Good finish using gell coat?

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jpa_wfsc
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Good finish using gell coat?

Post by jpa_wfsc » Sat Mar 21, 2009 5:36 pm

As I have been sanding off the thick grey mess of a paint job done to my IC by a previous owner or two, there have of course been a few accidents and thus damaged gell coat. Oh no I thought but never mind I am told.

Apparently you can by 25 L of Gell coat for £15 and re-surface the boat - better than paint also! However this told me by someone who repairs newish boats for a living, and I thought I would ask if anyone here has done this to an old (1960's) GRP hull? If so what was the technique that worked best (spray, brush, roll, ??)

Thanks;

j./
j./

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Re: Good finish using gell coat?

Post by JimC » Sat Mar 21, 2009 8:15 pm

jpa_wfsc wrote:25 L of Gell coat for £15 and re-surface the boat
I'm never very convinced by gel coat as a repair technique, but that could just be almost complete unfamiliarity with the material. I've only ever owned one boat finished in gel coat, and cosmetics was not on my agenda with that one! The biq question is whether the boat was built with epoxy or polyester resin. If she's epoxy then the long term adhesion of gel coat is very suspect, and you'll get patches coming away, and you find that the next bit chips away and so on. I'm told the best but very time consuming fix for this is to get all the gel coat off and fill, fair and paint. If she's polyester then AIUI this doesn't apply. Bunging a hole new layer of gel coat on top of the old feels like an awfully heavy option to me though.

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Ed
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Re: Good finish using gell coat?

Post by Ed » Sat Mar 21, 2009 8:26 pm

I don't think Gel-coat will do it....at least easily and without adding too much weight.

Sand it as smooth as you can, put on blakes uni-filler on obvious holes and indents, sand and smooth again.

Put on a coat of two-pack Blakes (or other) epoxy hi-build primer.

Use more uni-filler over holes....more sanding and then another coat.

If the hull was white to start with, and you take care you should only need two or maybe three coats.

two-pack blakes can then easily be polished back to give a pretty glossy finish and its hard and easily repairable.

cheers

eib
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Re: Good finish using gell coat?

Post by Rupert » Sat Mar 21, 2009 10:47 pm

Gelcoat is applied so that the smooth face of the mould gives it it's smooth surface. The layer on the inside not only never looses it's brush marks, but due to exposure to the air, never goes off properly. In a mould this doesn't matter as the glass is applied while the gelcoat is still green, or soft. You can add MW solution (a wax) to exclude air, but you still will be left with a terrible finish, unless you happen to have a handy spray booth and years of practice. Paint is a much better, self levelling, lighter option, whether it be 2 pack expensive stuff or International front door paint. And it will stick to old gelcoat at least as well as gelcoat will, if not considerably better.
Rupert

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Re: Good finish using gell coat?

Post by clibb » Sun Mar 22, 2009 12:04 pm

I agree. Last year we gave up on trying to make our training GP's look good, and we painted them with Blakes, two coats of one-pot. This was on top of tatty gel coat, well sanded to give a good key. I have to say the result has been excellent, the paint sticking well, and looking remarkably good after a season's hard use.

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Re: Good finish using gell coat?

Post by jon711 » Sun Mar 22, 2009 2:43 pm

Having tried to do this on a large area (When I worked at A D Trumans - fixing a Shetland Motor Boat that was damaged in the great storm (1987 - I think)) I would suggest that you fill and paint. Gel coat - even flow coat is a nightmare to get right - it's possible but will take much sucking of teeth and many goes to get it right. If you do go the Gelcoat route do not expect to get the boat afloat this year(or maybe even the next!!)

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Re: Good finish using gell coat?

Post by fatboyfinn » Sun Mar 22, 2009 5:29 pm

Epoxy and bog to fill any imperfections - then more fill, sand with a long board, perspire, repeat - untill desired finish is got. Finally finish with 2 part Polyurethane. And any ikkies, runs and the like can be finished with
1200 grit wet and dry followed by T cut - lovely. Polyurethane is so much harded than polyester.

Andy

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Re: Good finish using gell coat?

Post by STEVEB » Sun Mar 22, 2009 7:29 pm

Hi,
my method is fill with gell coat filler, smooth off then sand the whole boat before painting with two pack epoxy
Steve :o
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DavidC
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Re: Good finish using gell coat?

Post by DavidC » Sun Mar 22, 2009 9:46 pm

It is possible to re-gel large areas successfully and it is done on a regular basis, but it is a technique definitely left for the skilled professionals with the right equipment. The fill, fair and paint is the best option.

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Re: Good finish using gell coat?

Post by jpa_wfsc » Mon Mar 23, 2009 8:26 am

Thanks for all the advice: the balance is overwhelming in favour of two pack topcoat on gel coat repair where needed and filler coats...

Ta!

j./

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Re: Good finish using gell coat?

Post by LASERTOURIST » Mon Mar 23, 2009 8:57 pm

There are different qualities of gelcoat (some for moulding , some for mould coating, some for repairs) and it is a specialist job to do something really clean.
One we did a spray job on some oldish Hobie 16 hulls after some fibreglass repairs.

The thinning stuff to dilute the gelcoat was a 50/50% mixture of acetone and styrène but even with a good quality spray gun the result was somewhat decepive, with a somewhat granulous and dull aspect.

Much better results (shiny aspect) are obtained with a 2 can polyurhane lacquer (Car paints , like Max Meyer paints are cheaper and just as strong as "marine" paints like International Perfection 709)

If you decide to spray new paint or gelcoat DONT CHANGE THE COLOR !....at the first scratch in the paint the gelcoat underneath wll show, much more so if you sprayed with a very different colors.

If in doubt ask a car painter, it is an advice by Ted Welles of US Snipe fame...and it is still valid: I was once given a (tarnished) orange Parker 505 that had been abandoned somewhere in Corsica , almost complete (the rudder had gone in a bonfire...) and I reglued the deck, did some shipwright job on the top of the board, sanded the hull and took it to tke car painter next door who skillfully found the exact shade of orange and made a beautiful paint job...

The boat sold quite well to a guy from Luxemburg and my sailing school bought a more useable Hobie cat, almost new, with the money...

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Re: Good finish using gell coat?

Post by Brian E. Evans » Wed Apr 08, 2009 11:06 pm

As someone who made a living refinishing fibreglass sailplanes that had to be done in gel-coat, I would recommend a good 2 part polyurethane unless you are a masochist.
To do a good job with gel-coat most of the old finish has to come off until you can see the underlying glass-fibre.
The new coat is only going to have a mechanical bond to the old so no finer than 60 grit for the stripping.
If you use straight gel coat you will need a pressure or gravity fed spray-gun, and thin the material the least amount possible to make it spray. If you thin with styrene monomer it will make the material brittle, so the less the better, and if you use acetone it can produce porosity and a softer coating. Also to use Acetone you have to have a warm dry day, or a heated workshop, or the fast evaporating solvent will cause condensation on the surface of your boat.Straight gel-coat will go on like you are spraying porridge.
The so called flow coatings are polyester enamels, and most are formulated without styrene, they do have quite a bit of thinner and cure by drying and catalytic action. They do flow out better than gel-coat.
The bottom line is that in order to get a good finish you are going to have to sand the applied finish starting with 120 grit and going up through the grades to at least 600 grit or better
And as a previous poster said do not change the colour. Another thing,where are you getting 25 litres of gel-coat for 15 pounds? I am paying more than that wholesale for one litre.
Brian Evans.

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Re: Good finish using gell coat?

Post by jpa_wfsc » Thu Apr 09, 2009 6:58 am

Brian, thanks for the advice against - I'm going to go two pot paint. Which brand I've yet to decide.. cost will be significant.

Gel coat - CFS I was told, but best deal I can see there is 20Kg for anbout £60 which is quite good but not £15!!!!
j./

National 12 "Spider" 2523
Finn K468 'Captain Scarlet'

British Moth, 630, early 60's 'Pisces'

!!!! Not CVRDA !!!!
Comet Trio - something always ready to sail.

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Re: Good finish using gell coat?

Post by Ed » Thu Apr 09, 2009 7:31 am

Best value twin-pack is Jotun available on e-bay from guys in london/cirencester.

I have 5 litres in workshop, bought for £35ish

havn't tried it yet, so can't report back.

cheers

eib
Ed Bremner
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