West System epoxy over D.E.R 331 epoxy

Discussion in 'Materials' started by bobbychuong, Sep 27, 2008.

  1. bobbychuong
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    bobbychuong Junior Member

    Hello everybody,

    I have just a plywood boat from a guy in my area, but it is not finished. It has been covered with the D.E.R 331 epoxy from Dow Chemical. As far as I know this epoxy is general purpose epoxy and it not suitable for boat building. Now I want to put on another coat to protect this epoxy from UV light and water and I think of the West System product. Can anybody tell if it's better to do this or I just use some paints over the D.E.R 331 layer?

    Thanks for reading
     
  2. marshmat
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    marshmat Senior Member

    Technical data sheet for the Dow D.E.R. 331 epoxy is attached.

    You are right that it is a general purpose epoxy, while West System is developed with marine use in mind. But it's better to base your comparison on the actual properties of the materials, than on what they're marketed for.

    Dow's sheet suggests that DER331 is suitable for "marine and protective coatings", among other things. Physical properties look generally comparable to West System, and it has slightly higher tensile strength and elongation at break. Flexural properties are very close to West System. Water absorption is 0.41% at 7 days, 1.7% at 120 days.

    So, based on Dow's TDS for the product, it doesn't look that unreasonable to me. As with most epoxies it is probably UV sensitive to some degree. But I think a proper marine paint job should take care of that.
     
  3. bobbychuong
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    bobbychuong Junior Member

    Thank you very much for your reply marshmat. I will send you some picture of the boat after I paint it.
     
  4. Jimbo1490
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    Jimbo1490 Senior Member

    DER 331 is Dow's 'basic' bisphenol-a resin, much like Epon 828. Every epoxy manufacturer makes this type of resin and they are all basically interchangable. West system is a (proprietary) blend of epoxy resins and/or reactive modifiers. Remember that West is not an epoxy manufacturer like Dow. Instead they are a formulator/re-seller of epoxy resins made by others, like Dow.

    Jimbo
     
  5. bobbychuong
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    bobbychuong Junior Member

    Thank you Jimbo1490!
     
  6. Herman
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    Herman Senior Member

    To get back to the problem:

    The boat is covered in epoxy now. This means it should get a coat of varnish, either pigmented, or transparent with a good UV filter. A 2K PU paint is recommended. (no idea what is available at your place)

    Re-coating the boat with West System Epoxy is not neccesary, unless the boat has received some scratches or dents. These should be touched up before painting the boat.
     
  7. GG
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    GG offshore artie

    Jimbo west system is made by dow along with there pro set epoxy . I think Dow is only 20 minutes out from west system's corporate headquater's :cool:
     
  8. Jimbo1490
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    Jimbo1490 Senior Member

    A very knowledgeable formulator told me based on his experience in wholesale epoxy sales/distribution having worked for all of the 'big three' (Shell, Ciba & Reichold) that West bought from whichever company could supply price/delivery terms they liked and that the contracts were not long term. After all, EEW 190 resin is basically a commodity item; it's all the same.

    Jimbo
     

  9. purvisgs
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    purvisgs New Member

    somewhat unrelated epoxy q's

    Maybe I should start a new topic, but it seems like there are several very knowledgeable users who may be able to answer my questions here already...

    (Concerning laminating vs "coating" epoxy, and what makes a "low temp" / fast hardener)

    1st question relates to two epoxies that are available to me surplus-
    philliclad 1775/ 60ts "protective shaft coating" (pot life 40min @ 72 F for 1 gal batch) one of the uses on the spec sheet is laminating/ FRP spec sheet here

    philliclad 6470 "high build heavy duty coating"
    (pot life 30 min @72 F) spec sheet here

    ** the mechanical properties for these epoxies seem very similar to each other (tensile and flexural strength), the only notable difference is that the 6470 product is gray colored.. looking at the ingredients 6470 (msds here) 1775 (msds here), hardeners have significantly different ingredients, resins are pretty much the same- could anyone possibly tell me about how the different ingredients in these 2 hardeners might affect the finished product/ etc?

    Question: could I use the 6470 product for laminating (non structural), if not, why not. The reason I am more interested in the 6470 product is the shorter pot life probably means that I may actually be able to get the shop warm enough for this to set up this winter...

    Also: tensile strength and flexural strength of both of these products are in the ballpark of half that of the WEST products. For non-structural laminating (ie decks) how much difference would this make? can not find info on water absorption but assume it would be acceptable as these are both underwater epoxies.

    Finally: any brief info or links to web sites/ discussion about what specifically makes a hardener "low temp"/ "fast cure" OR how adding extra hardener affects the finished mechanical properties of the epoxy.

    Sorry for the long drawn out post, thank you VERY much for any info or insight that you can provide
     
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