Question re: Semi permanent mold release problem

Discussion in 'Materials' started by dberr, Jul 25, 2007.

  1. dberr
    Joined: Mar 2007
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    Location: Toronto

    dberr Junior Member

    We have been working with a new hull mold for a 16 ft. RIB hull. We decided to use semi-permanent mold release to eliminate the time needed to wax the mold. We did a few small tests with the mold release and everthing looked OK. On the first hull we sprayed the gelcoat and waited for it to kick. About 90 minutes later we see areas of pre-release in the gelcoat before we have put any skin coat in!!! A short time later, one of these areas in the gelcoat cracks open. It was a very warm day when this happened, but our shop has pretty good ventilation. We removed the gelcoat and started again the next day. This time we got the skin coat in without any trouble, but with each layer of glass put in the hull we noticed the problem again. We have reduced the amount of MEKP used in an attempt to compensate for the warm weather we have had recently, but the problem kept occuring. We have followed the directions for the mold release, used the recommended wiping cloths, and run some tests before trying to build a hull. I don't know what I have done wrong and our supplier can only suggest that I should have used one coat instead of the three coats recommended in the instructions. Any suggestions?

  2. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    In this book...
    that these people sell...
    it says under
    The supplier doesn't sound like the person to ask. Call the manufacturer and see what they say.
    It sounds like the release is working real good and the gel is curing too fast and shrinking and pulling away. You might just have to be real easy (low catalyst, slow cure) for the gel and skin coat.
    You might also want to run the question in the "Fiberglass and composite " section in the boatbuilding part of this forum.
  3. dberr
    Joined: Mar 2007
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    Location: Toronto

    dberr Junior Member

    Thanks for the info Sam. It has been helpful. I have contacted the release manufacturer and should here from a technical sales rep in the next few days. I suspect that high shop temperature is the biggest part of my problem. I may have to work in the evening if the weather stays hot like this, i.e. 90+ deg. F in the shop, even with fans blowing all day. What do people do in the south who have shops with no air conditioning, use 0.5% MEKP??


  4. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    There are many types and styles of Semi perm release agents, they have different release properties for each type of application, if you use one thats too slick you'll get pre-release problems.

    The gel coat may have too short of a gel time though, so check with the supplier of each product.

    Using a fan to blow air onto the gel coat will help also, that is if you're applying it correctly.
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