I am a real beginner around fibreglass, epoxy and polyester. I have heard that there is a problem putting epoxy ontop of polyester or vice versa. Can anyone shed light on this issue?
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Allen
I'm no expert, but....
Colin, I'm sure others will correct me if I'm wrong, but it's my understanding that polyester is a good material to build with because it's cheaper than epoxy and offers adequate strength & rigidity for pleasure boat applications. For new construction, epoxy can offer a better end result but it's a lot more expensive & most boat builders don't offer epoxy hulls (though some do). As for repair work, I've been told that epoxy is a better choice because it has superior bonding properties. In other words, epoxy repairs will adhear to a preped surface better than polyester resulting in a more permanent repair. It's stronger than polyester, too. You'll notice that many products that get applied to a hull are epoxy based like many paints (1 part & 2 part) as well as barrier coats, etc. For that reason, I've been told that most people will prefer to build with poly but repair with epoxy. Any other opinions out there?? As I said, I'm not an expert on fiberglass repair, but I did do a keel/hull joint repair a few years ago with epoxy & some cloth & it's holding up great. I hope this helps! Allen Schweitzer s/v Falstaff C-30 Hull# 632
Colin, I'm sure others will correct me if I'm wrong, but it's my understanding that polyester is a good material to build with because it's cheaper than epoxy and offers adequate strength & rigidity for pleasure boat applications. For new construction, epoxy can offer a better end result but it's a lot more expensive & most boat builders don't offer epoxy hulls (though some do). As for repair work, I've been told that epoxy is a better choice because it has superior bonding properties. In other words, epoxy repairs will adhear to a preped surface better than polyester resulting in a more permanent repair. It's stronger than polyester, too. You'll notice that many products that get applied to a hull are epoxy based like many paints (1 part & 2 part) as well as barrier coats, etc. For that reason, I've been told that most people will prefer to build with poly but repair with epoxy. Any other opinions out there?? As I said, I'm not an expert on fiberglass repair, but I did do a keel/hull joint repair a few years ago with epoxy & some cloth & it's holding up great. I hope this helps! Allen Schweitzer s/v Falstaff C-30 Hull# 632
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Daryl
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Steve Christensen
Polyester over epoxy is fine
The idea that you can't put polyester over epoxy comes from failures where folks did not prep the surface properly, and tried to put polyester over epoxy surfaces that still had some amine "blush" present. Some of these amines inhibit the curing of the polyester, and you get poor secondard bonds. With proper surface prep it works just fine. Steve Christensen
The idea that you can't put polyester over epoxy comes from failures where folks did not prep the surface properly, and tried to put polyester over epoxy surfaces that still had some amine "blush" present. Some of these amines inhibit the curing of the polyester, and you get poor secondard bonds. With proper surface prep it works just fine. Steve Christensen
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Bill
I was under the same impression as Allen (+)
Epoxy can go over polyester fine, in fact it's supposed to be a preferred method for blister repair. However, no personal experience... Fair winds, Bill S/V "Ngemelis"
Epoxy can go over polyester fine, in fact it's supposed to be a preferred method for blister repair. However, no personal experience... Fair winds, Bill S/V "Ngemelis"
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robert taylor
be safe not sorry
i agree with steve. however, many boat yards will not put polyester gelcoat over epoxy. gudgeon company will tell you that it is fine, but there are a lot of horror stories out there that claim huge sections of gelcoat delaminated when put over epoxy (steve's theory about the amines may be the culprit). since you are relatively inexperienced, i would not recommend polyester over epoxy. even when sanding the epoxy, some of the amines can be embedded in the surface....it almost takes a chemical removal of the amines to be sure they are gone. but as stated here earlier, epoxy over polyester is great.
i agree with steve. however, many boat yards will not put polyester gelcoat over epoxy. gudgeon company will tell you that it is fine, but there are a lot of horror stories out there that claim huge sections of gelcoat delaminated when put over epoxy (steve's theory about the amines may be the culprit). since you are relatively inexperienced, i would not recommend polyester over epoxy. even when sanding the epoxy, some of the amines can be embedded in the surface....it almost takes a chemical removal of the amines to be sure they are gone. but as stated here earlier, epoxy over polyester is great.
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Gerry, Newbury MA.
Epoxy and polyester
The amine blush that results from cured epoxy is easily removed by washing with water and a Scotsh-Brite pad. Properly cleaned and prepped epoxy laminate can be top coated with poly gel coat with no adverse effects. However, putting epoxy on top of polyester that is fairly recent can cause adhesion problems since cured poly continues to out-gas for quite awhile after curing. Generally, for safety sake, if I can get a good whiff of polyester I use polyester. On older boats though this isn't usually much of a problem and I use epoxy on these for my repairs. Note also that regular mat strand cloth doesn't work real well with epoxy since it doesn't fully absorb the resin for complete saturation due I believe to the binders used to hold the strands together. If your going to use epoxy then you should use mat made for epoxy wet out to assure that you don't end up with a partially dry lay-up which can cause delamination problems down the road.
The amine blush that results from cured epoxy is easily removed by washing with water and a Scotsh-Brite pad. Properly cleaned and prepped epoxy laminate can be top coated with poly gel coat with no adverse effects. However, putting epoxy on top of polyester that is fairly recent can cause adhesion problems since cured poly continues to out-gas for quite awhile after curing. Generally, for safety sake, if I can get a good whiff of polyester I use polyester. On older boats though this isn't usually much of a problem and I use epoxy on these for my repairs. Note also that regular mat strand cloth doesn't work real well with epoxy since it doesn't fully absorb the resin for complete saturation due I believe to the binders used to hold the strands together. If your going to use epoxy then you should use mat made for epoxy wet out to assure that you don't end up with a partially dry lay-up which can cause delamination problems down the road.
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Windship
Epoxy over polyester
If you just used polyester in the first place, you wouldn't have to worry about it at all!! I said it on another string and I'll say it here; If there was a problem with using polyester for repairs, there would be a rash of failures all over the world but thats simply not the case. Dennis
If you just used polyester in the first place, you wouldn't have to worry about it at all!! I said it on another string and I'll say it here; If there was a problem with using polyester for repairs, there would be a rash of failures all over the world but thats simply not the case. Dennis
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Art Femenella
It's in the Prep
We use epoxies for wood window restoration. The amine blush must be removed for anything to properly adhere to the cured epoxy. If prepped right, it makes a very good bonding surface.
We use epoxies for wood window restoration. The amine blush must be removed for anything to properly adhere to the cured epoxy. If prepped right, it makes a very good bonding surface.
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