Technical Tech Week: Fiberglass Repair or How to Put Humpty Dumpty Back Together

It seems that on some regular basis, there are questions that pop up here on the HAMB about how to repair some fiberglass issue, whether it be a small crack in something or some major repair. As much as we all like steel cars, some of the ones we like, and from the era discussed here, are either made from glass from the factory (like vettes) or might have some aftermarket fiberglass parts like a front clip, etc. on a gasser or otherwise that maybe we won't specifically mention here.

Anyway, the techniques I will discuss here can be used on the early factory fiberglass cars and most aftermarket fiberglass parts up to ones even made today as long as they are made from traditional fiberglass with polyester resin and not something like smc. Anyway, I’m sure there are many other ways to fix this stuff, but I am just going to share what I know and has worked for me. I learned some of this from my Dad that fixed several vettes when I was a kid including a couple mid-year cars that went through fires if you could imagine what that was like. For history, first pic is me standing in front of one of my dad’s vettes that he bought wrecked when I was a kid and another one he fixed that went through a fire. I have been around this stuff for a year or two… I got most of my own experience on this stuff fixing a pretty butchered up 67 vette roadster about 25 years ago as well as modifying a few fiberglass scoops. Then, later I built a complete hood and some fenders for a very OT machine where I work.




So, as my example for this tech thread, I am going to use a one-piece front clip off a possibly familiar SEGA car named Bad Banana that has been a gasser since the mid-60’s and has been documented here as far as the rebuild once Rusty got if from his dad. This 55 Chevy 2-door hardtop was built by the Rusty's dad who put the front end on it in about ’65. So, when it ended up in a wall last year because of a very unfortunate incident, and the front end was in lots of pieces, it started to make sense to fix a fiberglass part that could have likely been replaced for less money and definitely much less time. But sometimes we work hard to save things that some folks don’t think should be…but they don’t get it. Disclaimer...some pics stolen from Rusty's thread on the car.



So, step one would be to try to collect up as many pieces as possible to put Humpty Dumpty back together again. The more pieces you have, the less that have to be formed from scratch. Thankfully, Rusty found about 98% of the front clip, so I only had to fill in a few gaps that we will get to later. After we collected all the parts, I tried to sort of start fitting it together to see where everything went.



Once I got that figured out, I started grinding along the cracks to start putting it back together again. I started with the inside, then moved to the outside once it was all one piece again. On something like this, the goal is obviously to end up with something the same shape as it started, so the order of putting it together has to be somewhat paid attention to. Also, if you don’t hold the thing somewhat the right shape overall, it could be pretty easy to get a twist or something in it to where it didn’t want to sit back at the right shape if not careful. So, since it was pretty floppy at first, I tied the two sides together to hold the overall width and had it supported on some saw horses to keep it as much in the right shape as possible. Once I got all the cracks ground down with 36 grit, I started clamping areas back together with c-clamps and little pieces of stir sticks to prepare it for putting about 3” strips of fiberglass cloth along the cracks to sort of “sew” it back together.



I basically followed this method of adding about 4 layers of 3” strips along the cracks wetting it with fiberglass resin until all the pieces were put back together. In the areas where I clamped it, I had to go back and fill those areas in once the resin dried from the area next to them. Once the resin dries, it has to be roughed up again with something like 36 grit before adding more fiberglass to make sure it adheres as intended. Since I was doing this in the evenings for the most part, I would prepare an area, cut my strips, and then only tie together one area leaving it overnight until in could harden good and I could repeat. This was partly because of time constraints, but also because I only had so many clamps to hold the thing together. I suppose if I would have went out and bought a bunch of clamps and stayed up later every night, the process could have went faster.

Anyway, once it started looking like something again, I had to start filling in the gaps where pieces were missing. If that gap happened to fall in a flat area such as the front valance panel, I could just use something like a 2x4 covered with wax paper to make a “mold”. If it was something like the fender extension under the marker light, I used some foam that is somewhat easily carved to be the right shape and also cover it with wax paper so there is a release for the resin.





To be continued...

 

Once all the gaps were filled in and the inside was pretty solid again, I was able to flip it over and do basically the same process on the outside. I would rather make sure that all the cracks are covered with fiberglass cloth to make sure they don’t try to crack again later. By the way, cloth is what I prefer to use instead of mat since it is much more pliable as well as stronger than mat. From what I understand, the mat is more for building thickness and the cloth is more for strength when thickness isn’t needed. And, since we all know we don’t want to see these “stitches” at least on the outside when done, keeping it as thin as possible is important.



So, once the seams were all “stitched” back together, it was on to basic bodywork like we all know and love to make it look like this never happened. There are plenty of folks that have talked about how to do that, so I won’t bore anyone with the details. However, once I got it back in shape, I primed it with a good filler primer so someone else could finish it up when they had more time. Rusty was trying to get to a race, and my procrastination on getting started in the first place didn’t leave me enough time to do the paint repair. Anyway, hopefully that can help someone that might need to do some glass work. Other than being pretty itchy to work with, I have decided I like working with fiberglass more than metal anymore. Yea, I know I am kind of weird…




As the final pic...I just went and searched Rusty's thread to see that it has now been painted. So, looks about like it did again before the crash.

 

bITCHIN'!

 

Great, itch, work, itch

 

Looks good

 

A nice repair you have made there.

 

Great tech Jeff!

 

Love the OSHA approved footwear! Nice job, enjoyed the tech.

 

Lol! Yea, trying to teach this stuff to my kids and I can’t hardly get them to even wear closed shoes... I’m just thankful that they don’t mind being in the shop.

 

On the plus side, if enough resin drips onto their toes, sticking them together, just think about how fast they could swim!

 

Nice work but I itch from just looking at the photos.

 

Yea, the itching would go away after a couple hot showers. But, when you do it every day, it pretty much stayed until I was done.

 

Great tech Jeff.

 

Hot shower OPENS the pores in your skin allowing material to enter the pore , itches whereas cold water CLOSES the pores , allowing the material to be rinsed off , not as much itch . There's a product called " Barrier Cream" , applied to skin before you start helps considerably !
Zep Barrier Cream

 

Very nice repair. I do much the same but only had to do small jobs. Nice tip on using foam for shape. I guess your son learned that working with fibreglass without long pants, shoes and sock, and longs leaves is a "real son of an itch"!

I would have not primed it and named the car Scarface!

 

Nice repair of a piece of history.
My oldest worked in industrial insulation and did the same routine when working with fiberglass.

 

Here is a tip about itching , try putting Vasaline on your exposed skin before you start.

 

Great tech article and good job on the way you presented the information.

 

Thanks for the tip! I think someone may have told me this before, but apparently it didn’t stick. I will have to try that next time.

 

You didn't mention type of foam. Green florist foam won't dissolve.

 

Well... Once the repair is complete there should be nothing remaining of the crack, it should be completely ground out and ALL the damaged material replaced by new fiberglass and resin. If any of the damaged stuff is left in there it's a weak spot that may break again sooner than you like.

If there's a mold for the damaged fiberglass part available (or a non-damaged part to make a mold off) new partial pieces can be made, this may save time and make a better result than trying to put 20 small pieces back together. One big repair piece to splice in, one joint to get right instead of 20.
Sometimes another option can be cobbling all the broken pieces together to the right shape just to make a mold of, and then make a brand new part in that.

For a racing car that is likely to get fiberglass damage sooner or later I'd want to have the mold for all the fiberglass pieces. If you have the mold, making a new part can be quicker than repairing a damaged one.

 

I followed the bad banana thread and he got me hooked, watched some of his runs on yt. When I opened this thread and saw your Ford in the avatar window with the bb hood, I was massively confused! Lol.

Good thread. Dig it.

 

Good point. I use a blue polyurethane foam that comes in big chunks and is fairly easy to shape. I bought a few boxes with pieces that are like 9" x 20" x 36" or so when I built a fiberglass hood a few years back if I remember right. I tried to do a search just now to specifically figure out what brand it was. I know it is the same that I used when I worked at a place that built aerobatic planes where we used it to build plugs for carbon fiber part molds. If anyone does want to know specifically what I use, I can get the information off one of the boxes in my shop.

 

I completely agree that it would have made more sense to just use a new part for this. A 55 Chevy front clip is likely one of the most common fiberglass front ends and readily available. The only reason we saved this specific one is because it was part of the history of the car. Otherwise, it made no sense to even save it. Also, I agree on getting rid of all the damaged glass so as not to have a weak area. I ground anything that was weak out as I put it back together for that reason. Thanks for the comments.

 

Just realized I never posted a pic of the inside of the hood once finished. Tried to make it appear that it hadn't been repaired as well although also wasn't overly concerned so didn't do any bodywork beyond just the fiberglass repairs. Rusty's dad had sprayed a spatter paint similar to what 60's cars had in the trunk on it a long time ago and since we were trying to retain this car's history, that was perfect to hide these repairs as well. I was unable to find the specific color that he used, but made my own spatter paint from a paint trick I learned back in the 90's when the whole "granite" look was big on custom bikes and mini trucks. Anyway, I suppose that could have been a tech thread in itself on how to make spatter paint from a gun, but I'll just post the finished pic. Thanks again for all the comments guys.

 

Kind of reminds me of the green Zolatone that the Army used to paint half walls in the latrines. Spent a lot of time scrubbing those walls. Still hate that color. But I really like what you did with the underside of the hood. All in all an excellent repair.

 

Thank you very much.

 

When you grind out the back side, do you grind it with a taper...ground down thin at the actual crack, and tapered away from the crack? Also, on the top side, do you grind it down to the new glass repair at the crack and also taper the grinding away from the crack, like on the back?

 

Dad used to build fiberglass front ends for guys , back in the day.

 

That's how i would do it.