How Do I Choose the Right Epoxy?

Discussion in 'Materials' started by CatBuilder, May 23, 2010.

  1. CatBuilder

    CatBuilder Previous Member

    More questions from the amateur here! :D

    I've had a short email with Raka Epoxy from the other thread. They have a new tropical epoxy that's coming out very soon. Do I want to be the first guy to try it when my life's savings and much unearned income is tied up in my new boat? I'm not sure I do, even though they are excellent with customer support.

    I have talked with West System. They say they won't blush, but don't try it with very high humidity.

    I have looked at System 3. I have been told to use MAS.

    Well, how do I select the proper epoxy for FL's climate?

    I will be building a composite boat in a tent outdoors, but it will have walls and possible humidity control. Hopefully, I can take Richard's advice and get an epoxy that will just work in the humid conditions in FL without any problems.

    I want to be able to put on all layers sequentially and not allow the epoxy to cure between coatings, even if this means hiring help for the hulls. When it comes to dagger boards and things, I can handle this.

    SO: I need a relatively short life in that I don't want it to take 24 hours to coat a dagger board with 6 coats of epoxy.

    Can anyone suggest any epoxy strategy here? How do I know what to buy? They all sound good (Raka sounds and looks good too, except I don't want to be the first guy to try it).

    The temperatures will be up to 98 degrees and 90% humidity in the summer. Down to to probably night time lows of 35 degrees in the winter. There will be a wide range of temperatures and humidities during this build.

    I am trying to buy my materials up front to save by buying in bulk. How do I go about this project? Which epoxy to buy? :confused:

    Sucks to be a newbie! :D
  2. hoytedow
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    hoytedow Carbon Based Life Form

    Humidity is worse approaching and after dusk, when the dew begins to settle. Once the dew burns off in the morning you should be good to go. Pick your spot and observe your natural surroundings for a couple of days before beginning epoxy work and you will see what I mean. Check condensation patterns on structures and vegetation.
  3. CatBuilder

    CatBuilder Previous Member

    Gotcha, Hoyt. I did check humidity charts. It shows they are highest in the morning, then trail off by afternoon.

    Here is the humidity graph for the area I'm building in:


    Here is the temperature graph:


    Given that either of the humidity or the temperature won't be a problem, I still don't understand what will make the best epoxy for my boat.

    Are they all the same??:?: :confused:

    How do I choose the best epoxy for a composite boat?
  4. apex1

    apex1 Guest

    You can only contact the suppliers and ask for their recommendation. Then do some tests.

  5. AndrewK
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    AndrewK Senior Member

    The starting point is with your designer, ask for the minimum mechanical properties required.
    Then get full mechanical data sheets from suppliers and make your choice based on facts not sales talk. Also get data for each hardener you plan to use in a system, do not assume they all produce the same cured product because they do not.
    I stay away from any supplier that can not provide this information no matter how good the prices are.
  6. Stumble
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    Stumble Senior Member

    I would also point out that in large construction slow or extra slow hardeners are desirable since they give you a much longer working time. It doesn't really matter if your rudder takes 24 hours to kick since it is just going to be resting after you are done, but making sure it doesn't kick in the middle of layup is a big advantage.

    On the other hand post curing is more desirable for slower mixes.

    Ah the trade offs begin early this morning.
  7. apex1

    apex1 Guest

    Interesting, so you stay away from ALL suppliers?

    There is no single mix on the market that fits all. And there is no supplier on the market who could give you a guarantee on properties in homebuilding.

    So, what is your approach? Leave it?


    btw. according to the last years invoices, we processed 713 metric tonnes of resins!
  8. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    You know well that the designer does not specify a formulation, and if you are not building in timber the designer will let you use PE or VE as well if they meet the requirements.
    Properties include HDT, elongation, tensile and compressive strengths.

    No I had no need to stay away from all suppliers, I chose the one that provided the information that allowed me to make my choice.

    And NO I was not asking for a guarantee, only data for the selection process.

  9. CatBuilder

    CatBuilder Previous Member

    You would think maybe someone has successfully built a composite boat in FL before? I wonder what they have used.

    Stumble (or anyone):

    You make a good point, Stumble. The hardener timing is also a concern I'm having. If you have a slower hardener, is the amount of time before it cures also slower by the same percentage?

    I mean, I am thinking I'd like to coat, then recoat, the recoat as quickly as possible without having to wait around between coats. Can I make a mistake and have a hardener that won't set up quickly enough to allow me to work at a normal rate? One where I'll have to sit and wait between coats?
  10. Submarine Tom

    Submarine Tom Previous Member

    These are pretty intense questions for a newbie.

    Perhaps you should get some experience before taking on such a large project.

    I would use fiberglas because that is what I know...

  11. apex1

    apex1 Guest

    You never will have to wait (except maybe on very small items), once the former layer has kicked (pot life is over), you can go ahead with the next layer.

    Slow hardeners generally need postcuring whithin a few weeks, just to remind you!

  12. CatBuilder

    CatBuilder Previous Member

    Excellent, Richard! I do believe I now understand enough about epoxy to begin some practice pieces. Thank you, everyone for your patience.
  13. apex1

    apex1 Guest


    ..and good luck (apart from skills).;)

  14. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    As you have done boat repairs as a business already you will know most of this.

    People have built many successful boats with all of the resins you mentioned and many others. The issue is not if they are fit for purpose but which best suits your requirement. You could in fact choose a resin and a single hardener say 30 - 45 minute gel time for the entire job, but of course most systems have a range of hardeners so that you can do a better job with more ease.
    In one of your other threads I think you mentioned that you want to charter this boat, if so I think you will find that you will have no choice but to maintain the humidity below 80% during lamination and cure, so the issue with blushing will not be as great as you imagine. Check with your local authorities.
    Your design is to reinforce the exterior with glass and only seal the interior with 3 coats of neat epoxy? I think you mentioned externally total of 6 layers, I assume this is only 1 or 2 of glass and the rest is neat epoxy?

    Lets say you have discussed with Kurt and he specifies following minimum properties;
    I will use SI units as it is easier for me.

    HDT 55'C, usually at least 15'C above service temperature
    Elongation 5%, good practice is for matrix to have larger elongation than the reinforcement but will also depend on the laminate strain design
    Tensile strength 55MPa, the higher the better
    Compressive strength 90MPa, the higher the better

    You then have to make choices on process conditions workshop temperature, humidity and whether or not you are going to use peel ply will determine how blush resisting a resin system is desired. Storage temperature, some resins will crystallize in low temperatures so you may have to provide some heat during winter or otherwise be forced to reheat until crystals disappear at regular intervals. Or choose a formulation that does not suffer from this.

    Workshop temperature, this will effect resin viscosity and gel time, reaction rate will double at approximately every 10'C rise in temperature. You have to deal with a wide range in ambient temperature so will need at least 2 if not 3 hardeners to match gel time with task at hand. If you decide to use some climate control say 20 - 35'C then 2 hardeners would do the job. Be aware that a 20 minute hardener will take approx 2 hrs to kick of when spread to a thin film. Viscosity, I find that a mix with 600 - 1000 mPas at 25'C works well in the 18 - 35'C conditions I work in. Its sufficiently thick enough not to drain out on vertical surfaces but thin enough to wet out the glass easily, but I do use peel ply and this helps to prevent drain out. If a mix viscosity is <500 at 25'C then you will have some drain out unless you start vacuum bagging. Above 1000 it starts to get harder to get a good and fast wet out.

    Curing conditions, are you only going to rely on ambient cure or are you prepared to post cure even at moderately low elevated temperature.

    If you decide on ambient cure only you may find that a number of resin systems will not meet a number of the above properties even though they are nothing special. Some suppliers may not even give you any or all the data, if not you decide if you are to keep them or delete them from your options list.
    You will find enough products that will meet the requirement with the exception say one property with one of the hardeners in the system.
    For example the resin system I use has 7 hardeners, I use the polyamide hardener for fairing (less toxic dust) and a fast and slow hardener for laminating. The slow hardener meets all of my mechanical requirements at long term ambient cure, the fast does not meet the elongation.
    Elongation with fast hardener is only 3% at ambient but with a post cure of 8hrs at 60'C this jumps to 6%.
    This simple example is the point I was making earlier on, by finding a supplier who will give you properties for all of the hardeners you plan to use be they good or bad allows you to make informed choices.

    Of course if you plan to post cure be it in stages as you go or at the end when all of the structural work is complete then almost all epoxies in the market will meet the above example.

    The resin properties required just for sealing the interior are not great, you want something that has the best water proofing ability and good impact resistance.
    Don't be talked into using the so called penetrating epoxies they are thinned down with solvents, this in fact compromises the water proofnes, all you need is a good surface coat. Tests have also shown that the extra penetration is only marginal. For example when infusing end grain balsa (which is probably most easily penetrated timber) with water thin infusion grade resins at 100% vacuum it is amazing how little the resin penetration is.
    What I recommend is a polyamide hardener for this job, its benefits are lower volatility and toxicity which is good when working inside confined hulls. It also has superior water resistance and flexibility that gives better toughness and impact resistance. It also has a much higher viscosity so that it will not sag on vertical surfaces as much.
    Down side is longer gel time usually around 45 minutes but this can be cut down with the addition of an accelerator if required. You still can get 3 coats on in a day at 25'C.
    Being more viscous one coat with this mix will be equal in thickness to two coats with standard laminating hardeners so your effort is cut down in half.
    The other thing I would recommend when doing this coating is to preheat the area before you start with your first coat so that the timber is warmer than the outside ambient temp. This will prevent the little out gassing bubbles that would otherwise form as the air inside the timber warms up.

    Regarding the major exterior laminating job, what Herman suggested in another thread is common practice and not compromised. But of course it is better to get it done in one hit. If you have four other helpers on the day, one mixing batches of resin the others laminating you will easily do the job in a 8hr day. Even so I would still use peel ply, I pay $1.25sqm and think it is worth the money in the whole scheme of things.

    I hope this is of use to you.

  15. apex1

    apex1 Guest

    I dare to disagree here Andrew. Doing the layup in one go, as I recommended from the very beginning, does not need peelply, it would be a complete waste of time and money.

    The rest of your comments were already handled in previous posts on the other threads. Unfortunately cat builder created several threads on almost the same topic.
    Low temp issues he will hardly have, building in FL, but humiditiy is a concern, though just to a lesser extend when the formulation is choosen right.
    And of course, all the slow hardeners (which he has to use in FL) will benefit from, or REQUIRE a post curing. But that was already discussed too.

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