[GiorgioE82]

I. Problem Summary

Let’s face it…the carbon roofs look cool AF. But if you’re like me and live in a hotter climate, plus your car spends a lot of time outdoors, you have run into this problem. Mainly, the carbon roof starts to look yellow in areas, then looks flat, then you can see the carbon weave through the top coat, and then inevitably blisters and bubbles begin to appear. These “bubbles”, when torn, reveal the underlying carbon fiber. Also, there are instances where rock chips accelerate the bursting of these bubbles or they outright tear through the top coat.
So, what is happening? In essence, the resin in the carbon fiber is breaking down and degrading due to UV exposure (I’ve also heard some people have had issues with harsh chemicals). I’m not completely sure, but BMW either uses a very poor and thin clearcoat on top of the carbon or does not use anything at all. Again, I do not know for certain which of those is true. But what I do know is what it looks like: flaky, powdery old resin messing up the look of the roof.
In some bad cases, like mine, the issue is so bad that you can actually start to peel off the top layer of resin/clear with a razor blade and the rest will peel by hand. In other cases, if you start when there is enough resin, you may need to sand off most of it for prep.

II. Materials used
a. Two-part epoxy resin. This can be found online or in most automotive paint shops. My wife does hand crafting with resin and she buys hers from an arts and crafts shop. I decided against using this type as I wanted something more “industrial”, for lack of a better term. There are many brands out there and each comes with two liquids: the resin and a hardener. Each manufacturer will specify their mix ratio (either 1:1, 2:1, even 4:1). ONLY follow the instructions specific for your product!!! Kits come in multiple sizes; I’d recommend getting the one that comes in quarts. I had to do with the gallon kit since that is what was available for my specific brand here. For the record, I used the ULV300 epoxy resin kit from Fiberglass Coatings Inc. It comes as a gallon of resin and half gallon of hardener. (see pic).
b. Clear Coat. I went for a 2K Clear version mixed in the can by one of our local auto body stores. It is packed in a can similar to Sp*****x but filled with their product (a clear better suited for our climate here). If you have access to an HVLP gun or paint booth, even better. I used 3 cans of clear.
c. Miscellaneous clear plastic mixing cups. These are to mix the epoxy and resin. They’re cheap and can be found at most hardware, paint stores.
d. Silicone mixing paddles. For mixing the epoxy. Buy a multi pack. You’ll need it. They’re cheap.
e. Sandpaper, or sanding discs. In the following grits (120,220, 400, 600, 800, 1000, 2000, 3000).
f. Nitrile gloves. Things get messy, don’t skip these.
g. Respirator. For use when mixing and putting down epoxy, sanding and when applying the clear. I bought a 3M one for about 30 bucks off of Home Depot and it worked amazingly well.(see pic)
h. Safety glasses. Cheap insurance for your eyes against errant sanding dust, epoxy, old resin shavings and clearcoat fumes.
i. Single edge Razor blades. For peeling off the old resin.
j. Auto trim removal tool. For removing the antenna, and the roof side rails.
k. Acetone. You’ll need to wipe off residue with it.
l. Microfiber towels. Go to Costco and get their 36 pack.
m. Paint brushes. For applying the resin.
n. Masking tape and plastic sheeting. For masking off the area and protect the car from overspray.
o. Machine polisher and accessories. Yes, hand polishing may also work but having a polisher (in my case a DA polisher) helped to speed up the process quite a bit. Don’t forget cutting compound and polish (with their respective pads).
p. Pump Sprayer or Spray bottle. You’ll be constantly spraying water during the sanding stages.
q. Roof rail replacement clips. You know BMW plastics are brittle and (just like I did), you may end up breaking a few of them. Note: BMW has a ton of different plastic clips. The correct part number is:51138045321. They come in a strip of seven pieces and have adhesive backing. About $25 for the strip of 7.
r. Double sided 3M red tape. The same stuff used for spoilers and such. To reattach the antenna to the roof after all is said and done.
s. 1:1 isopropyl alcohol/water mix or automotive paint prep. To clean up between stages in the final wet sanding, compounding and polishing phase. Fireball Reborn, Gyeon Prep, CarPro Eraser will all work.
t. Resintint (optional). To add tint to the epoxy. I’ll explain why in the description of the steps.
u. Air compressor. To help in blowing stuff out of the way, and dry out the roof between sanding stages.


III. Timeframe

The whole thing took me about 4-5 days. BUT bear in mind, that a lot of that time was waiting between curing stages of either the resin or the clearcoat. ACTUAL work time was along these lines:
- Peeling old resin, removing roof side rails , antenna: 3 hours
-Wipe down and masking:1 hour
-Initial sanding: 1-2 hours.
-Actual epoxy application 1-2 hours (with 4-5 hours in between for cure between layers)
- Epoxy Sanding: 2 hours
-Clear coat application: 2.5- 3 hrs ( 4-5 layers of clear with 20-30 mins in between each layer)
-Final sanding and refining, unmasking, antenna and roof rail install: 4 hours.