Fiberglass Hood Project
1994 Chrysler Concorde

My buddy bought a 94 Concorde for cheap. It was cheap, because of the mileage and the fact that the hood was all crumpled up. To buy a hood would cost almost as much as what he paid for the car. So since I've been itching to attempt to make a hood, he agreed to pay for the materials and assist me.

We had no expectations of making a great hood. We just wanted to make something that closed, covered the engine, and was strong enough so we wouldn't have to worry about it flying off. So do not compare this to a hood that someone made to look really nice. We are going the CHEAP route on this one.

Luckily, I had a friend with the exact model car we were trying to make a hood for. We called this the "donor hood." This made it very easy for us to make the right size and shape hood.

We are doing a "one-off" and do not need a mould. We are simply making a skin from the top of the donor hood and making a custom frame to stiffen up the hood skin. We are not worrying about latches or making mounts for the hinges to bolt to. We are simply using hood pins in the front and back to hold the hood on.

So here it is. Learn from us or help us with tips.                         Click on the pics for larger views

Step one - Cutting the Fiberglass (FG):

We rolled out the fiberglass cloth and cut the pieces we were going to need. These were set to the side to use later. Always cut your pieces before you start anything else. This will save you from trying to cut pieces while your hands are sticky with resin.

Step two - Application of the Mould Release:

I sprayed the donor hood with PVA. I started with one light coat and followed with two heavy coats. If this wasn't such a flat surface, I would've had runs in the PVA because I was impatient and just wanted to make sure I had enough release on so nothing would stick to the donor hood.

Most people I talk to tell me to put many coats of mould release wax on and then brush the PVA on once the wax dries. They also tell me to wait many hours after the wax to put the PVA on and then wait up to 6 hours for the PVA to dry before laying up your FG. I am sure this is the proper way to do it, but I've never had a problem with sticking and we didn't need a perfect finish on the inside of the hood.

Step three - Lay Up

Once the PVA is fully dried, we started the lay up of the FG. We chose to use four layers of 8-9oz cloth. We put the first layer at a 45 degree angle (I believe it's called "bias") and spread on our resin until it was completely saturated. We then laid the next layer straight across so the weave was at a 45 degree angle from the first layer. We wet that out and continued by putting another layer at a 45 degree angle and the last at the 90 degree angle.

It is my understanding that if you lay the FG at different angles, they will work together to gain strength in all directions.

Step three continued - Wet Out

We applied resin to each layer before placing the next layer on. We made sure all the FG was saturated, but tried to stay away from leaving excessive resin that might add weight without the benefits of strength. (lightweight really wasn't our goal, but we might as well do it right if it doesn't take any extra money or work).

As you can see in this picture of the final layer, we did have a few spots that had more resin than others. Those dark spots really didn't NEED that much and other spots might've needed a little more, but I didn't want to make another batch of resin (cause I'm lazy) and I didn't see it that well until later.

Go a little farther off the edge with the resin than we did. When it comes to trimming, it really helps to have some semi-hard FG to cut. We did this in spots, but not enough.

Step four - Trimming

This pic really shows the little white spots that could've used more resin. If we wanted to do this 'right', we would've finished with a couple coats of gloss resin to give it a smooth/sandable top. Since we are going the super-cheap way, we didn't worry about it.

Once the resin started to stiffen up, we sprayed a heavy coat of PVA on the top to prevent the resin from coming into contact with oxygen.  PE resin will not cure fully unless it is sealed from oxygen contact. This is why gloss resin has wax in it (I'm too cheap for gloss resin, though).

During this stage (aka the green stage), we took a razor and trimmed the edges off. This is the most important part to pay attention to if you want to save yourself a lot of work. If you leave and come back when it is fully cured, you will have a lot of cutting and grinding to do. During the green stage, it cuts like butter.

Step four - Release the Skin

After the piece cured overnight, we popped it off the donor hood with mould release wedges and fitted it to the car. We sanded the edges and are preparing to build the structure ribs to keep the hood stiff.

Step five - Apply the Foam for Structural Ribs

We used triple expanding foam to create structural ribs that we are going to glass over.

It didn't expand like we expected, so we laid more
Step Six - Shaping the Foam

Then we cut, ground, and sanded the foam so the FG would lay nicely over it. We made nice curvy surfaces with no sharp edges or angles. We also sanded the FG so the next lay-up would stick.

Step seven - Glassing the Ribs

Then we used 1.5 oz CSM to glass up the ribs.

Step eight - Mounting our hood pins

I did not do this part. The owner of the car did. He replaced the rubber bumpers with steel plates and bolted it to the frame. Then mounted the pins. Simple as that.

We plan on mounting two more pins on the back, since we decided not to copy the hinge-mount.

Step nine - Pinning the hood

Since the FG is translucent, we were able to see the pins and mark the drilling spots very easily.

DISCLAIMER - I did not mount this hood and would've fitted it better, but the owner chose to just pin it where it laid. So don't blame me for the crappy fitting. lol

I found out this page was being referenced by a lot of people on the web. Since I had no way for you to give me feedback, I didn't realize that. So I'm posting some comments that I found in some forums about this and will give my responses accordingly. If you would like to send me feedback, please use the contact form. Please do not CALL the number. I am not running a fiberglass business and the Customer Service people will get quite mad at me. Filling out the form will send an email directly to me.

Comments:

"You can shape a cowl with cardboard and masking tape and then fiberglass over that. The fiberglass won't stick to the smooth side of the masking tape."

Me: I would suggest aluminum duct tape. My experience has shown that fiberglass will stick to masking tape and regular duct tape.


"Fiberglass is strong for it's weight but brittle, so if it's damaged it will crack into pieces, not bend like steel."

Me: True, but there are ways to make fiberglass flexible.
1) Instead of the cheap Polyester resin, you can use a Vinylester or Epoxy resin. I made a fender that I could fold in half without a single cracking sound with Vinylester.
2) Remove any excess resin. The higher resin-to-fabric ratio you have, the more brittle it will be. Vacuum-bagging helps this.
3) Cure slowly. The faster and hotter you cure the piece, the more brittle it will be. This gets tricky, though. If you don't put enough hardener in or you are too cold, it won't cure fully
4) Use better fiberglass fabric. There are hundreds of different weaves, compositions, weights, and other types of fiberglass fabric. The CSM (chopped strand mat) that you make big boats out of will be heavy and brittle because it takes so much resin to fully wet it out


"Carbon Fiber hoods and Fiberglass hoods are the same thing. When you buy a CF hood, it is just fiberglass."

Me: Not even close. Carbon fiber is a LOT stronger than fiberglass. It is also a lot more expensive. When you buy a carbon fiber hood, ask if it is 100% carbon fiber or if it is just a fiberglass hood with one layer of carbon fiber on top of it. They make 100% carbon fiber hoods.


"You need different resins, and autoclave, and vacuum technologies to make a carbon fiber part "

Me: That is what I thought until I talked to my supplier and they told me I can make a CF part the exact same way I make my FG parts. So I did. Just to try it out, I made a tail for my race bike using 5.5oz 2x2 twill carbon fiber fabric and cheap polyester resin. It turned out awesome, strong, and light-weight. I was the envy of my racing buddies. I even crashed on it and it was easily repaired by slapping a couple pieces of carbon on the inside.


"It was mentioned up there that all they really made was a negative. So is there a different process you need to follow to really do it right, or do you use what they did as a mold to make the actual hood? That seems like it would make sense. You could wrap around the edge of the hood so that you would have accurate edges and all to use, and then you sand up the inside of that real nice to get a good finish on the hood."

Me: If you are making a small part, then it is worth it to make a mold. If you are going to make more than one hood, then it will start making sense to make a mold. But your mold has to be at least 3-times stronger than any piece you are going to make out of it. It also cannot flex or else your part will not be the right shape. So you are talking about A LOT of fiberglass and A LOT of resin -- built around a frame -- to make one mold for a hood. I'd rather spend a couple more hours of sanding one piece than a week making a sturdy mold and then having to find a place to store that mold