How can I repair my gel coat?

[Ginfizz]

I have a old 1970s GEN fizz sailboat that has some extreme crazing on the gelcoat.
Some spots of the crazing show chips, but around those chips it appears that the gel coat is it adhered well to the fiberglass. I’m thinking about grinding everything off above water line only and putting a new layer of glass, but I don’t know if that’s a good idea.


I have also dabbled at the idea of fairing over the rough patches with some sort of poly fair and then just gel coating over as a temporary fix that would last me for hopefully two years
I think the damage is from a previous repair that was not done well.

I need to get it out of the boatyard asap and I am trying to get a plan together for this weekend. I have 3 gallons of poly resin and 4 gallons of gel coat on hand.

 

[Ginfizz]

 

[greeny]

Sounds like a lot of work for a weekend. Especially given the weather forecast this weekend in the UK. Assuming the boat is in the UK that is. Is the boat in a heated shed?

 

[Keith 66]

That is an excellent example of an old gelcoat that is failing all over, Its what happens eventually. As to what you can do? Sand it all back & put a skim of epoxy & microballoons over it, fair it then paint.
Or Sand it all back & apply several coats of hi build epoxy primer, fair & paint.
Do not even think about doing it in winter time, you will never heat the boat or shed up enough.
Its a summer time job.
If you go ahead & try to do it in winter time when its cold you will simply waste gallons of epoxy & paint.
If you think you can do it with polyester it wont cure either & you will do the job twice over.

 

[William_H]

Gel coat is in fact normal polyester resin with pigment in it. It is the first layer of resin applied into the mold. It is called gel coat because it is allowed to harden toa gel state before the actual fibre glass and resin are applied. The gel state means the glass fibres can not penetrate to the mold (outside) but the gel state not fully hard means the resin (with glass fibres) chemically bonds with gel coat to create when all is hard a smooth shiny outer layer.
Now OP says he has 4 gallons of "gel coat" on hand. Which is unlikely. There is a product called "flow coat" which is fairly thick resin with (usually ) white pigment which is designed to be painted on the inside of a finished hull to smooth out what is other wise rough glass fibres.
At a pinch this stuff might if the correct color fill some of the dings in the hull.
But essentially polyester resin is not a good adhesive even to original grp the same material when GRP is hard (years old) But it does stick to itself if the resin is newly made and not fully cured.
So ideally epoxy resin is afar better adhesive. But also your 2 pack polyurethane paints are excellent adhesive to old structure of any sort.
The proper fix to your hull is to fill and flat the holes with an epoxy filler then paint the whole with 2 pack paint. Just clean the surface before painting no need to grind out the dings and crazing to any great degree.
Now I am a bit of a rough bodger and perhaps foolishly painted my grp boat with polyurethane white using a brush. It is hardly a shiny example but has allowed me over the years to easily patch up more scratches etc and keep it looking good at least from a distance. I also did the deck. Which was a mistake in that the original was beige color and the bright white is very bright in the sun and secondly it filled to smoother the non skid areas. So I had to add more paint and non skid grains.
As mentioned all this painting requires warm weather. The flow coat can at least be mixed with extra hardener to go off quicker in cold weather.
In any case get the boat out of the yard and into the water where you can enjoy it. You can't see the scratches etc from the cockpit. ol'will

 

[Stemar]

Looking at the photos, I reckon that the surface is beyond simple restoration.

My plan would be to spend the winter getting a good surface, polyester resin will go off eventually, even in cold weather, though I'd try to find milder days to do it. Then, when the weather warms up, a coat of primer, which will show you all the bits you missed, fill, sand and prime. Yes, you still missed a few bits, so repeat. And repeat until you've got it all good or, more likely, you've just had enough. No one but you will see the imperfections at this point anyway. Final rub down and a couple of coats of two pack paint. This will need a warm - 10 deg +, dry day. Ideally, you want two people, one to roll the paint on, the other to tip it off using a Jenny brush. Google Roll and tip boat painting for vids and techniques.

I appreciate that this is incompatible with the need to get it out of the boatyard asap, but I don't think there is a quick fix. If you have to leave it until you can plan the job properly, so be it. As ol'will says, you can't see the scratches from the cockpit, and the boat won't suffer any more.

BTW, for sanding, use a random orbital sander, That will avoid the circular scratches. Roll and tip won't give you as good a finish as spraying, but you won't see the difference from more than a couple of metres away, and no one else will notice at all. Actually, if your spraying skills are anything like mine, roll and tip will probably be better.

 

[Refueler]

Looking at the photos - looks like somebody used a sander and created all the swirls ..

Difficult one to advise ... but a sanding to create a bondable surface ... then something like FineFill (International used to have such a 'paint' designed to level / fill sanding damage) ... repeated coats until its built up ... orbital fine sanding between ...

But its a Summer or heated shed job.

 

[vyv_cox]

I watched a couple in Greece completely re-gelcoat topsides on a 38 ft boat. They ground off all the old gelcoat and flatted off using a belt sander. New gelcoat applied by roller in about 4(?) layers, flatting off between as needed. Finally progressively finer sanding followed by polishing. It took about a month, applying one layer per day.

Lots of work but looked superb at finish.

 

[Keith 66]

Gelcoat is formulated to cure with a tacky surface if exposed to air, this is because its used in moulds where the tackiness is required for subsequent laminating.
Flow coat is simply Gelcoat to which a percentage of Wax in Styrene has been added, you can buy the wax solution separately & mix it yourself. The wax migrates to the surface upon cure & inhibits the air allowing a non tack cure.
Using flow coat for subsequent coats requires sanding & degreasing or poor bonds with further coats will result.
Cured gelcoat does not sand or fair easily which is why most boatbuilders use hi build epoxy primer, simply put it saves a world of sanding.
Getting a good finish with gel isnt easy, probably the best way is a gelcoat gun & spray the stuff, however gel guns use a lot of compressed air so you need a big industrial compressor to use one. I had one for a while & my 5hp 3 phase compressor with big 16 cfm V twin pump could barely keep up with it.
From bitter experience if you work in winter time & get a failed cure you have no choice but to scrape the lot off & start again.
To be honest if a boat has a gelcoat like that it probably isnt worth doing. Slap a coat of rubber paint or tar on it & go sailing.

 

[Stemar]

Provided the rest of the boat is in good condition, I reckon it's worth doing, but I'd be looking at coming out of the water as everyone else is going back in, and spending the spring prepping and painting. That way, you should get a cheaper rate for the yard and some decent weather by the time you're ready to paint.

I don't think you'd get into Quay Lane, but Wicor Marine in Portsmouth Harbour may be able to help, and I would expect them to be more reasonable than some of the yards near the harbour entrance. Portsmouth Marine Engineering in Fareham may also be worth a call.