Method for glassing complex shapes

Discussion in 'Fiberglass and Composite Boat Building' started by spiritgide, Jan 9, 2012.

  1. spiritgide
    Joined: Oct 2011
    Posts: 7
    Likes: 2, Points: 0, Legacy Rep: 33
    Location: Kanasa

    spiritgide Junior Member

    I'm in the process of customizing a 24' bay boat. This includes changing most of the inner structure. The new console will have a head and substantial instrumentation. It includes some complex shapes, such as the arched riser that the windshield fits to. It's always difficult to glass compound curves, and many simplify their designs to avoid them for that reason. I've built custom glass boats and other products from scratch for a long time and I had developed some tricks to help, but recently found a new fabric that works like none I've ever used before. The combination of a method I've used for years and this fabric allows doing what would seem impossible, such as glassing a flat surface that has a dome or irregular shapes rising out of it and doing it in one piece, without darts or reliefs. Inside and outside corners included.

    This fabric is called a triple-plain weave. So far, I can find only one version of it- made by BFG industries, style 1597 and heavy at 38 oz. Not cheap either, about $25 a yard, 38" wide. But- saves an incredible amount of work and gets great results.

    I'm doing the tough parts of the console (top, instrument panel and control counter) each in a single piece of fabric. I'm covering the multiple contours without darts or cuts of any kind.

    Here's the way it's done:
    First- Cut the blank of material, and dry-shape it over the surface. This material will flex within itself to conform to a shape. You lay the fabric over the dry surface, then start to smooth it from the center out with your hands. When you come to a contour, you just rub the material into the contours, over and around it, massaging a little as needed. Then back down to the flat, and on to the next such obstacle. The stuff just lays there, tight to the contour. The yarns in the weave will adjust- stretching around, compressing, etc as needed. When you have it laid and shaped it dry as you want, you put some locating marks on it with a felt tip to indicate points you will want to hit later.

    The next trick is the resin process. Since the fabric is still loose, normal application of resin would displace it an have you working to keep the irregular contours tight with wet slippery resin in it. That is very difficult, and not necessary. This is where the method comes in.

    You will resin the sub-surface in parts, which keeps the fabric orientation in place. In my case, each panel is done in two halves.

    First- I put some weights (I used steel plates I had handy) on one side to prevent sliding and hold the sheet in place. Next, I folded the other half back carefully to expose the substrate. Some of the formed shape is lost as you do , but most of the yarn position changes that took place while shaping will be retained. That helps the fabric fit back later with a minimum of work.

    Next, I brushed a light coat of resin over the area to be bonded. The resin type is important, because you will let it cure to a sticky stage about like duct tape- past the point of wet transfer when you touch it. While polyester and vinylester resins do reach that point, their "sticky time" working window is short lived, and that's impractical. However, epoxy holds that condition for a couple hours. In my case, I'm using Aeromarine 300 resin from John Greer. It's almost identical to the System Three Silvertip I used to use, but half the price. In the current conditions, I'm getting the right sticky stage at 5-6 hours after application and the window lasts for about 2 hours. Timing varies with conditions, of course.

    When the surface sticky state is ready, the fabric is folded out into the sticky area and progressively worked back against the contours, starting in the center. Until you press it firmly, it will lift off if needed to re-position. Once the materials is back in place, all surfaces and corners are rolled to stick the fabric tightly into the semi-cured epoxy. At that point, leave it alone until the epoxy has completely cured. Then fold the other side back and put the adhesive coating on it and start another cure-to-sticky phase.

    When the entire piece is stuck in place and the sticky coat cured, you can wet out the entire piece.

    *** Adding a footnote. The same company makes a similar product they call double plain weave, which is lighter- about 24 oz per yard. I was told it wasn't as easy to contour as the triple, but I tried a cut of it to see, and it's almost as good with a lot less bulk and a lower cost.

    Here's some pics of the glass on the cured sticky coat, ready to wet out:

    This is one piece of material!

    This is the joint between the windshield mounting contour and the flat area, which needed to be pretty square- and is.

    This is a "T" intersection between the rim above the instrument panel and the windshield contour extension butting into it.
    Last edited: Jan 10, 2012
    1 person likes this.
  2. Herman
    Joined: Oct 2004
    Posts: 1,618
    Likes: 94, Points: 48, Legacy Rep: 1240
    Location: The Netherlands

    Herman Senior Member

    Amazing stuff. Nice find!
  3. Submarine Tom

    Submarine Tom Previous Member


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