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  #11  
Old 06-23-2009
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Quote:
Originally Posted by TomKeffer View Post
You're on the right track.

It's easier to get a smooth surface if you pile the epoxy on a little proud, then sand down so it's slightly (very slightly) concave.
I need 10 mills for the gel coat, right? That seems like a lot. If the area being filled is concave, then the gel coat will be very thin at the edges of the hole. Will that cause it to fail?
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Old 06-23-2009
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J,
I think you want your gelcoat to be a little thicker than that. 15-25 mils. But, on a repair of that size, if you prep properly and finish level, you can hardly avoid getting the correct thickness -- or at least the thickness of what you already have on the boat. Here is a picture that may help illustrate. Sorry it is so crude.



That is where you should be prior to sanding the new gelcoat down. The new gelcoat, if you catch it soon after it is hard, will be much softer than the old gelcoat and it will be easy to sand it flush.

For small, unobtrusive holes, you may find that marine-tex is "good enough." It may also help you get started with a white pigment base on what you are trying to accomplish.

I like using PVA to overcoat the final gelcoat layer to exclude air during cure. It's really easy to remove. But, it's something else you have to carry around/store. You can also buy a wax additive you add to the last batch of gelcaot or you can buy regular and finishing gelcoat.

The gelcoat that west marine sells kicks REALLY fast. Good for small areas; not so good for larger areas or working in the heat. You can always speed up a slower setting gelcoat with a heater and/or more catalyst.... You might get enough thickness with gelcoat paste.
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  #13  
Old 06-24-2009
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Quote:
Originally Posted by dgr View Post
J,
I think you want your gelcoat to be a little thicker than that. 15-25 mils. But, on a repair of that size, if you prep properly and finish level, you can hardly avoid getting the correct thickness -- or at least the thickness of what you already have on the boat. Here is a picture that may help illustrate. Sorry it is so crude.



That is where you should be prior to sanding the new gelcoat down. The new gelcoat, if you catch it soon after it is hard, will be much softer than the old gelcoat and it will be easy to sand it flush.

For small, unobtrusive holes, you may find that marine-tex is "good enough." It may also help you get started with a white pigment base on what you are trying to accomplish.

I like using PVA to overcoat the final gelcoat layer to exclude air during cure. It's really easy to remove. But, it's something else you have to carry around/store. You can also buy a wax additive you add to the last batch of gelcaot or you can buy regular and finishing gelcoat.

The gelcoat that west marine sells kicks REALLY fast. Good for small areas; not so good for larger areas or working in the heat. You can always speed up a slower setting gelcoat with a heater and/or more catalyst.... You might get enough thickness with gelcoat paste.
Thanks for all the tips! One thing I am concerned about that i did not mention, the fiberglass in the cockpit is very thin, probably no thicker then the gel coat. Your picture made me think about that. The epoxy won't fill a deep hole with sides, its a hole that is much wider than it is deep. How does that impact it?
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Old 06-24-2009
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If the fiberglass is that thin, it won't support its own weight... How big are these holes??? I seriously doubt the fiberglass is less than an 1/8" thick at a minimum.
Quote:
Originally Posted by jarcher View Post
Thanks for all the tips! One thing I am concerned about that i did not mention, the fiberglass in the cockpit is very thin, probably no thicker then the gel coat. Your picture made me think about that. The epoxy won't fill a deep hole with sides, its a hole that is much wider than it is deep. How does that impact it?
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Old 06-24-2009
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I would've found access to the back and put a wad of 5200 on the back of the screws. Done.
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Old 06-24-2009
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Quote:
Originally Posted by sailingdog View Post
If the fiberglass is that thin, it won't support its own weight... How big are these holes??? I seriously doubt the fiberglass is less than an 1/8" thick at a minimum.
Oh it's probably 1/8 or so. I got the impression from his diagram that it was expected to be thicker.
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Old 06-24-2009
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There are two epoxy systems available to us, polyamide and polyamine. The polyamine systems will react/mix with a little moisture in the air and forms amine blush slime layer as a function of cross linking. The polyamide system manages to crosslink without is side effect. An example of ideal application is underwater epoxies, amine epoxies react with the water and are not suitable.
I was a strong fan of the West system, used it for yrs, had difficulty in finding it, local stores switched to MAS. I was quite vocal about not liking the change until I tried it. To gel coat over it still requires proper surface prep, just less amine blush to worry about. MAS is an amine based epoxy, Ive used the slow and medium hardeners without experiencing any blush. (They do market it as blush free)

Blush is a reaction of moisture and carbon-dioxide in the atmosphere with the hydroscopic nature of the " simple amine" compounds due to excessive free radicals that are present during the reaction/ curing process. (very common in the lower end epoxies) Cycloaliphatic diamines / Cycloaliphatic Amines are almost completely void of the free radicals that hydroscopicly react making them inherently the most stable to not forming "salts of amine carbonate" aka, blush, but this comes with a higher price tag. Another down side is that they have difficulty in being reactive at low temperatures.

Be wary of those that try to appear larger than life by attempting to make everyone around them appear smaller.
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Old 06-25-2009
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MAS says:
"10. What is BLUSH, and how do I remove it?

Blush may form over the fast mix MAS Hardener and MAS Resin. The MAS Slow mix generally will not blush. Blush is noticeable as a slippery film formed over the cured surfaces. It can be removed with warm water and a sponge (rinse and wipe)."

I read that as their system uses amines in the hardener and both hardners will blush. I further read the MSDS (COMMON NAME - Cycloaliphatic Amine) as containing amines. From our resident epoxy technician, epoxymoron, I understand that blush is caused by amines and any amine presence in the product will potentially cause blush. If it was me, I'd just assume that there was blush present and take the 10 seconds to rinse and wipe before I started sanding.
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