Seam Glassing

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Major System Category: Body (Hood/Shell)
Task: Smooth out seams on fiberglass shell
Parts: Bondo, fiberglass
Prerequisite Tasks:
Additional Costs: $30
Time Requirement: 40 -50 hours
Date Started: June  20, 2013
Date Completed:  July 9, 2013

When the body arrives on the truck, it appears to be a single body. Reality is much different. There are five main body parts:

• Hood,
• Rear body shell,
• Left and right doors
• Hatch

Main hood seam. I have the fiber glass cloth just taped in place.

The hood and body shell are delivered as single pieces, but part of the manufacture process involves bonding   different parts together. There is a seam along these joints where the bonding compound has been squeezed and forms an uneven ridge. Also the mated pieces are uneven (i.e. the mated pieces are higher or lower than the other side).

Driver's side seam  that has been sanded down. The fiber glass strip is gut and sitting above the seam.

The hood seams run over the top of the wheel wells, down to the grill and across the front. If your build includes fender louvers, then handle those first. The fender louvers will cover a good chunk of the top seam over the wheel wells. Some people choose to rivet the fender louvers in place, I used 3M's 8115 panel bond to attached the louvers. Then I feathered the ridge created by the louvers to blend into the hood (this is a lot more work).

Passenger side A pillar seam. This looks pretty rough here. I haven't sanded anything, just have the bondo and fiber glass applied.

The seams are uneven ridges along the body. If you are working with a GTM or some other Factory Five model you will notice these ridges. This is part of the body work necessary to complete the car. Most guys that can afford to build a GTM farm this out, but some of us either decide not to or don't have the money to spare. Fiber glassing the seam basically hides and smooths out these areas It isn't that hard to do and after a while you might even get good at it.

Major amount of work. The front hood seam is fully sanded. The entire hood has been sanded once using the orbital sander and secondly using the Dura Block kit. The hood louvers are easy as they are bonded from inside the hood. The fender louvers are a major time investment.

Recommended tools:

1. Orbital sander
2. Dura-Block sanding kit
3. Bondo and fiberglass material.
4. Spreaders.
5. Glazing compound.



I didn't think these were as good as they are. If you plan to work on the body and sanding yourself, then this is a must must buy!

The first thing you need to do is even out the ridge. Some of these ridges are hard and brittle, others can be a little soft. You can use a hand block or a mechanical tool, you just want to be careful about gouging the hood and body shell. Any gouges will need to be repaired. You won't be able to totally eliminate the ridge, because most likely the two pieces that were bonded are an uneven join. Just do the best you can. When you finish no one will see them anyway.

This is the seam that runs the length of the body shell. This is on  the passenger side. This car also has a roof scoop, so you can see some of that work running parallel to the body seam.

Cut a strip of fiber glass cloth for the seam you plan to work on. I would start out short and between 3/4 to 1 inch wide.

This is the passenger side rear quarter panel. The seam runs down and under the car. It is one of those awkward spots to work. It also a little loose, because I have the transaxle bracket currently removed from the frame. This bracket provides much needed bracing to the rear body shell.

Mix up some bondo (this stuff can harden up pretty fast, so get ready). For this I sometimes wore a disposable plastic glove and/or a spreader. I found my finger worked pretty well for some areas where it was awkward to use a spreader. I applied the bondo, evened it out as much as possible then, layered the fiber glass strip over it.

Rear quarter panel on the passenger side. It has bondo and fiberglass applied and still requires sanding in this photo. The body work takes a long long time to do.

I let this set up. Usually, 45 to 60 minutes, then I apply a second layer of bondo over the fiber glass strip.

This is the hardest set of seams to work on. They are curved and in a very enclosed area. This is the big brake vent just behind the drivers side door. I saved this for last.

Once this is hardened up, I go to work with the sanding tools. I use the orbital sander to get rid of the excess, then go to work with a block sander by hand. I work on it until it is fairly smooth. I am using 220 grit, although, I understand you can get away with 180 grit.

To get an idea of the success/failure of my body efforts, I test primed the front seam. For the most part this worked. I still have issues around the fender louvers and the area where the seam goes over the front flare. However, this was a big boost to my efforts, because it showed me that I could get the car to a point where the seams are smooth enough for paint. 

I keep working the seam until I'm satisfied. This gets to be pretty messy.

I ordered 2 kinds of primer for my seam test. I only applied the rapid primer filler. The other one is an epoxy primer that I will test once I am happy with the seams. I got these at 66 Auto color. This is pretty caustic stuff, so you need a rudimentary paint booth or real good ventilation and a respirator.

I wipe down everything using a microfiber cloth and water to remove the main layer of dust. Then I inspect for deep gouges or holes, and use the glazing compound to sculpt in fixes. I keep going over this until I'm satisfied. I keep working it until it is smooth to the finger test.

The fender louvers continue to cause me issues, but I am confident I came make these blend into the car.

The body work can be pretty intimidating, but wow, a little success can be a real confidence builder. I now see nothing that can prevent me from completing this project.