How To Get Overlaid: Our Carbon Fiber Overlaying DIY

How To Get Overlaid: Our Carbon Fiber Overlaying DIY

Step 1: Don’t be Tom. But in all seriousness, your blog post today will teach you the ins and outs of a carbon fiber overlay in a few easy (?) steps.

Okay, maybe it’s not just a few steps. And for some, perhaps it’s not entirely easy. However, for the sake of brevity, we will attempt to keep it informative without going overboard on minute details and the like. Let’s start with the item in question. Today, we’ll be doing a carbon-fiber overlay to the top of Eric’s Z4M airbox, which we finished building last week.


You may be asking why the airbox is covered in cake frosting. It may look like frosting, but it will probably kill you upon ingestion, so we don’t suggest you sample the goods, so to speak. Since the goal before overlaying carbon fiber is to make everything as smooth as possible, you may as well attempt to minimize the welds while still retaining the airtight properties of the box. One way to do this is use small, carefully-placed welds on the inside of the box, while using the quick-drying cake frosting to fill in any gaps between metal panels. The cake frosting will dry, and you will have an airtight box that you can then smooth down to the necessary amount without worrying about compromising the structure of the welds. As with all things of a delicate nature, go slowly, and your patience will be rewarded.


Since the carbon fiber we’ll be using can potentially let light leak through (if the weave has even a sliver-sized opening anywhere on it), you’ll want to ensure that the reflection doesn’t show bare aluminum (or whatever else you’re overlaying) underneath. For that reason, a quick hit of spray paint will give the overlay some more depth to it and protect against errant reflections. Once the paint’s applied, sand it down to create a smooth surface once again. If you need to, re-apply paint to hit any areas you might have over-sanded.


Next, you’ll need to start mixing your epoxy resin and your hardening agent. Make sure to use proper amounts of each, or you’ll end up with a mess on your hands that may end up nigh impossible to fix. While you mix it, small little bubbles will appear. How magical, right? We forgot to mention there’s a lot of magic involved in this, too.


Next, you’ll want to lay out your woven sheet of carbon fiber (CF) that you’ll be using for the overlay. Once you do, pour some of the resin onto the bottom side of the sheet. You’ll want to make sure your CF sheet is oriented in the proper direction (if you’ll be matching it to an overlay on another piece), so there’s a bit of spatial preparation involved here. Spread the resin out thin and evenly; it’s a very powerful bonding agent, and will provide more structural rigidity to the piece than the sheet of CF will, so treat it properly. Make sure the surface you’re working on is covered by something you can throw away later, like plastic sheeting. Also, you will want to wear gloves for this.


Once your carbon fiber sheet is properly layered with the resin, you can then lay it onto your piece. You may want to do a dry run before applying anything to the sheet, just to make sure it will lay where you want it, the way you want it. Be careful as you’re applying the sheet to the item in question, as any excess forced applied to the CF sheet will run the risk of separating the weave, which will result in a lot of swearing and misdirected anger. Go slowly. Once you’ve laid the first face, you can begin working the CF sheet over the various contours of the piece. Use a paintbrush (or something similar) and the remaining resin to help the sheet hold itself against the item in question. Resin takes hours upon hours to dry, so there’s room built into this job for taking your time, we can’t stress that enough. Just because we hit this airbox in the first try doesn’t mean that it’s easy, practice is key. You can also use your gloved hands to apply the resin and smooth the CF over the corners, just make sure to apply a light, constant pressure.


After you’ve used the resin and brush to work the carbon fiber over the various smoothed edges of the piece, make sure everything is staying put, and place it under a heat lamp for curing. After 6 to 8 hours, the resin should have cured correctly, provided the whole process leading up to the curing went off without a hitch. An hour or two into the curing process, you can return to the piece and cut off any excess CF that won’t be attaching itself to the box, like we did. Our CF overlay will be draping less than an inch over the corners, but it all depends on what you decide to wrap.


We know some of the pictures are a bit bright in spots; with the lighting in fabrication being how it is, and with the reflective properties of the woven CF and resin, it’s tough to find an angle where light isn’t directly reflecting into the lens. Either way, from here, you can sand the resin down for a smooth, consistent finish that can then be covered in a clearcoat for maximum protection and that glossy look you see on pieces such as Bimmerworld’s CF airbox. We’ll be masking off our overlay and repainting the remainder of the airbox as a final step, but your end steps may vary. We hope you learned a little bit more about what goes on when you’re looking to get carbon fiber overlaid onto another material. Have a great day, and drive safely!

  • Amir
    Posted at 21:30h, 25 January

    cake frosting = bondo? hopefully not actually cake frosting lol

  • Robert
    Posted at 21:51h, 13 January

    There’s an easier way of doing it.

    Don’t apply resin before laying the carbon fiber fabric over the piece. The chances of ruining the weave is too high.

    Resin is not sticky before it starts curing so it is of no use in sticking the cf to the piece. You can apply a layer of resin to the piece first and wait until it has cured a little but is still sticky. Then apply the cf fabric dry and it will stick to the contours. Then apply resin on top and let it soak in.

    A quicker method and one I prefer is to use a spray glue on the piece before applying the dry cf fabric. Then. applying resin on top as before.

    You shouldn’t sand the cf.. You will just scratch the weave and ruin the strength. You can get a smooth finish by either wrapping the cf in something smooth during curing that can be removed later (like a rubber female mold) or putting it in a box for curing and then putting the box in a vacuum, bag before sucking all the air out with a vacuum cleaner.

    If you have lumps and bumps after curing, you will next being able to sand it down to a smooth surface after. You screwed up. Throw it away and start again if that happens.

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