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Old 21-12-2009, 11:54   #16
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Is there any truth to the story that if you use epoxy on a boat and in the future you come to do a repair using Polyester the fibreglass resin will not stick to Epoxy. If so how can you tell if you are trying to work on something that has Epoxy or Polyester resin?
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Old 21-12-2009, 12:07   #17
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You can epoxy onto polyester but you cannot put polyester on epoxy it will not bond. You can tell by experience but polyester and vinylester have a different feel and look. Epoxy has a high elongation (it is more flexible) Not sure how to explain it but someone used to working with the materials will know. Might have to sand it a bit to be sure.

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Old 21-12-2009, 14:05   #18
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Sergy,what sailvayu stated is largly right on,however polyester will in fact stick to PROPERLY PREPARED epoxy,but i cant think of a good reason to do so as its bond will not be great,use epoxy over epoxy or polyester or vinylester,use polyester or vinylester only over the same. Preperation is everything when working with ANY resin or adhesive, as a matter of fact when Roy M said that polyester wont even stick to itself what he failed to point out is that the same is true with epoxy if you dont do proper prep,some epoxies such as West produce a lot of amine blush when curing under certain circumstances,if you go ahead the next day with another layer it wont stick properly at all. So how do you know if something was made with epoxy or polyester / vinylester? Smell,thats the easiest way i know of,if you sand or cut the item and get a whiff,you will need to develop a nose for it bygetting hold of some known samples and sanding them,then it will be obvious.Hope this helps.
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Old 21-12-2009, 15:26   #19
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Thanks again guys
The reason I ask is if doing repairs to bottom of hull and there may be a possibility that the former owner did some blister repair using epoxy and I come along and use polyester resin it most likely will not stick. Being ignorant of the different texture or smell I probably should automatically go for the more expensive Epoxy just to be sure.
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Old 21-12-2009, 17:15   #20
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Sergy,you have the right idea,you are best using epoxy for below the waterline anyway.
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Old 21-12-2009, 17:30   #21
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You pays your money and takes your chances. I prefer epoxy to polyester, and one may make whatever choice they wish. But no whining later.
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Old 21-12-2009, 18:39   #22
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Polyester has a hard time sticking to itself. Pay extra - go epoxy. You will thank yourself many times in the future.
Actually, the greatest advantage to working in polyester to my mind is that it does stick to itself without sanding. You can layup a layer of glass then come back later and add more layers or fillets, gussets, whatever as long as you didn't add wax to the mix. Epoxy requires sanding between coats unless you catch it while it's "green".

While it's true that epoxy is superior in almost every regard, I find polyester easier to work with (others may prefer epoxy) and in the PO's application polyester will be fine. In fact, I have a dim memory of reading somewhere that Divinycell was formulated to work with polyester.

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Old 21-12-2009, 19:29   #23
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The greater percentage of fiberglass boats out there are constructed from what the industry calls "E-glass", orthothalic polyester resin.

If the shipping is reasonable for your location, do yourself a favor and go to LBI: http://www.lbifiberglass.com/CATEGORY/category.html and laminate your foam core with polyester resin and fiberglass cloth, surface with polyester fairing compound and finish with gel coat or LPU paint.
All you will do in this case is and save a bunch of money over the typical retail epoxy. LBI supplies the pros and weekend warriors with whatever you need and even has a simple formula for calculating how much product required. You can even get epoxy from them if you should desire.

Regarding structural integrity, (Strength) What I don't think I've seen mentioned here is that more importantly than what material you choose to laminate with, is the schedule of laminate (Number of layers), type of cloth chosen, quality of prep, quality of wet out, etc. In other words you can have strong or weak epoxy or polyester construction.

To that end before you start your final glassing for the sea hood you might want to consider your strength requirements, I.E. do you need to mount gear on the hood, do you want to stand on it on occasion, etc, etc, etc and then choose a laminate schedule that will accommodate your requirements. My personal outlook is that it takes less work in the long run to overbuild, Good luck!

P.S. ask for Deb in sales she will hook you up.
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Old 21-12-2009, 22:28   #24
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I don't suppose any discussion might include strength to weight ratios coupled with mass above the waterline? Keep it strong, keep it light. Keep the weight for stores and booty, and keep it low. Or don't. Throw some more ballast into her to keep her from going over because you wanted it to be really, really solid fiberglass in that deck and cabintop. Do what you're going to do and then own up to the behavior of your vessel once you get her in a seaway. Sadly, it's much more difficult to take off dead weight than to avoid putting it on in the first place.
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Old 22-12-2009, 07:18   #25
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All things being equal, the strength to weight ratio poyester vs. epoxy in this application a non issue.
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Old 22-12-2009, 23:04   #26
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So Roy,please inform us how much weight you expect to save on this sea hood and where in the laminate you expect to make this saving,then run a cost/benefit analysis for us.
Thanks,Steve.
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Old 23-12-2009, 08:28   #27
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So Roy,please inform us how much weight you expect to save on this sea hood and where in the laminate you expect to make this saving,then run a cost/benefit analysis for us.
Thanks,Steve.
Priceless Steve!
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Old 23-12-2009, 09:38   #28
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Sure folks! I'm happy to oblige with such serious considerations. How many layers of what weight cloth did you propose to cover the canopy with? Please include the additional cloth for the radius edges, assuming you follow the usual fabrication guidelines. I'll also assume you use fairly lean resin to glass ratios. Then, of course, I'll assume you have sanded off enough of the finish to assure a fair curve and cosmetic base, so you don't have to apply too much Bondo to cover your low spots. Will you be applying a final gelcoat to that base, or will you rely on an epoxy primer?

Folks, get real here. If you wish to be trivial, that is your right. If you wish to discuss the cumulative effects of excess weight caused by construction techniques that substitute mass for strength, then do so. Any of the knowledgeable folks on this forum will support the concept of keeping excess weight, especially above the waterline, to a minimum. Any experienced builder will recognize the tradeoffs of cost versus consequence, with respect to strength, durability and weight. A hatch is a simple issue. But, as many of you may have observed, some folks will often follow a pattern of decisionmaking in boat construction using the credo "a little more won't hurt". How many of you have seen the boat interiors built of massive oak, the decks and cabinsides built to resist bullets with "just a few" more layers of glass and polyester. The list of construction oddities where weight is seemingly disregarded may be endless. Of course a hatch, especially of Divinycell, is inconsequential in mass. The point, which apparently is too meaningless for some, is that many builders and sailors understand the consequences of keeping useless weight to a minimum, especially above the waterline. Then there are others who simply never think about the concept. And there are those who simply reject the concept in the first place. The latter group get to accept full responsibility for the heavy rolling and poorer performance their craft exhibit. The ones who are ignorant of the concept may be lucky and learn otherwise, then make consistent attempts to shave the pounds where they can. The first group already gets it and has spent the time and money to use the materials that provide the highest strength to weight ratios within their budgets and reason. All of us come to this game knowing nothing. Some of us make mistakes and learn from the consequences, constantly seeking new options. Others, perhaps seeking something else, choose to be independent and free thinkers, remaining unfettered by mere experience or the "laws" of physics. There might be a parallel here between the lumbering, top-heavy craft that remain at the dock versus the ones that venture over the horizon, hull down and rising to the next wave. The bottom line is the owner who wittingly allows excess top weight to accumulate owns the full responsibility for the sluggishness of their vessel. The builder that adds it for an unwitting owner, shares the responsibility. The one who keeps the strength to weight ratio uppermost in their consciousness is the beneficiary.
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Old 23-12-2009, 11:52   #29
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I have built and shaped a sea hood out of divinycell foam. I now need to cover it in several layers of fiberglass. I notice that polyester resin is substantially cheaper than epoxy resin. Is there any reason I canít use the polyester resin for this job?

Also does any one know how to calculate how much resin i will need?

thanks
Roy, if anyone here is being trivial itís you! As usual you are way off point. The original question is asking if polyester resin is suitable for glassing over a foam cored sea hood and asked absolutely nothing asked about strength to weight ratios or any other of the inane gibberish you feel compelled to espouse in your multi paragraph rant. The answer to the original posters initial question is a resounding yes that polyester resin from many perspectives would be the choice.

Rather than present an answer based on good industry accepted practices for the job at hand, you decided to chastise and warned us if we didn't follow your misguided, financially and productivity inefficient recommendations that:

(Arrogant quote) Ē ďDo what you're going to do and then own up to the behavior of your vessel once you get her in a seaway.

Are you really suggesting that for a given laminate schedule in glassing over a sea hood that amounts to a couple of square feet that the difference between the choice of epoxy vs. polyester resin will adversely affect the boats handling?


I have to go do some last minute holiday shopping, my kids won't think it's "trivial" if santa doesn't deliver the goods. Peace on earth and happy, healthy holidays to all.

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Old 23-12-2009, 12:52   #30
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Come on guys lets play nice it is the holiday season lets show some good will towards our follow man lol. Roy makes a couple of good points and it is does not hurt to remind folks that keeping weight down is a good thing. And Roy you need to be open to other materials than just epoxy like I said before right product for right use. All good designers and engineers keep all the concepts everyone is talking in mind. Lets face it in the world of boats you ask 10 different people the same question and you will get 10 different answers, 9 of which are likely right just different.

Now lets have some eggnog and rum and be merry

Fair Winds
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