranoid about getting the loose ones out...seems like like they always shed when I use them for other things. Guess you can pick it off as long as u see it before it drys.
So... most any automotive clear will bind with that epoxy without reactions?
Thank again, brother.

Dallasb84

Yep. "Thanes" go on just fine. Epoxy usually has a amine residue that reacts with just about everything. It's best to wet sand and clean the surface until the water has a continuous surface over ther part. If it beads and shrinks it's still dirty.