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Old 22-04-2013, 12:10   #1
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Epoxy vs Fiberglass

is there any reason to not use fiber resin instead of epoxy?

i mean... when laying up cloth, it is pretty straight forward as that is that fiber resin is designed for but what about when tabbing in bulkheads or mixing with silica (fiberglass powder) or repairing decks or bulkheads?

at about $150 for 105 and 205 (206 / 209) i could reduce my material costs by 60% for the glass work.

i am 'that guy' who thinks all wood needs to be treated. everything has a layer of fiberglass or a coat of epoxy and is painted before whatever the finish treatment is applied (sole, head liner, mahogany etc).

thoughts?

-steve
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Old 22-04-2013, 12:25   #2
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Re: epoxy vs fiberglass

For weeting out cloth will be fine , polyester is very thin and wet out cloth nice, for tabbing bulkheads i prefer epoxy, have better adesive properties and is stronger, almost all the repairs this days are made with epoxy , if you found West expensive for your budget try to found cheaper epoxy, here in the island i can get 1 gallon of epoxy + reactor for 45 $ , and is the same stuff as West system , no big diference, same for Microballons , Silica, etc.,Cheers.
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Old 22-04-2013, 12:25   #3
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Re: epoxy vs fiberglass

Steve. when you say fiberglass are you referring to the standard polyester resin ? fiberglass is the actual cloth , the resin is different polyester is the cheapest vinyl ester is a nice step up
an epoxy . most expensive if cost is your concern and strong secondary bonds are required vinyl ester maybe a good choice
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Old 22-04-2013, 12:27   #4
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Re: epoxy vs fiberglass

Polyester resin does not bond to cured Polyester resin all that well. Have ripped tabbing off the hull with relatively ease when doing modifications. It also doesn't bond all that well to other materials. Polyester resin is also not water proof. The newer resins are much better at resisting water intrusion and the delamination that results. It works fine for 'hot' laminating for hull and deck layups.

Epoxy is just an all around better material for bonding things together. It is also virtually water proof so doesn't have water intrusion issues.

I've quit using polyester resin entirely. Epoxy is just so much better for bonding things together.
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Old 22-04-2013, 17:06   #5
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Re: epoxy vs fiberglass

the waterproof bit is the only reason i need to just spend the extra $$ and keep using epoxy.

thanks for the input.

-s
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Old 22-04-2013, 17:31   #6
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Re: epoxy vs fiberglass

Epoxy resin does not work well with matt. Matt is held together with a binder that is soluable in polyester resin. So, it will not form well in epoxt resin. Also, you have to protect epoxy resin from sunlight because the U.V. will break it down. No type of resin will form a chemical bond after a cure of 48 hours. You have to abrade the existing surface before applying the new lay up. The two surfaces will have a mechanical bond only. Normally that is strong enough.

Epoxy resin is easier to manage beause it can have a longer pot life if you use a "slow" hardener. It is not so sensitive to ambient temperature. It is about 50% more expensive than polyester. Other than that, they both are worked about the same.
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Old 22-04-2013, 21:27   #7
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Re: epoxy vs fiberglass

Unless ya get Mat bound with epoxy resin, which while a bit more expensive is available. Keep in mind that Gelcoat will NOT stick to epoxy.
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Old 22-04-2013, 22:31   #8
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Re: epoxy vs fiberglass

I have read that gelcoat does not adhere to epoxy. why that is I do not understand I have done small repairs spring gelcoat over epoxy with no issues what are the technical aspects of this?
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Old 22-04-2013, 23:34   #9
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Re: epoxy vs fiberglass

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Originally Posted by Sam Plan B View Post
Epoxy resin does not work well with matt. Matt is held together with a binder that is soluable in polyester resin. So, it will not form well in epoxt resin. Also, you have to protect epoxy resin from sunlight because the U.V. will break it down. No type of resin will form a chemical bond after a cure of 48 hours. You have to abrade the existing surface before applying the new lay up. The two surfaces will have a mechanical bond only. Normally that is strong enough.

Epoxy resin is easier to manage beause it can have a longer pot life if you use a "slow" hardener. It is not so sensitive to ambient temperature. It is about 50% more expensive than polyester. Other than that, they both are worked about the same.
An old indian trick I learned is to thin out the epoxy just a little with MEK. It'll soak right into the matt fairly well. It just takes a little longer to cure.

Also the same with the first layer on wood. It helps it to bond to the wood much better, in my experience.
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Old 23-04-2013, 00:04   #10
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With epoxy, don't use matt, replace it with cloth. So you alternate woven roving with cloth for epoxy,while you alternate woven roving with matt for polyester and vinylester. Cloth is much stronger than matt, so you can recalculate the layup schedule resulting in a thinner, lighter laminate with epoxy.

The cellulose that binds matt falls apart immediately with epoxy, resulting in a mess. Also, matt does not add much strength to a laminate other than filler and to reduce print-through of the roving.
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Old 23-04-2013, 01:40   #11
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Re: epoxy vs fiberglass

West Systems thinks you can put gel coat or polyester resin over epoxy


WEST SYSTEM | Projects | Fiberglass Boat Repair and Restoration - Polyester over epoxy

http://www.westsystem.com/ss/assets/...2Polyester.pdf

They also say you can use mat, but the styrene binder does not dissolve so it is less flexible.

WEST SYSTEM - Projects - Chopped stand mat & epoxy
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Old 23-04-2013, 03:58   #12
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Re: epoxy vs fiberglass

Having a lot of prior experience with polyester I mostly used it to build my boat and consequently saved myself several thousand dollarpounds and - I firmly believe - ended up with a very strong, light and watertight vessel.

In some ways polyester is a more forgiving material than epoxy and despite what a lot of people say is more than up to the task if you use a high-quality resin. I used epoxy for certain structural elements and for my rudders and daggerboard - applications where the superior mechanical qualities of epoxy were of benefit. My hulls are polyester with several coats of epoxy high-build coat to achieve the 'waterproof' aspect everybody likes.

Both resins have their idiosyncrasies and it's possible to screw up invisibly with either (the previous poster who ripped tabbing of his hull hadn't found evidence of bad resin, he'd found evidence of bad building). Polyester needs a good key if laminating to a cured surface; epoxy needs to be mixed VERY well and the components measured accurately, plus it also needs a good key. With many epoxies a waxy residue forms on the surface during curing - if you don't THOROUGHLY clean this off you might as well be laminating with jam.
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Old 23-04-2013, 05:31   #13
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Re: epoxy vs fiberglass

I would agree, polyester is very forgiving compared to epoxy. Easier to mix, less fussy about accurate amounts. Lack of pot life control can be an issue in warm temps.

Less chance of being sensitised in my experience too.
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Old 23-04-2013, 07:14   #14
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Re: Epoxy vs Fiberglass

WEST has done a great job of convincing amateur boat repairers it is the best thing to use. The truth is it is not.WEST stands for Wood Epoxy Saturation Technique. It was developed for use with wood not fiberglass. Great marketing has made it very popular for a lot of repairs it is not really well suited for.
Let's look at some of the myths
Secondary bonding with Polyester is poor. This is not true and good prep no matter what you use is important. If properly prepared poly will bond just as good as epoxy. Epoxy is more water resistant, yes but most repairs are above the water line so this is irrelevant
WEST claims poly gel coat will bond to epoxy but if you read their test data it is highly biased and not a long term study. And look who wrote it. I might be included to believe an independent study.
Things to consider:
When using Fiberglass the binder for all weaves must be of the type for epoxy not poly. Special material is used with epoxy
Epoxy has poor UV resistance. This is important when making exterior repairs.
Personally I see little need to ever use WEST epoxy when making repairs on a Poly fiberglass boat. It makes little sense as the cost is high and in 99% of repairs the slightly extra strength is irreverent. It makes more sense to use the same material the boat is built with. You would not patch a steel boat with Titanium would you just because it is a bit stronger? Few professionals use WEST to repair boats so why should the owner want to do this? Because WEST has done a great job selling their product.
Yes I use WEST all the time but mostly when working with wood. Below the waterline I use vinyl-ester because in my mind it is more compatible with polyester. I will not argue epoxy is stronger or has better water resistance (NOT water PROOF) but in 99% of repairs I see no reason to use epoxy and several reasons not to use it.
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Old 23-04-2013, 07:51   #15
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Re: Epoxy vs Fiberglass

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Myth: Secondary bonding with Polyester is poor. This is not true and good prep no matter what you use is important. If properly prepared poly will bond just as good as epoxy.
[...]
I will not argue epoxy is stronger
So, does epoxy provide better bonding than polyester or not? I think epoxy shear strength is about 4 times that of vinylester (2,000 psi vs 500 psi) and that vinylester gets it's better properties because it has epoxy molecules mixed in.

I think the only negative to epoxy is it's price.

Here's a good read on it (from professionals): EPOXYWORKS
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