DIY Fiberglass brake ducts

[Lazeum]

I just wanted to share how I did the ducts for my airdam. here’s the how-to.

It is not fully done yet, I need to trim them good & paint them.

 

It was my first experience with fiberglass, I took whatever was available at the hardware store (no more thin fiberglass cloth, only thick coarse mat). It was actually a little bit too thick, it was not so easy to work with; it was too stiff so I had to cut small pieces in order to go around the geometry of the ducts.

 

It is a process that’s quite messy with toxic products so appropriate protections are required: googles, gloves, mask are the minimum. Get some dirty clothes as well, if you ever drop some resin on your brand new pants, it is over.

 

Other lesson learned during the process is to do not use plastic cup to hold the resin. Mine has melt in the process, process became even messier than it already was!

Last advice, pay attention to draft angle or you may end up with extra work to do (like I did L; see the last steps below )

 

 

So first you need some products for fiberglass molding:

- Some FG mat

- Some polymer resin

- Some hardener (often provided with the resin)

- Some unmolding wax made specifically for FG.

- A brush, a glass and a stick to mix resin & hardener together

- Many gloves!

- Acetone to clean the brush and the glass

 

As an option you can also get some clearcoat for a better finish but since the ducts won’t be so visible, I’ve skipped this step to save some $$$$ & time. If I would have found some black clearcoat, I would have ended with some just because it would have avoided the painting process.

Best practice would have required the use of a roller. Since it is not a structural part, I decided to stay with basic tools. The roller is basically a stack of small and bigger washers around a steel rod. I could have made one myself. If I would have to start over again, I would do one, I think.

In addition to get the shape you want, you need:

- Some plaster

- Some spray can cap to give the round shape for the hoses

- Some rubber bands to create a flange at the tip of the ducts

- A sharpie

- Some sandpaper to get the finish you want before molding (optional)

 

To make the shape, I’ve thought & try several options, the best being for me some molding plaster: 4$ for 4kg. Depending on water quantity, you can choose the viscosity which is quite convenient.

The hardening process is slow (30 minutes) so I had some time to get the plaster in shape with a sharpie.

I’ve also used some spray paint caps to get a round shape for the hoses that would clamp on the scoop once done, a tube, big hose or anything round would also have worked but I took what I had. Just make sure hoses you’ll end up using would match the outer diameter.

I’ve tried expandable foam also with no good result.

 

The process now.

 

1. Get the airdam out of the car

 

2. Fill the brake duct holes with a piece of cardboard box cut to the shape of the holes and paint tape to seal them (to avoid plaster to go everywhere). Make sure you leave a small dish to have the plaster being able to locate itself. It will also avoid the plaster to move during the whole process. Pay attention to do not leave negative draft angle or it will be difficult to get the plaster out of the airdam afterwards.

 

3. Pour some plaster over the filled holes, give the shape you want for the duct and put spray can cap on top of it. Get the plaster roughly in shape. (I would recommend using gloves for this operation). This is the step where you need to most to think about draft angle if you’d like to unmold everything easily at the end of the process.

 

4. Let the plaster become a little hard (5 minutes?)

 

5. Start shaping the plaster with a sharpie, it should be still soft and easy to play with. With time it becomes harder (and hotter), you can then get a better finish, plaster starts to become brittle.

 

6. Let everything dry for at least 24h when you believe the shape is the one you want. You can also clean any excess around the duct shape with a wet sponge.

 

7. Since plaster is porous, once it has dried out, we have to cover it with regular wax. I have used a candle, hot enough (I used hot water) to have the wax soft. I have scrubbed the wax all over the plaster. I’ve done it twice to make sure plaster was sealed.

 

8. With a paper towel, I then spreaded all over the shape and all around on the airdam some unmolding wax. I’ve put 3 layers; each needs to dry off & to be polished prior to apply the next one. I put some up to the face below the side light housing since I will locate one of my bolt/rivet to attach the duct below to hide it once finished.

 

9. Now it is time for fiber glass work.

a. Start by getting some small pieces of mat before having your hands full of sticky resin. I did not cut them with scissors to avoid having straight edges we could have seen on finished part.

b. Once resin is mixed with hardener, start by spreading resin all over the piece you expect to build with the brush, be generous.

c. Put 1 piece of fabric on top of the resin. Resin you’ve applied before will help the fabric to stick to the shape you’ve made.

d. Apply resin on top of the fabric to mix it with the first layer of resin, tap with the brush to spread the resin thru the fabric & to remove any air bubble.

e. Continue until you’ve covered the whole area. Go a little bit over it, you’ll trim the excess afterwards anyhow.

f. Once first layer is done, I’ve installed some rubber bands to create the flange.

g. Apply a second layer everywhere for strength, it will also trap the rubber bands in the resin.

h. Let the resin cure for at least 2h

10. Next step is what happens when you did not pay attention to draft angle; I had to cut the piece to extract it over the airdam.

11. Next operation was the trimming of the piece freshly made. I’ve used a Dremel with a cutting disk. It is very easy to process.

 

12. For a good finish, I use the Dremel again but with a sandpaper grinder to smoothen the edges and any irregularities.

 

13. Following step was to fix the cutting operation with some more resin and FG mat to close the shape. Since I wanted a good finish, I’ve put some resin outside but also inside.

 

You now have 2 ducts ready to be installed on the airdam to receive hoses.

 

I will also install a grid to avoid rocks to go inside.

To install the grid, I plan to drill little holes into the fiberglass and use some ties to hold the screen. I was also thinking about making the grid going thru some holes and to use some more resin to hold everything back together.

 

Overall it is a messy process but it is quite easy to do. Cost was also quite ok, I might have spend around 50$ total.

[santanawhite]

Thanks for the 'How To'. I might do this.

[didier]

Good job , Matt, you could have made it with epoxy,lighter, stronger, but costy !

[Lazeum]

Thanks guys. Didier, you know, weight is around 50-100g per part and it is way strong enough. so cheap sometimes is good Since then, I've added a grid. Paint will follow this weekend. I'll put picture of the finish product afterwards.