Fiberglass Core Replacement Part 2

In part 2 of this series I cover the cutting and installation of the new plywood core for the upper helm. The materials used in this episode were:

West System Epoxy (105 resin and 205 hardener)

West System 403 Microfiber Filler

West System 404 High Density Filler

A general use guide for all of their fillers can be viewed HERE

I realize it may be a little confusing why I used certain fillers for one application and then another type of filler for a different step in the process.

When laminating the new core onto the fiberglass deck and filling the ‘Relief Cuts’ on the bottom side of the panel, 403 filler was used as it creates a nice thick paste that is ideal for making an epoxy “Bed” for the plywood to rest and bond to. Because of it’s thicker consistency it is able to fill and compensate for any un-evenness on the mounting surface, as well as fill the gaps left by the saw kerf. The thickness of this “bed” was roughly 1/8″ on each surface (on the plywood after the pre-coat as well as on the fiberglass mounting surface creating roughly 1/4″ thick bed when laminated) and was Ketchup consistency.

404 High Density Filler was used for filling in the small gaps that ran around the perimeter of the plywood which ranged anywhere from 1/16″ to 1/8″ wide. When this filler is mixed with the epoxy it provides a higher compressive strength to the resin while still remaining runny or a wet consistency. Because of this, it was able to flow down inside the small gaps and wet out / seal the edges of the plywood as well as fill this seam so that there were no air pockets or voids. If the gap around the edges of the plywood were larger (say 1/4″ or so) I could have used the 403 filler but given the relatively tight fit around the edge, the 403 filler would have been a little too thick to flow down and adequately fill the seam.

All of the materials used in this episode can be ordered through Jamestown Distributors

If you have any questions or comments on this video please post them below!!

Thanks for watching!


8 Responses to “Fiberglass Core Replacement Part 2”
  1. Russell Traina says:

    I need to do the same thing to my Catalina sailboat, to replace soggy core. I have seen some others replace it with this material that looks like it has small squares cut in to it. Exactly what is this material and where can I get it at?
    Thanks, Russell

  2. Lee says:

    Hi Andy, quick question …….
    When you sealed the plywood prior to replacing the cap …… What did you use to seal ?


    • ~Andy ~Andy says:

      Un-thickened epoxy 🙂 But, I should say that I’m only using epoxy for this project because I know that I will be painting (versus gelcoating). If I were going to be using gelcoat for the finished surface I would have used polyester based resins..

      Polyester resins don’t typically like to stick to epoxy surfaces. Other way around is fine, though 🙂 But, that’s for another video…

      • Nick says:

        Absolutely the best thing on the internet! I went from virgin to semi-ok in one day!
        Question: I have a small ski boat and want to epoxy then lay carpet what do you recommend for glue and prep after epoxy repairs. (sand then paint then glue? or just sand and glue? or any other method?)

        You rock the world!

  3. Jack From Denmark says:

    Hey Andy

    Great page you have here, and I love the way you explain things.
    Can’t wait to see more!
    One question:
    If you had to replace a core from the bottom, how would you do with the epoxy around the core?

    • ~Andy ~Andy says:

      To be honest, I wouldn’t do this from the bottom. Even though it seems like the easier route, it will take much longer and be a lot messier than trying to do the replacement from the top 🙂

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