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using foam as a mold

Discussion in 'Tech Tips and Advice' started by slaval, Jun 22, 2016.

  1. slaval

    slaval New Member

    I have a hole in the bottom of my wayfarer sailing dinghy right in the keel area, so I need a way to repair from the outside with the hull upturned. I need to form the keel shape for an maybe a foot in length, so I kind of need a mold.


    it looks like in the pic... except the hole is bigger now. That slither of fibreglass is gone, so its just one hole. I was wondering if I could maybe fill the hole with foam, sand or file it to the right profile and then use it as a base for laying glass cloth over. I am using epoxy and at the moment I have CSM cloth, but also I was wondering if perhaps I should get some woven cloth because that would be stronger, right? Anyway, my main question is - is the foam a good idea?, what kind of foam is best? I won't be able to get the foam off after because this part of the hull is the buoyancy changer and whilst it does have some access elsewhere, the access hatch is sealed shut. However, I don't think it matters, I am more concerned about getting a good strong repair. Any advice gratefully received.

  2. Martin @ EC Tech

    Martin @ EC Tech Tech Staff Member

    HI Sean, for this I would suggest getting someone to take a closer look on site preferable a marine surveyor to advise best course of action. I wouldn't feel comfortable unfortunately advising on this type of repair due to where it is. However I will try to look into this further for you and any information that may help I will forward in the next few days or so. Kind rgds Martin
  3. Martin @ EC Tech

    Martin @ EC Tech Tech Staff Member

    HI Sean, I have just had the following reply from our friends at West System hope this helps :-

    For this you would be best Laminating a backing support. This would be done by producing a splash moulding of the surrounding area that once cured can be posted through the letterbox hole and bonded in place to provide a backing to laminate against. This process is detailed in our Fibreglass boat repair and maintenance manual on page 19. The manual can be downloaded from our website via the link below:


    They should also ensure that the buoyancy chamber in dried out before the repair is done to avoid moisture being trapped in there.

    We trust this information meets your requirements and if you require any further information please do not hesitate to contact us.


  4. John Dickens

    John Dickens New Member Staff Member

    No boatbuilding experience so take this with a pinch of salt but if the contour of the keel is fairly consistent is it possible to take a mould from an adjacent keel section and use this mould to cover the damage as you laminate the repair from the inside?

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