Post Curing Epoxy

Discussion in 'Materials' started by SeaJay, Jun 4, 2009.

  1. Herman
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    Herman Senior Member

    Remember that epoxy needs a good postcure before it reaches optimum values.

    I suggest doing 2 tests:

    laminate a piece with some cloth, on a piece of glass. (use mold release...)

    Cut this laminate in 2 pieces, postcure one of them (can be done very roughly by putting it in an oven for 2 hours at 120 degrees C). Leave the other alone.

    Now sand the postcured piece smooth (the other piece probably only needs a scrub of scotchbrite to be smooth) and paint them black.

    Now expose them in the sun for a while. Very likely the uncured piece will display print through. Mechanically not a problem, but it does not look nice.

    This will tell whether the resin improves from a postcure, and if the Tg is high enough for boat exteriors. (I recommend a Tg of 80 degrees C minimum for boat exteriors, if the boat should be black, probably even more)

    As for epoxy info, a lot of very specific info will not be on the datasheet (like, what is the max temperature if I cure a 5 mm laminate in 35 degrees C starting temperature) but things like Tg and some mechanical properties are the bare minimum.
  2. rwatson
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    rwatson Senior Member

    Thats re-assuring - I have heard a lot about print through, and always assumed that it had less than satisfactory mechanical properties, nice to know.

    I know Sam Devlin stays away from dark colours on boats just to avoid print thru specifically.
  3. Ilan Voyager
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    Ilan Voyager Senior Member

  4. Herman
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    Herman Senior Member

    So true. Also heat guns do a very effective job. One of my customers has a 50x50cm oven, about 6 meters long, heated by a single heat gun, and reaches 120C easily.

    However, the bigger the project gets, the more you need to use large machinery, gas heaters (no kerosene) are best. A well burning gas heater produces hardly any CO, but massive amounts of CO2, which is just as suffocating.
    There are also indirect heaters, which use a heat exchanger, and these are more easy to use, all they produce in the oven is hot air. The rest (oily fumes, Co, CO2, whatever) goes out the pipe.

    Light bulbs are fine for smaller objects, but keep fans running to spread the heat.

    About print:
    This Sam Devlin could make dark boats, but then he might need to change the resin used, to get a higher Tg. And probably postcure in the mold, needing a higher Tg mould.
  5. Ilan Voyager
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    Ilan Voyager Senior Member

    Catbuilder, you're truly too anxious. Cool a bit, you're just making a small epoxy plywood cat, the simplest of epoxy uses as glue and super-varnish. Not a 30 meters race trimaran. It's simple tech, nothing big, nor complicated. You're not making composite parts for a fighter or rocket. Take it as it comes for your pleasure, the Raka resin is largely good enough for its use.

    Raka is right, the epoxy used for wood will cure every day as sun heat it. After full cure the epoxy will be totally stable. The common 127 does not need post cure, it has been designed by the formulator for simple home and small shop boat building. Only heating is needed to accelerate the full hardening if the temp is too low or to save time if schedule is tight. All epoxies need enough temp for full cure.

    My experience with Raka resin under the ferocious Mexican sun (110° F and UV 14) did not showed any problem of softening and no any print out, which is a problem of composite molded boats, not of a plywood boat, whose outside glass fiber is covered by at least 3 coats of resin, plus primer and paint.

    For sure nobody is fool enough to paint in black a boat, it will become an oven under the most timid sun. Always light colors for boats. Also good for security, with orange or yellow antifouling paint. A capsized boat with blue or green antifouling is almost impossible to find, that's the experience of the marine officer...

    For your panels use very slow hardener, prepare all your panels before with scarfing and place numbers, have enough people for coating and heat it simply with bulb lights placed in the cylinder mold under the panel for a night or 24 hours. Do not forget that light plywood can soak a lot of resin, so make some trials before to know the amount of resin needed by square foot to get reliable joints, it's not complicated. Dry and starved glue joints are the most common mistakes. Like sex, guitar, horse riding, welding and a lot of human activities a bit of practice is needed for best results...

    I have used the Raka resin with satisfaction (free advertisement), and I've used a few tons of different epoxy resins (surely more than 500 metric tons) from different providers (West, Sicomin, Hexcel, Ciba Geigy...) in France for high tech composite race boats, warships, "low tech" plywood epoxy professional fishing boats, strip planking boats, etc... so I have an idea of epoxies. That the naval engineer and builder who talks.

    Raka sells resin since a long time (I've bought first time in 1997) and it's in the same range of quality as West System and System Three, all honorable providers. If the product was s... like the products sold by some sellers in Ebay, they wouldn't have lasted in Florida, place full of boatbuilding products providers, and lost all their pro customers.
  6. Ilan Voyager
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    Ilan Voyager Senior Member

    Very right, but a big oven with indirect heating it's a pro and expensive tool. Ok if you have enough production (like infusion resin), not for a small one off project...All that is pretty expensive.
  7. Herman
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    Herman Senior Member

    Here we have: "Andrews, heat for hire". Guess what their business is... I am sure they have collegues all over the world. Actually the Andrews company is from the UK.

    An oven is basicly an enclosure for hot air, and can be made with some PVC pipe or wooden battens, some plastic, and perhaps some bubble wrap.

    It can all be make-shift materials.
  8. CatBuilder

    CatBuilder Previous Member

    Or, in my case, it is the tent I'm already building in that reaches 48-50C without a problem when closed in the summer sunshine. Some fans and supplemental heaters should work well in it.

    Ilan Voyager: I really appreciate your posts. They have been very helpful. So you have the whole story, I'd like to explain why I am anxious:

    This boat building project represents about 2-3x my net worth. Yes, my net worth, not just savings. It relies on 3 years of unearned income my wife is earning while I build.

    This boat is a new charter boat for us. We will derive 100% of our income from this boat for the next 10 or 20 years. This is our business and our sole source of income once she's put into charter. Also, the boat is our home.

    Also, on a much more serious note (yes, it gets more serious): There is a big change happening in our country right now. The States used to have a wonderful thing called "middle class." This meant you could afford a house, 2 cars, possibly the wife might not work, children, education, health care and a pleasant life. This type of class in our country is vanishing at an alarming rate. My wife and I are exactly on the cusp of falling into the "lower class", which is a life of working at McDonald's, no health benefits, no way to purchase a house, no way to raise children without state aid. Many of our peers have already fallen into the new "lower class" out of the middle class.

    This boat building project is the way out of the serious problem. If it were to fail, we would not be able to try again. This is a "make or break" type of situation.

    Also, regarding Raka, many people on the forum told me I needed to have the data sheets on the epoxy to validate the use of it. Data sheets are not available. Some of my anxiety comes from the fact that you say the epoxy is great, while at the same time, they don't have data on it. Why does this make me nervous? See the last few paragraphs again.

    Does this make sense now?

    Boat building is not a wonderful hobby for me. It's a job to get me a charter boat I could not otherwise afford. I'm well educated, so I know I can do this correctly, given all the facts. Trouble is... the facts are few and far between regarding much of the materials involved in boat building.

    My catamaran is 13.71 meters x 7.62 meters. It might be "small" to you, but to me, it's a pretty large boat to build.

    I wanted to say all of this so you know I am not anxious for no reason. There are a lot of reasons behind the anxiety. I need the boat to come out perfectly (structurally). I cannot afford mistakes.

    Thank you very much for all of your input. The posts have been very helpful. Maybe now, you can see where my anxiety comes from.

    Ok, not to get too political, but here are some stats supporting my reason for building. I am pasting in an article. This is a very real situation. Anyone saying this isn't a real situation has inherited money, land or has started their life before mine. For my age and lower, this is a very real problem (as well as for some people who are retiring or out of work):

    The Middle Class in America Is Radically Shrinking. Here Are the Stats to Prove it
    Posted Jul 15, 2010 02:25pm EDT by Michael Snyder in Recession
    Related: ^DJI, ^GSPC, SPY, MCD, WMT, XRT, DIA
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    From The Business Insider
    Editor's note: Michael Snyder is editor of
    The 22 statistics detailed here prove beyond a shadow of a doubt that the middle class is being systematically wiped out of existence in America.
    The rich are getting richer and the poor are getting poorer at a staggering rate. Once upon a time, the United States had the largest and most prosperous middle class in the history of the world, but now that is changing at a blinding pace.
    So why are we witnessing such fundamental changes? Well, the globalism and "free trade" that our politicians and business leaders insisted would be so good for us have had some rather nasty side effects. It turns out that they didn't tell us that the "global economy" would mean that middle class American workers would eventually have to directly compete for jobs with people on the other side of the world where there is no minimum wage and very few regulations. The big global corporations have greatly benefited by exploiting third world labor pools over the last several decades, but middle class American workers have increasingly found things to be very tough.
    Here are the statistics to prove it:
    •*** 83 percent of all U.S. stocks are in the hands of 1 percent of the people. 
•*** 61 percent of Americans "always or usually" live paycheck to paycheck, which was up from 49 percent in 2008 and 43 percent in 2007.
•*** 66 percent of the income growth between 2001 and 2007 went to the top 1% of all Americans.
•*** 36 percent of Americans say that they don't contribute anything to retirement savings.
•*** A staggering 43 percent of Americans have less than $10,000 saved up for retirement.
•*** 24 percent of American workers say that they have postponed their planned retirement age in the past year.
•*** Over 1.4 million Americans filed for personal bankruptcy in 2009, which represented a 32 percent increase over 2008.
•*** Only the top 5 percent of U.S. households have earned enough additional income to match the rise in housing costs since 1975.
•*** For the first time in U.S. history, banks own a greater share of residential housing net worth in the United States than all individual Americans put together.
•*** In 1950, the ratio of the average executive's paycheck to the average worker's paycheck was about 30 to 1. Since the year 2000, that ratio has exploded to between 300 to 500 to one.
•*** As of 2007, the bottom 80 percent of American households held about 7% of the liquid financial assets.
•*** The bottom 50 percent of income earners in the United States now collectively own less than 1 percent of the nation’s wealth.
•*** Average Wall Street bonuses for 2009 were up 17 percent when compared with 2008.
•*** In the United States, the average federal worker now earns 60% MORE than the average worker in the private sector.
•*** The top 1 percent of U.S. households own nearly twice as much of America's corporate wealth as they did just 15 years ago.
•*** In America today, the average time needed to find a job has risen to a record 35.2 weeks.
•*** More than 40 percent of Americans who actually are employed are now working in service jobs, which are often very low paying.
•*** or the first time in U.S. history, more than 40 million Americans are on food stamps, and the U.S. Department of Agriculture projects that number will go up to 43 million Americans in 2011.
•*** This is what American workers now must compete against: in China a garment worker makes approximately 86 cents an hour and in Cambodia a garment worker makes approximately 22 cents an hour.
•*** Approximately 21 percent of all children in the United States are living below the poverty line in 2010 - the highest rate in 20 years.
•*** Despite the financial crisis, the number of millionaires in the United States rose a whopping 16 percent to 7.8 million in 2009.
•*** The top 10 percent of Americans now earn around 50 percent of our national income.
    Giant Sucking Sound
    The reality is that no matter how smart, how strong, how educated or how hard working American workers are, they just cannot compete with people who are desperate to put in 10 to 12 hour days at less than a dollar an hour on the other side of the world. After all, what corporation in their right mind is going to pay an American worker 10 times more (plus benefits) to do the same job? The world is fundamentally changing. Wealth and power are rapidly becoming concentrated at the top and the big global corporations are making massive amounts of money. Meanwhile, the American middle class is being systematically wiped out of existence as U.S. workers are slowly being merged into the new "global" labor pool.
    What do most Americans have to offer in the marketplace other than their labor? Not much. The truth is that most Americans are absolutely dependent on someone else giving them a job. But today, U.S. workers are "less attractive" than ever. Compared to the rest of the world, American workers are extremely expensive, and the government keeps passing more rules and regulations seemingly on a monthly basis that makes it even more difficult to conduct business in the United States.
    So corporations are moving operations out of the U.S. at breathtaking speed. Since the U.S. government does not penalize them for doing so, there really is no incentive for them to stay.
    What has developed is a situation where the people at the top are doing quite well, while most Americans are finding it increasingly difficult to make it. There are now about six unemployed Americans for every new job opening in the United States, and the number of "chronically unemployed" is absolutely soaring. There simply are not nearly enough jobs for everyone.
    Many of those who are able to get jobs are finding that they are making less money than they used to. In fact, an increasingly large percentage of Americans are working at low wage retail and service jobs.
    But you can't raise a family on what you make flipping burgers at McDonald's or on what you bring in from greeting customers down at the local Wal-Mart.
    The truth is that the middle class in America is dying -- and once it is gone it will be incredibly difficult to rebuild.
  9. fg1inc

    fg1inc Guest

    CatBuilder, you are obviously astute and well aware of the disappearring middle class in America. You have the ability to research your dream and carry it out. But I must ask.....where will you find this dream charter situation? I hope you understand that there are many people already in that business. And they too, are suffering. They probably are not going to welcome another charter operation in their area. And they won't be any too kind about it. I hope you will research this part of the dream as well as you are researching the construction of the boat.
    Fair winds and full sails to you.

  10. CatBuilder

    CatBuilder Previous Member

    Thank you for the kind tip. I have already done charters and have a special marketing strategy that sold our last boat out entirely, to the point of our exhaustion. It's not a dream charter situation, but a hopeful repeat of our past success in this industry.

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