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Old 21-05-2008, 19:11   #1
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No sag gelcoat??

Well, the boat is on the hard, and last summer we filled about a 1000 gouges on the stern (ex-commercial fishing boat). Now, we are trying to figure out how we can do a half decent job of applying gelcoat to those verical surfaces without it sagging on us (which is our usual experience with Evercoat). Due to the location in the boatyard, we won't be able to use a spray. Does anyone recommend a brand of gelcoat that can be applied by brush on a veritical surface without getting the sag marks? I suppose their are some clever techniques that some of you know as well.
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Old 22-05-2008, 00:25   #2
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You can not use Gelcoat on the outside. Gelcoat will only harden in a Female mold between the mold and glass/resin. In other words, it has to be kept from air.
You are best to fill the gouges with filler, fair and sand and paint with a two pot paint. Paint will allow you to roll it on.
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Old 22-05-2008, 01:26   #3
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Alan - not sure I'm following your assertion. I've had great success applying gelcoat to exterior surfaces (hull) with both spray and brush and it's a routine repair job. What am I missing?
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Old 22-05-2008, 05:40   #4
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Billr, you could try some Duratec additive & tip it out with the brush vertically. Also with the addition of a wax in styrene solution to the gelcoat it is tranformed into flowcoat & the surface cure is no longer air inhibited, a few coats can be applied wet to tack & also tipped vertically with the brush & a build of coat can be acheived & once well cured use wet & dry abrasive & polish to finish. The verticle tipping helps avoid sags. All the best from Jeff.
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Old 22-05-2008, 05:57   #5
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We had gelcoat repair kits from the factory for the touch up of scratches and small gouges on boat. It was almost stiff enough to not sag. Gelcoat works best if you can keep the air away from it while drying. The trick we used was kitchen wax paper.
Clean the area with acitone, mix your gelcoat with the hardner and apply to the area. Smooth out the gelcoat with a piece of wax paper over it and allow for the time to harden. This, if done properly keeps it from sagging and makes for easy sanding.

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Old 22-05-2008, 08:26   #6
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Yes you can use gelcoat. What Alan is refering to is that the common gelcoat will not cure in contact with air. In order to effect curing it is sprayed with a sealant (PVA Mold Release). Once cured the sealant washes off with water.

I wouldn't worry to much about sagging. Once cured you will be sanding the repair back starting with 320 wet/dry and finishing with 600 wet/dry. After that a buffing compound is used to bring it back to the original shine.

A more critical problem is matching the color of the gelcoat. If not done correctly, and there are tricks, your boat will look like it has the pox.

I would recommend going to Bennet Marine video and getting two DVD's there on cosmetic gelcoat and fiberglass repair. There are actuall three DVD's in the set but everything in the third is covered in the first two.
Fiberglass Repair - Bennett Marine Video

I've been doing a lot of repairs on my boat for gouges, stress cracks, and lamination voids.

On another note, the DVD's will show you how to use a small airbrush to apply the gelcoat for small repairs. I use one I got for $24 - perhaps your yard will let you use one of those. There is virtually no overspray.

Good luck and have fun.
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Old 22-05-2008, 09:24   #7
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Gell coat can be formulated with an air inhibitor (wax) that will rise to the surface after application. The gel then cures and you are ready to sand and polish. It's not tough to spay and refinish gel. Buy some and have at it. Fiberglass Supply (Surfboards, Windsurfers, Kayaks, Canoes, Boats , Autos and more)
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Old 22-05-2008, 09:30   #8
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I have seen other boats that have had dings in the gelcoat repaired and it still never looks quite right, at least not as good as original. I used to repair dings in my Hobie, and even with the original factory color, it still was not perfect. Also, there is a waxy substance you spray over gelcoat after applying that separates it from the air so it cures properly.

Old gelcoat is so difficult to deal with with respect to curing, color matching, and getting the surface back to a mirror finish that I would find some way to get an LPU paint sprayed on, even if you have to move to a different boat yard that allows spraying. Also, in my opinion, LPU makes for a much better finish in a number of ways than does gelcoat. You can do all your own prep work so that all the painter has to do is shoot the primer and the finish coat, which saves money.
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Old 22-05-2008, 09:50   #9
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First what I know, you can do gelcoat, use minicraft paste repair kit, Mini-Craft of Florida, Inc. - Inventor of the Aerosol Spray Gel-Kote. It's thick with wax placed in it and should work just fine for vertical surfaces. They can also do a computer color match on your gelcoat to exactly match your gelcoat if you have something like a plug or something you can send them (I put in an extra 30 amp shore power outlet and simply sent them the plug).

As to paint, how much does that cost per ft if you do the prep yourself?
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Old 22-05-2008, 13:30   #10
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Quote:
I've had great success applying gelcoat to exterior surfaces (hull) with both spray and brush and it's a routine repair job. What am I missing?
Are you sure you are not using a similar product formulated as stated above, called Flowcoat. At least that is what it is called here. Gelcoat is used as an inbetween coating in molds and flow coat is for exterior coating. Similar as in they are styrene based products, but different as in curing and one major, anti-sag (to a point) products. However, at lest in my opinion, flow coat is not as good as the paint technologies now available, and personally I don't see the point of using the flowcoat product anymore.
What one gets in a repair kit is usually flow coat.
I have never heard of spraying a wax over the gelcoat to allow it to dry, but OK, that's a new one on me.
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Old 22-05-2008, 13:51   #11
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Originally Posted by Alan Wheeler View Post
I have never heard of spraying a wax over the gelcoat to allow it to dry, but OK, that's a new one on me.
That's pretty much standard practice up and over on this side of the world. There are two ways to attain a cure with air-inhibited gelcoat - a liquid wax that is mixed with the gelcoat and a liquid polyvinyl alcohol that is sprayed over the gelcoat. The wax rises to the surface when the gelcoat is applied and blocks the air, and the PVA simply covers the gelcoat and is easily washed away with water after cure. You can even buy gelcoat with the wax already added.

Gelcoat paste is available for no-sag repairs. See here for an example (#355): http://www.lbifiberglass.com/POLYGELCOATS/polygel.html

You can also thicken gelcoat with microballoons to fill gouges. Leave it air inhibited so that it doesn't cure completely, and then "paint" matched color gelcoat over it with a wax additive or PVA coat for cure. I find a Preval sprayer works great for these types of small finish repairs and allows you to feather the color out into the old gelcoat. They are inexpensive enough that I use them as disposable, rather than bothering to clean them out and reuse them. Preval Spray Gun - Home

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Old 15-06-2008, 17:29   #12
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Continuing the anti-sag gel-coat saga

Well. based on the recommendations, I have a plan plus some materials. The boat is in western Washington state, and it rained most of the time we were there, but we will be back in August to try this stuff. We went over to the new location of Fiberglass Supply (by the Burlington regional airport). They had been in Oregon for many years, mostly specializing in supplies for surfboards, ete, and using resin infusion. However, their catalog (printed on one side of paper) is about a half inch thick. They carry a lot of supplies, though not as much as Fiberlay in Seattle. So we found visiting them in person was worth our time. They have some reasonably technical hands on knowledge. Per the discussions in this thread, we got some Duratec thinner plus some Preval sprayer cans to go with the normal gelcoat / wax / MEPK combination. My plan is to smooth the filled areas (done last summer) with some 220 grit, wipe it with some styrene (a technique from a Don Casey book), and then give each fill area light spot spray with the gelcoat/wax/MEPK/Duratec with the Preval unit. The idea is to use a series of thin applications to eliminate the sagging. Each application will be allowed to set, and then get dewaxed. I am expecting some color mis-match (new white vs 27 year old white), and doing thin sprays may help blend the interfaces.
There is likely some optimum mix ratio between the available viscosity and thixotropy. I may play with this, but I am not inclined to get involved with a science fair project.
More to follow.
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Old 16-06-2008, 04:47   #13
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billr, on the Duratec, check with their web/ tech dept on mixing it with a gelcoat with wax in styrene solution added, so far as I know the're alternative process/material combinations & not recomended in the same batch, it may well be successful in the same "brew" but do some test to be sure. All the best from Jeff.
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Old 16-06-2008, 05:22   #14
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I've just completed a 70 sq ft repair of gelcoat on Cat Tales, my Tobago 35. I bought isophthalic gelcoat (more resistant to water intrusion) and a product called Air Dry. I matched the gelcoat with many many paint chips, then sent the correct chip to the gelcoat company. A good group in Atlantic Canada is OP Plastics. The Air Dry is wax mixed with a styrene solvent. After asking lots of questions here and elsewhere, and trying different things, I painted it on with brushes. The Air Dry is only put on the last coat, which should be painted on before the other two coats completely cure. More coats may be required to get the thickness required.

The process requires experimentation to get the right non-drip, reasonable potlife, with the variables being surface area being attempted, time to paint, temperature, and of course the amount of MEK hardner. The Air Dry amount should match the amount of hardner in the last coat.

There are no easy ways to get a smooth surface. I tried many ways, and finally settled on a flat dry-wall sanding board with handle covered with 400 grit wet-paper, with a spray bottle with water and a bit of soap. I kept sanding, spraying, and thinking about the Karate Kid. My wife sanded through in a couple of places, and as tough as it was, I fired her ;-). I touched these areas up with one more coat and finished.

I hope to buff it out this weekend.
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Old 20-06-2008, 16:37   #15
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Cheat on the color matching: paint the whole transom and feather the edges. Corners hide color changes.
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