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OT- fiberglassing .001

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  • OT- fiberglassing .001

    Done bits here and there on my fiberglass cargo container. Yesterday I got into the process of separating the mold from the container. As some of you may recall, I used something like Pam as a final mold release agent, and a previous test showed it would work. Murphy paid me a visit, and now here I am, 7 solid hours of work later, with about 10% of it left to be removed. I'm tired of this chiseling, gouging, scraping, soaking, itching-

    Moral of the story- one should always use a proper mold release agent.

    Project is coming along though, and once again I'm impressed at how tough a fiberglass structure can be.

    I do have one question, and it involves metal- two of my mounting points will be a fiberglass arm bolted to an aluminum boss, which is basically about 3/4 inch in diameter. Minus the bolt hole, that leaves basically a lip about 3/4 diameter and 1/8 wide to bolt the glass arm to. That part of the arm has lots of area, so if I can I'd like to spread the mounting force into more of that area. I can epoxy a washer to the side where it meets the mounting boss, or I could consider something like a grommet applied through an enlarged hole in the glass arm, kind of like a rivet with a hole through the center. Not sure if that would improve anything- on the outside the bolt holding this point is also bolting the rear foot pegs on, so there's a significant area of metal at that point.

    This makes me wonder about ways to fasten stuff to fiberglass structures. You don't want to create small, high load areas in the glass, which might start to cause cracking and weakness. Where loads are high, I'm thinking it might be a good idea to bond in a fastening point of some sort. So far, all I've seen in this regard is bolts and washers, which still puts a lot of force on the small area around the bolt hole.

    Where you may have more than one bolt, you could use a plate behind it, drilled to suit. For just one bolt- just a shop-made thicker and larger washer?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    I have bedded many rifle actions, using fiberglass and JB weld, and the only release agent I have ever used is Johnson's Wax, the same old stuff mom use to put on the floor, and I have never had a problem.



    • #3
      There are a couple approaches for strengthening (other than multiple layers of glass) used in home built fiberglass aircraft. Where force is large the nut is welded to thin stainless plate, area typically a couple square inches, with 2 or more layers of glass on each side. (The nut has wax pushed in to keep the epoxy from filling the threads.) Sometimes the plate is drilled with many holes to improve grip.

      When there is lots of area and less force then thin aircraft plywood is used to spread the load.

      When you expect to do a second layup then "peel-ply" is used - this is a tightly woven dacron cloth tape which is laid over the join area and squeegee'ed down (leave an end loose for removal). After the epoxy cures the peel-ply is pulled off - epoxy doesn't stick to it well and it is strong cloth. This leaves the weave of the cloth imprinted on the work so the subsequent layer can get a good grip and it eliminates sanding prior to the second layup. Forgetting to remove the peel-ply prevents a good subsequent bond and has caused bond failures and fatalities...

      A fringe benefit of using peel-ply is that it removes the sticky layer that generally forms on the outside of layups. This layer can reduce the strength of the bond to the second layer so it is often removed by sanding where the roughened surface improves the grip of the second layer. Unfortunately, this outer layer generally contains chemicals that can sensitize one to epoxy, especially when made into dust by sanding. Best to wash the layup with vinegar and water prior to sanding; the vinegar helps to neutralize the sensitizing chemicals.


      Edit: Aluminum items embedded in the structure should be anodized or treated with Alodyne to prevent corrosion.

      One-off items can be shaped from foam, then laid up with cloth and epoxy. After cure the foam is dissolved out, often using gasoline.

      Builder's plastic can work as a mold release for simple, mostly flat parts since epoxy doesn't stick to it. Useful when making two parts that should fit well and will be bolted together later.
      Last edited by GadgetBuilder; 07-11-2012, 09:42 PM.
      Location: Newtown, CT USA


      • #4
        I seem to recall from the distant past there was a sort of female insert that had a very, very coarse thread that could screw into the fiberglass but this was usually where a sort of boss had been built (either as part of the mold or built up after the fact). IIRC they look sort of like the fastener/insert used in take apart furniture (the stuff made of particle board).

        I also seem to remember something just the opposite sort of like a stud that had a coarse thread on one end that you molded in and it left a more common threaded portion sticking out.

        Neither of those were for any sort of real load though...


        • #5
          The company I work for installs architectural fiberglass panels. Often times the parts will have steel plates embedded between layers of fiberglass to reinforce the panels and allow bolts to anchor the parts.


          • #6
            Yes, you should always use a good quality mould release agent. Unfortunate that you have found this out the hard way. A good release agent isn't very expensive when you consider the cost of the mould, the part and your time if you have a stickup. On a new mould you should apply the release agent at least 5 or 6 times and then also use PVA ( )for at least the first few parts.
            Metal "bobbins" have been used for years in fibreglassing. Polyester resin doesn't stick very well to any metal and apparently stainless is one of the worst.
            If you use extra thickness of glass, make sure you have each succeding layer smaller in area than the one before it. This is so you end up with a tapered edge to the extra thickness to minimise stress points.

            There is a bit of interesting info at this site as well.

            A lot of the composite supply companys have lots of info on their sites.

            I'm not an expert in this, I did a, 2 year, fibreglassing course ar night school about 15 years ago so I could repair and rebuild the body on a fibreglass sports car that I owned at the time. Most of my experience with the car has been in repairing damage rather than making new parts though I have done a little bit of that, but not for a few years now.


            • #7
              Carnuba paste wax is normally what you apply to both seal the mold and smooth it up to a gloss. One site I went to suggested about five coats, allowing to dry and then buff between coats. The final coat is left to dry, but not for as long as all the previous coats. This is what is supposed to act as a release agent. That does work, but PVA releases easier and with no damage to the waxed surface. For repeat 'pulls' from the same mold, you would definitely not skip the PVA.

              In my case, I would have found it useful to be able to get about three pulls from the mold, but no matter now- the mold is now a chopped up mess covering the basement floor. My wax job was three coats, and that is enough to get the result I was looking for- but still, the mistake I made was using a release agent that was not compatible. More layers of wax would not have solved the problem. Had I not used the Pam-like stuff, and instead just applied the last wax coat per the instructions, I think I would have been ok.

              Doesn't matter now anyway, and I think I've learned my lesson (finally).

              As far as strengthening a bolt hole in fiberglass, the best idea I've heard so far is to add layers of cloth or matte, with each layer being a little smaller in size than the previous layer. With the end result being a sort of thickened bump where the bolt hole would be, it seems about the best way to get the strength without just transferring a potential problem to another spot. I just can't seem to feel good about laminating in a different material. If there was to be a captive nut or something, I'm ok with the idea of building up the thickness for strength, then laminating over the nut to keep it in place. Any kind of de-laminating or wreckage due to the nut having become too tight or seized, then spinning, will be surface damage and would not affect the strength or integrity of the fiberglass structure.

              In this project, there are two points where a captive nut would be a good idea- I find that I can't reach the inner point with the container in place, so I'm forced to resort to that. I'll just make those two nuts from steel, and make it with fingers so the fiberglass and resin will have the strongest control over it spinning loose.

              Where my foot pegs mount against the fiberglass arms, I think I'll apply some fresh resin and then mount them snugly, but not tight. I'll wax up the peg mounts first so they will be removable later, but the fresh resin will create a slight pocket around the mount and that will help keep it from moving around. Once the resin is cured, I'll make sure the bolts are tightened further. I'll also need to make sure the resin doesn't seize the bolts in place.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-