Gelcoat Crazing

[sampaone]

I have a 80's Eagle trawler that was refinished in the 90's prior to my purchase in 2004. It had crazing before the 90's refinish and is crazing again with spider webs and in some places deep pealing cracks. I am going to have it refinished again. Any suggestions on how to prevent recurrent crazing?
Thanks-
SampaOne

[bstreep]

First, you need to find out why you have cracks. Gelcoat does not expand and contract the way fiberglass does, and this is often the cause of cracks that penetrate only the gelcoat. If it is only the gelcoat that is cracking, you'll need to grind out the cracks, and fill them.

If your boat has been painted, 10 years is a LONG time for paint to last - you may just be needing new paint.

[swagman]

With respect to the other opinion, there are millions of GRP yachts out there with no crazing on the gelcoat. In my opinion it is not anything to do with expansion rates - but possibly flexibility.

GRP does flex and is less dense than gelcoat. That is why gelcoat is used for external surfaces - dense means less water absorbtion. But dense also means less flex.

If the GRP substrate is flexing then the more brittle gelcoat will crack. If the gelcoat was applied too thinly then that makes it look even worse.

I agree it could be simply cosmetic - and it can be covered up, but if it is a problem that keep repeating itself then before you fix the cosmetics first stiffen up the area from behind.

All IMHO of course. Good luck

JOHN

[Southern Star]

Sampaone, welcome to the forum! Bstreep and Swagman are correct - gelcoat cracks are the result of flexing in the GRP hull/deck and will recur if the cause is not corrected. If it is the result of inadequate construction, the hull/deck will require reinforcement in the areas in question - a very expensive proposition. If the cracks are the result of collision damage, then so long as the laminate was not also damaged, it may be possible to grind out damaged areas, fair with epoxy and paint or re-gelcoat (and from your description, I am assuming here that the boat was refinished with gelcoat rather than paint).

Crazing can be the result of exposure to the sun, overly thick gelcoat or excessive catalyst - and again, repairs can be made by grinding (or sanding) out the affected areas and repairing with either epoxy, or gelcoat.

Peeling gelcoat suggests improperly made repairs - if epoxy was used to repair a damaged area, then a special technique must be utilized in applying gelcoat over top of the epoxy (and some manufacturers recommend that it not be done at all).

From your description of the extent of the damage, I would recommend repairing the affected areas wtih epoxy and then repainting the entire boat. Once again, you must keep in mind that cracks that were not caused by collision or dropping heavy items on deck, will require reinforcement of the hull/deck itself or the cracks will reappear.

Brad

[roverhi]

As has been stated, the problem is difference in flexibility of Gel Coat and the FRP laminate. Most of the time, the problem is the thickness of the gel coat. If the deck was laid up outside, like in SoCal, on a cool day, the gel coat will flow to the low areas before it goes off. The worker who sprayed on the gel coat often would just keep spraying the gel coat to get full coverage in areas where the gel coat was flowing from. This resulted in way thick gel coat in the areas that the gel coat flowed to. In other instances, it is just poor construction technique with the worker spraying it way too much gel coat. There are also boats that have too sharp bends in the laminate make for cracks. The Tartan 34 front cabin to deck junction is an example. Most of these boats have cracks on the deck in that area.

If the gel coat is too thick, all you can do is grind it down to the FRP underlayment. I had to do this on my W32. Tried widening the cracks with a grinder and filling with thickened epoxy. Practically everytime I went back to the boat, there would be more cracks to fill. Finally just bit the bullet and ground the cabin top and walkways down to glass and that solved the problem. Didn't do much for itchy skin, however.

LPU paints like AwlGrip are more flexible than gel coat and usually won't crack like GelCoat. If you get rid of the gel coat, there won't be a cracking problem later. In many cases, the thick epoxy primer used in LPU paint jobs will cover up small cracks. If the problem is the underlying gel coat continuing to crack, however, the cracks will eventually reappear.

Aloha
Peter O.

[GordMay]

See also ☛ http://www.cruisersforum.com/forums/f55/a-primer-on-fiberglass-construction-619.html

And ☛ http://www.cruisersforum.com/forums/...t-1-a-944.html