when MUST gelcoat be painted

[Laurance]

Is it correct that old faded gelcoat can reach such a point of degradation that even though it will sand and polish up well, the oxidation will be so deep it will bleed through the surface again within 6 months. The boat is in the tropics and has been sitting in a hot boatyard for three years.

Thanks for any input.

 

[Blueknarr]

Some try to revive an oxidized surface with wax. Wax over oxidation is short lived.
If if polishes to semi-gloss without wax, then it is good to go. Now wax will lengthen the life of the un-oxidized gelcoat.
Eventually, some fiberglass will appear after trying to polish. Then it's time to paint.

Do not paint over waxed gelcoat.

 

[Laurance]

Some try to revive an oxidized surface with wax. Wax over oxidation is short lived.
If if polishes to semi-gloss without wax, then it is good to go. Now wax will lengthen the life of the un-oxidized gelcoat.
Eventually, some fiberglass will appear after trying to polish. Then it's time to paint.

Do not paint over waxed gelcoat.

So as long as the gelcoat is successfully revived by the usual steps of sanding, compounding, polishing and waxing, there is no possibility for the oxidation to reappear provided the gelcoat is kept clean and waxed through its service life?

 

[Blueknarr]

Basically
But
All of the oxidation needs to be removed by sanding.
Oxidation remaining while compounding will shorten time before republish.

Remember
Each oxidation - polish cycle removes gelcoat. Eventually it runs out.

 

[Laurance]

is it obvious when sanding oxidised gelcoat that the oxidation has been removed, since a dull sanded gelcoat might look like an oxidised one too?

 

[ondarvr]

There are too many variables to say how any gel coated surface will age and how well it can be restored.

Not all gel coats are created equal, then the application specifics come into play. A lesser quality gel coat can age far better than superb gel coat applied poorly.

The restoration techniques come into play too. Waxes and oils in the compounds can hide some of the oxidation, which means it may not have been removed thoroughly. When the waxes or oils start to evaporate the oxidation and/or scratches start to be noticed again. So removing all of the oxidation and scratches is important.

Some gel coats don't easily buff back to high gloss even when new, so decades later it's even harder to make it look good.

 

[Blueknarr]

is it obvious when sanding oxidised gelcoat that the oxidation has been removed, since a dull sanded gelcoat might look like an oxidised one too?

And that is the million dollar trick.

Often the bottom of pits contain off color dirt residue. If so, wet sand until they are gone.

As Ondarvr said compounds can mask oxidation.

Don't worry if it falls short the first time. If it needs redoing too soon. Just spend more time wet sanding. No additional damage is done to the gelcoat. Just a but of elbow grease waisted. Or an education gained. Pick your point of view.

 

[wet feet]

I will just add that you can spray a new gelcoat over a properly prepared surface,which means paint isn't the only option.There are a couple of downsides;the overspray can make everything within range sticky and you may well have to wet sand the surface before compounding.On the other hand,you will have a boat that doesn't have the mild stigma of being a painted glass boat.A plastic tent helps with the first of those and a little practice helps with the quality of the sprayed surface.

 

[Laurance]

All excellent advice above, much appreciated.

The boat is an early 2000's Robertson and Caine Leopard 47 cat, reputedly a well built class. So I 'am surprised a professional boat painter in the yard has declared the gelcoat done when i am not aware he has done a test patch of compounding/polishing. A cynic might argue there is bias in his conclusion.

So I am faced with sanding and compounding the entire boat in a stinking hot tropical boatyard. Joy. I have done a good deal of paint polishing but much less on gelcoat, is there a sensible limit on the coarsest grit abrasive i can start the process with assuming i follow the rule of sanding out the scratches of the previous grit when working through the grades? I have seen compounding products from 3m and like that claim they remove sanding scratches from grits as course as 800 but is this wise on a large area? is is not better in general to go to p2000 or higher before getting out the polisher?

Wet Feet, the phrase mild stigma made me smile. Indeed if paint was as good as polyester gelcoat on a GRP moulded boat, would it not have been painted in the beginning. Having dealt with polyurethane painted steel and alu boats for a couple of decades and seen the money that goes into upkeep and the 6/7 year repainting cycles needed to keep the them looking good, i have no doubt i rather live with gelcoat i can keep protected with regular waxing.

 

[wet feet]

You might get the most reliable answer to your question regarding the best grit by taking some 2000 grit to a small part of the hull-maybe an out of the way area to be safe.See how it goes.I would be inclined to try something nearer 1500 and then you can take some compound to it.If it works,you have your answer.It is definitely best to go too fine rather than too coarse as the scratches from coarse abrasive can take a huge amount of work to lose.I think you have identified the root of the suggestion from your painter-if your only tool is a loaded spraygun,every problem looks like a paint candidate.Ka-ching!

 

[Laurance]

You might get the most reliable answer to your question regarding the best grit by taking some 2000 grit to a small part of the hull-maybe an out of the way area to be safe.See how it goes.I would be inclined to try something nearer 1500 and then you can take some compound to it.If it works,you have your answer.It is definitely best to go too fine rather than too coarse as the scratches from coarse abrasive can take a huge amount of work to lose.I think you have identified the root of the suggestion from your painter-if your only tool is a loaded spraygun,every problem looks like a paint candidate.Ka-ching!

a cynic round every corner

 

[fpjeepy05]

All excellent advice above, much appreciated.

The boat is an early 2000's Robertson and Caine Leopard 47 cat, reputedly a well built class. So I 'am surprised a professional boat painter in the yard has declared the gelcoat done when i am not aware he has done a test patch of compounding/polishing. A cynic might argue there is bias in his conclusion.

So I am faced with sanding and compounding the entire boat in a stinking hot tropical boatyard. Joy. I have done a good deal of paint polishing but much less on gelcoat, is there a sensible limit on the coarsest grit abrasive i can start the process with assuming i follow the rule of sanding out the scratches of the previous grit when working through the grades? I have seen compounding products from 3m and like that claim they remove sanding scratches from grits as course as 800 but is this wise on a large area? is is not better in general to go to p2000 or higher before getting out the polisher?

Wet Feet, the phrase mild stigma made me smile. Indeed if paint was as good as polyester gelcoat on a GRP moulded boat, would it not have been painted in the beginning. Having dealt with polyurethane painted steel and alu boats for a couple of decades and seen the money that goes into upkeep and the 6/7 year repainting cycles needed to keep the them looking good, i have no doubt i rather live with gelcoat i can keep protected with regular waxing.

I see the problem much simpler than others, so maybe I'm missing something. Oxidation is on the surface. Wet sand, compound, buff, wax, whatever you want until the hull shines again. If you run out of gelcoat, fiberglass will start showing. That's when the boat needs to be painted with a 2k poly paint or gelcoat with air-drying solution (Duratec, wax, or PVA) personally I think gelcoat and duratec is the cheapest solution, but it will still oxidize, and after a few seasons, you can start breaking through again. Paint is more expensive, but less labor if the sprayer is good. It's almost impossible to spray gelcoat/Duratec without getting some orange peel and that takes some work to remove. Darker colors or warmer climates I'd lean towards paint, in cooler climates and lighter colors gelcoat/duratec might be fine.

 

[redreuben]

The original gelcoat is a more viscous material than that required to spray on a re spray.
Therefore it is a lot more durable, the original spraying gelcoat thinned down to go through a paint gun will cure with a lot more porosity than the original and not be as durable.

 

[fpjeepy05]

The original gelcoat is a more viscous material than that required to spray on a re spray.
Therefore it is a lot more durable, the original spraying gelcoat thinned down to go through a paint gun will cure with a lot more porosity than the original and not be as durable.

Depends on how it is thinned. Duratec clear is 100% solids. No more porosity in the final product. Using a gelcoat gun will also require less thinning. They aren't expensive. $106 for a Sherfab siphon hvlp 1L pot and 3.0mm nozzle.

 

[redreuben]

Depends on how it is thinned. Duratec clear is 100% solids. No more porosity in the final product. Using a gelcoat gun will also require less thinning. They aren't expensive. $106 for a Sherfab siphon hvlp 1L pot and 3.0mm nozzle.

Cool, I’m not familiar with Duratec clear probably new since I was in the game. (Edit) I had a Google, sounds good, what sort of finish will that 3.0mm nozzle give ?
The main factor with gelcoat re sprays is the labour requirement to bring it up to an acceptable finish.
Sounds like Duratec in the right hands could make a huge difference to the quality of a gelcoat re spray, good stuff.