Final word on vinyl ester vs epoxy for blister repair systems?

Discussion in 'Materials' started by bntii, Aug 26, 2007.

  1. bntii
    Joined: Jun 2006
    Posts: 731
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    Location: MD

    bntii Senior Member

    Hello,

    I have been trying to pin this one down and have perhaps been hearing a consensus which I do not like on materials selection.

    I am about to do a peel and layup on a polyester GRP boat below the waterline. The laminate is moderately degraded via hydrolysis and I intend to peel down to sound layers and build back up with biax fabric.

    I want to use epoxy.

    After spending some hours researching on the net I have found that the preferred material for this type of repair is vinyl ester resin. The stated reasons are greater ease of application in boatyard conditions while maintaining physical properties of the material. Epoxies are said to be hard to use and maintain properties in field conditions. The material is said to be compatible with polyester hulls while epoxies are not.
    What gives? Epoxies are my resin of choice and would at face value seem to yield the highest quality repair in that they provide the highest bond strength, high resistance to hydrolysis and in my experience are very simple to mix and apply.

    I think vinyl esters are used by repairers for the same reasons that polyesters are used in builds- they are relatively inexpensive, they are fast to use and familiar.

    One well know company stated that the Dow 8084 vinyl ester they used is the most expensive resin available with the highest physical properties bar none- barcol harness, tensile strength bond strength etc.. Further stating that remaining styrene in hull provides a higher strength primary-like secondary bond to vinyl ester that is superior to bonds which epoxies are capable of.......

    Is their attachment to material as blind as mine to epoxies.....?

    Following are some of the many statements about the choice between the two:

    "epoxies, if done well, offer much higher resistance to moisture but are less compatible with the original hull resin and are very costly and hard to work.",

    "We've been using the vinylester material since 1988," said Phil. "We were one of the first to use this material, and in the beginning it was hard to find. Vinylester has been very successful. We warranty our blister repairs for five years. While some of our early epoxy-based repair jobs had to be redone under warranty, we haven't had to redo a single vinylester job yet."

    "A number of the resin systems are well documented and supported by their manufactures. Not all of the available products are compatible. It is strongly suggested that products from one system not be mixed with products from another system unless thorough testing is first performed. Of all the systems available, the epoxy resin systems appears in theory to be the most desirable. It should be pointed out that epoxy systems require very controlled environments and rather precise techniques during application, which might turn out to be a very limiting factor when used in the normal boat yard environment. Vinylester resins have been gaining popularity as a barrier coating and as a resin for use in relaminating, due to their ease of working and their much reduced sensitivity to environmental factors, they appear to work very well in the boat yard environment but under laboratory conditions they do not show quite the outstanding characteristics of the epoxy resins. The failure rate of vinylester resins is at present by far the smallest of the commonly used materials making their use very attractive."

    "The selection of resins to make the repair is a matter of some controversy. Marty believes that as a general rule, it is somewhat inappropriate to mix epoxy resins with ester resins. They are chemically different, have different degrees of flexibility and different coefficients of expansion, so that especially for under water applications, Marty prefers to repair poylester hulls with vinylester resins. Epoxy resins seem good, and they have had some success with epoxy resins, but are more comfortable using ester resins with ester resins. (It sounds a little like the philosophy of not mixing metals.)"

    From above:

    "It should be pointed out that epoxy systems require very controlled environments and rather precise techniques during application, which might turn out to be a very limiting factor when used in the normal boat yard environment."

    Has this person ever used epoxy??
     
  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Either way can work and if done correctly both will last for a very long time. Epoxy is stronger and bonds better, plus more water resistant, but if someone is very familiar with polyester and VE, and has little or no experiance with epoxy, then the VE job may turn out better.

    If you want to use epoxy, then use it.
     
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