Gel Coat Cracking

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makingplansfor

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I have a number of fairly long very thin cracks along the side of the coach roof. This started as a single very small thin crack about a year ago and alarmingly seems to be growing and multiplying. I guess my question is - would 25 year old gel coat shrink or could it be some other cause e.g. in the fibre glass below. There doesn't appear to be any problems I can see under the headlining and the position shouldnt be susceptible to any particular stresses. Also if anyone has any good ideas about first aid to stop the cracks creeping further I would love to hear from them. As always - thanks in anticipation...
 
Cracks in gell-coat are stress related and not uncommon alongside cabin tops. Cabin structure stress can be from winches, clutches and mast movement/bending.

To repair the crack it must be widened to clean it out completely and then new gell-coat applied or you could use flow-coat, it's th same as jell-coat but has wax added so does not need to be covered to effect a cure.

Good luck and fair winds.:)
 
We also have/had stress cracks and I regularly fill them with gelcoat filler. Don't forget when using flow coat that you have to add a very small amount of hardner to it and mix well.

All GRP boats will in time get stress cracks-don't fret.

Peter
 
Stress cracks in gel coat can be caused by many reasons. As gel coat ages it does get more brittle due to UV. the thicker the gel coat the more risk of cracking at the slightest flexing. Usually on corners of mouldings where the gel coat has been applied at its thickest.
Gel coat filler will sometimes work but not if the flexing is still present as the gel coat filler then cracks.

If the cracks keep returning through gel coat filler in the same place because of flexing then a different repair has to be done.
If cracks return due to flexing ensure that any underlying reinforcement such as plywood encapsulations for instance are sound. If everything is sound & it is just a question of normal flexing that gel coat filler cannot withstand without constantly cracking in the same place then the usual better method is to sand/grind the gel coat way in the area for a good distance either side of the crack & overlaminate with very thin epoxy based resin/glass cloth laminate. Resurface with chosen finish & the cracks will not return as the thin lamination prevents the crack showing through again.
A necessarily short explanation but it does work.

John Lilley
 
My quite old boat has patches of this crazing; in this case it might just be age The pros at the local yard said to grind out with a Dremel to clean up the groove then fill with epoxy filler, which is OK for me as it's a paint finish so no colour-matching needed. I haven't bothered yet.
 
I was also told to use a drill bit (by hand) to 'round off' or blunt the ends of the cracks before repairing as this helps prevent them extending further. Not sure this would help if there is underlying damage, but if it is just the gel-coat, makes sense I think.
 
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