Is Gel Coat Prone to Spider-Webbing?

[Patricia Brown]

Hello,

In discussing the pros and cons of gel coat on a different forum, one person stated that gel coat is very brittle and will spider-web crack. This is the first time I've heard this, but it is concerning me, as I just purchased 4 panels from The Corvette Image that come with gel coat already applied!

In your experience, do you guys agree with this comment?

Patricia

[Dave Suesz]

To the best of my limited knowledge...

Corvette panels were manufactured with gelcoat on them starting in 1953, and continuing through production. Gel coat is the outer seal layer on fiberglass panels which prevents wicking, roughness, and generally bad appearance. Boats are manufactured with gel coat as the final finish, this is the color layer you see. Applying gel coat after assembly generally creates a LOT of hand labor, which appears in restorations as a labor charge. And yes, old Corvettes get spiderweb cracks from years of flexing, but it makes no difference when the coat was applied.

[John H.]

Re: To the best of my limited knowledge...

Only '53 and '54 Corvettes had gelcoat on the panels; as each panel was converted from hand-laid to press-molded, the gelcoat disappeared. The original press-molded panels were polyester resin all the way through, and the outer surface simply reflected the smoothness of the polished female half of the mold.

[Christopher R.]

Re: Is Gel Coat Prone to Spider-Webbing?

On boats it is. Spider cracks are very common on boats, new and old, at stress points and small radius curves, either inward or outward. Small radius curves are stress points.

Spider cracks are not common on Corvette panels. They're more common in the paint. But not as much as boats.

[Dave Suesz]

Well, that clears that up...

My experience stripping Corvettes is limited to my own car. What keeps fibers from wicking the paint in press-moulded panels?

BTW, I have seen plenty of spiderweb cracks on C2's and C3's.

[Roy B.]

Re: Well, that clears that up...rocks *NM*

[Patricia Brown]

Re: Well, that clears that up...rocks

So will I necessarily see more spider webbing on a car with panels that are gel coated compared to a car with non-gel coated panels? If boats have problems, and they're gel coated, should I expect to see some cracking?

Patricia

[Bill W.]

Re: Is Gel Coat Prone to Spider-Webbing?

yes gel coat can crack. it has no fibers to give it strength. it also does not flex well.

[Roy B.]

Re: Well, that clears that up...rocks

"spider webbing "Or I think you may mean star cracking, is usually caused by a in-pact of some sort. They are usually found on top of fenders from rocks hitting from under. I've told owners to add-glue a sheet of rubber on before undercoating the fenders (front). I did many years ago when I resorted my 55 and never had one yet.

[Ralph Harlan]

Re: Is Gel Coat Prone to Spider-Webbing?

In my experience there are many variables that affect whether gelcoat will spider crack or craze over time.

Anywhere a gelcoated panel flexes to any degree there is likely to be cracking in parallel lines concentric to the area of the flexing deviation. The larger the expanse of laminate and the less the deviation, the less extensive the cracking. The reason that gelcoat cracks in the tight radius usually allowed for a plane change with boats is that boats (particularly sailboats) flex in use and if the joint between the floor and the sides of the cockpit - for example - is not a large radius, then the flexing is concentrated in a narrow area which then causes it to crack. If there is a reinforcement bonded to a fairly large expanse of fiberglass, then you are likely to see cracking around the reinforcement rather than the large surrounding area of 'glass because the reinforcement will not allow flexing to the degree that the non-reinforced area surrounding it will. It is interesting to note that usually where gelcoat has cracked because of flexing, the underlying laminate has also cracked. I tend to the belief the flexing caused both the laminate and the gelcoat to crack rather than believe the cracks in the gelcoat ultimately transmit to the underlying laminate.

Cracking will also occur to an area that has been flexed due to impact. Frequently, you will find hairline cracks in concentric rings around an area of impact. And many times those cracks do not completely show up for WEEKS after the impact.

The thicker the gelcoat is applied, the more likely it is to crack. If there is moisture entrained in the gelcoat because it was improperly prepped, the humidity was high at the time of application, or moisture was carried over from the compressor during spraying, gelcoat will craze in a random pattern (sometimes very soon after being applied). Moisture contamination of the catalyst can also cause crazing.

One can achieve very good results with gelcoat as a primer/barrier coat under modern paints/coatings, particularly the ureathanes and catalyzed enamels. I have sprayed gelcoat on many, many boats both as part of a repair, and as a base for refinishing with IMRON, and have had few problems in over 24 years. I have also repaired a few fiberglass cars along the way - both with and without gelcoat.

As with so many other things in refinishing - whether the surface is fiberglass, aluminum, steel, or even wood - the experience of the operator with the product in use will determine not only the resulting finish but also the durability of that finish.

[Rich P.]

Re: Is Gel Coat Prone to Spider-Webbing?

Cracks in old original glass panels are caused by something called a resin rich area. What happend is that when the General was making these panels the fiber to resin ratio was not always within specs. The fibers are what give the panel it's strength but only when mixed in the right ratio with the resin. The resin by it's self is very brittle. So most of the resin rich areas (like peaks and bends such as hood openings) will be peppered with little hair line cracks. More so on C1's but still on C2's + 3's.
Now gel coat is pure resin so if it is sprayed on to thick I would belive that it would tend to crack. (But that goeas for any material being applied to a corvette)
I have been restoring and painting Corvettes for over 23 years and personally have never used gel coat, but I have friends that do the same and swear by it.
What does your painter think???

[Patricia Brown]

Re: Is Gel Coat Prone to Spider-Webbing?

Ok. So it sounds like gel coat vs. no gel coat is a toss-up. Without it I could have moisture problems that blister the paint. With it I could have spider webbing issues. So which is the more likely problem?

My new panels from Corvette Image are gel coated already; does that indicate I should gel coat the rest of the car to match? Would I have issues if I left the original panels un-gel coated and the new ones gel coated?

Thanks,
Patricia