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Gel Coat Crazing Caused by Air Pockets: Repair Technique

Posted: Sun Sep 12, 2021 8:03 pm
by dyoung16611
I’ve read here and elsewhere that the typical cause for gel coat crazing is related to stress, flexing, and the expansion and contraction related to temperature changes.

I’m offering another reason: air pockets in the fiberglass layup in the original molding of the hulls. I don’t recall anyone citing air pockets in the joint between gel coat and underlying lamination's as a reason for gel coat crazing. Am I the only one lucky enough to have this defect?

On my 1983 15 Striper the hull gelcoat wasn’t chipping off, but it did have significant crazing throughout.

Fig. 1.
IMG_0623.jpg (41.8 KiB) Viewed 936 times

Fig. 2.
IMG_0624.jpg (54.02 KiB) Viewed 936 times

Fig. 3.
IMG_0625.jpg (54.56 KiB) Viewed 936 times

In literally every place I found a gel coat crack, I removed the gel coat completely down to the laminate below, and I found a pinhole void where I assume was an air pocket. To avoid having these cracks print through my new paint job, I removed every one with a belt sander or an angle grinder with a conical shaped 80-grit sanding wheel. In many places, there were so many cracks, I just removed entire sections of gel coat.

If others have discovered air pockets, I’d love to hear how you have repaired air pockets in the course of an AWLGRIP paint job.

ASIDE: my plan for painting after sanding out the air pockets:
  • two to three coats AWLGRIP HULLGARD Hullgard
  • two rounds of AWLFAIR, with sanding and shaping
  • two to three coats High Build
  • three coats AWLQUICK
  • two to three coats TOP COAT
  • lots of sanding in-between

Re: Gel Coat Crazing Caused by Air Pockets: Repair Technique

Posted: Mon Sep 13, 2021 8:08 am
by jimh
Based on your illustration at Figure 3, I would describe the defect as the laminate layer below the gel coat layer was poorly infused with resin.

The hull was molded in 1983, and that is 38-years ago. I do not have any basis to comment on how prevalent air pockets or poor resin infusion occurred in 15-foot hulls molded in 1983.

Regarding where cracks might occur in the gel coat layer due to air pockets: I have a Boston Whaler boat molded in 1990. I have found that an air pocket under the gel coat layer where there is no bond between the gel coat layer and the next layer of the laminate will tend to produce a crack in the gel coat if there is any impact or stress on that area of gel coat. However, I would not describe these cracks as crazing nor would I say there are prevalent throughout the hull.

I have only found two small cracks in the gel coat. One was in an area that was typically covered by another component so it was not visible. The crack erupted when threading a screw fastener. The second was in a section of the deck where an impact to the deck probably created the crack.

Re: Gel Coat Crazing Caused by Air Pockets: Repair Technique

Posted: Mon Sep 13, 2021 8:34 pm
by Jloutrage
The problem you’re experiencing is not due to air pockets, but likely due to the laminate under the gel coat not being wetted-out properly during molding.

Re: Gel Coat Crazing Caused by Air Pockets: Repair Technique

Posted: Wed Sep 15, 2021 6:57 am
by dyoung16611
Thanks Jim and Jl.