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OT - Fiberglassing - How to do it?

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  • OT - Fiberglassing - How to do it?

    While I know a bit about metalworking, I know almost nothing about fiberglassing.

    Could someone discuss the process, how to do it and to do it properly?

    Also I would appreciate links to sites that discuss fiberglassing similar to how HSM discusses metalworking.



  • #2
    Polyester resin is mixed with catalyst to create a reaction which cures the plastic.

    This mix is spread or poured onto the form or substrate you want to stiffen and that's also where you apply or have laid out the actual fiberglass (which can be woven or mat - even fiberglass insulation will work for reinforcing fibers).

    What's often called "fiberglass" in car stereo's isn't. They use fabric (often polyester as well) to hold the form, so there's no fiberglass in it.

    The polyester is there to hold the fibers in alignment and the fibers are what provide the strength. Really short fibers (2mm) will increase the stiffness and strength of the un-reinforced plastic by a very high percentage, so don't think you need long fibers to gain any appreciable strength. Long fibers are better, but short ones are still useful too.

    I like working with it, but it does create a lot of stink and heat. You can slow the curing down by keeping the mix cold. Re-application (additional layers) can be done at any time. Just scuff the surface if it's already cured.

    I've always used saran wrap as a release agent. The polyester won't stick to it. You can line a mold cavity with the wrap, fill the cavity, and then let it cure and the object just peels out of the saran wrap.

    High fiber to resin ratios are best. That's why you'll see vacuum forming when dealing with it. Sucks the form down and squeezes the excess resin out.
    Last edited by Jim Shaper; 07-12-2009, 03:17 PM.


    • #3
      You might look to the Experimental Aircraft Association for information. Quite a bit of home built aircraft projects involve fibreglass and they have a wealth of how to information.

      What used to be in book form now seems to be on DVD. Maybe I just didn't find the right web page but I would prefer a book. Maybe call them and ask.

      EAA Oshkosh WI

      Errol Groff
      EAA 60159
      Errol Groff

      New England Model Engineering Society

      YouTube channel:


      • #4
        It's been a while, but I have done lots of it. There are a few 'tricks' which can make a project sucessful. If a female mold is used, a proper release agent must be used. If a good surface finish is wanted, the mould surface must be properly prepared before the release agent is applied. If you want a finished look right out of the mold, you should use a gel coat of the desired color, and lay up the laminations in the same fashion as you would building a canoe. Look up building fiberglass canoes and there's a lot of info there to guide you, regardless of the type of project that you're doing.

        Corners in molds should be radiused, since figerglass doesn't like being forced into tight corners. It needs to be able to lay against the mold surface without help except for what the surface tension of the resin provides. In all cases, care must be taken that all air is driven out of the layup while the resin is fresh and not beginning to set up. Once setup begins you're pretty much hooped if you haven't rolled the glass out enough to force the air out of the cloth.

        Pay attention to the ratio of calalyst to resin volume, as well as the temperature, and try to avoid working in hot conditions. Catalyzed resin in bulk form will want to set up early by self-heating, so make sure you can use up what you've mixed well before the gel time for the conditions at hand, which basically is temperature and calalyst ratio. If laying up multiple layers of cloth, it's best if you don't wait so long between layers that you have to sand or rough up.

        If you're not using a female mold, but instead laying fiberglass over a framework where it should stick, then pay attention to eliminating sharp corners on that framework, plus make sure that there aren't any glues involved which will interfere with the resin. Ordinary white glue doesn't cut it very well with polyester resin, and if the framework material can absorb moisture it will eventually separate from the fiberglass. If you encapsulate the framework with cloth and resin, make sure moisture doesn't have a way into the framework material.

        If you are facing having to smooth out and finish coat the outside of your layup, then it can be a lot or work to get a nice smooth finish. You can stretch a membrane over the layup to smooth it out, but that's often problematic. You need to have the complete plan in place so you can get the cloth totally impregnated with resin, all the air out, and the membrane pulled down over the layup before the resin begins to set up. You can get good results this way, but you need to know that the membrane can pull down everywhere it needs to before you even begin to try this. Also the membrane has to be immue to the resin. Ordinary poly isn't.

        Regardless of the air temperature, it's best not to work in the sun.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


        • #5
          How To Fiberglass

          There are many tricks for working with fiberglass but you can do many things with out knowing them all. look on you tube for demos!!
          First of all is safty the resins and solvents are all very flammable and the catalyst can explode if it gets to hot one its own. learn hot fast the stuff cooks off, expoy resins have a lot longer working time and is stronger then poly. There are many types of stranded material, some are stronger and thicker then others . Chopped strand mat is easy to use but clothe is stronger and harder to shape.
          Making molds for making multi copies of a part.
          Molds may be male or female (work inside or outside) if you use a female you must be able to get the finish part out. multi-part molds are great when making bigger parts with odd shaped like a car body or fuel tank ect.
          you would use a plug to make a mold the plug is the shape you want the finished part to be like. Special wax is used to help the mold seperate from the plug and the finished parts. gelcoat is use on the finished side of the part for a smooth finish. Tooling gelcoat is used for mold finished surface.
          Gelcoats are better sprayed on, hot pot spraying gelcoat means it has catalyst mixed in and you has a short time to spray. more expensive spraying is the gelcoat and catalyst are mixed external to the gun in the air before landing on the part and have little concern about time to spray.
          I love making things from fibergalss as you can modify a part or make one the did not exsit before you made it. check out my web page to see a 1930 ford woodie I built from scratch the body is fiberglass.

          have fun


          • #6
            Try this sites learning center for some good info on fiber glassing



            • #7
              I blundered my way through one (and my only) fiberglass project, back in the late 70's.
              I had shoehorned a 351 Cleveland engine into my 72 Ford E-300 Supervan.
              The doghouse (engine cover) was too narrow for the new engine, so I used part of the original for a form and used welding rod to make a new curvature for the top. I covered the rod with polyethylene and then covered that with fiberglass. I also sawed the top off and put 1/4 turn clamps on it, to hold the cover on. It was a lot more accessible than the original, since I could remove the top to access the carburetor and air filter. The top did look like a walnut shell, though.
              It is still driving around, now.

              I had very few sources for information at that time and just struggled my way through the project. It cost me $100 for materials but I knew that there was no way I could have one custom built for that price.
              Last edited by ligito; 07-12-2009, 10:05 PM.


              • #8
                An additional advantage of epoxy is that it is MUCH less toxic, non volatile, etc.

                As a basic rule it goes like this: Mix Resin. Cover form w/ Cloth. Apply Resin wettting out the cloth completely. Wipe with Squeegee (not the type for washing windows. Let Dry. Fill Weave before sanding.


                • #9
                  A mixture of different types of Mat and Weave will give you the greatest strength.

                  Start with a tight 2mm Weave, then a heavy couse Mat, then course weave, then tight mat, finished with a tight weave.

                  Use rollers, brushes, squeeges what ever to remove all the air pockets


                  • #10
                    After using various homemade de-airing tools, I found that the ones made specifically for the purpose are actually good for that purpose. Bite the bullet and get a couple, one for corner work and one that's wider, your work will progress faster with less chance of problems.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                    • #11
                      Originally posted by Teenage_Machinist
                      An additional advantage of epoxy is that it is MUCH less toxic, non volatile, etc.

                      As a basic rule it goes like this: Mix Resin. Cover form w/ Cloth. Apply Resin wettting out the cloth completely. Wipe with Squeegee (not the type for washing windows. Let Dry. Fill Weave before sanding.
                      Dont believe epoxy is nice stuff.

                      Epoxy can cause severe allergies, and sensitise you other things.

                      been there done that.

                      every one knows you slather resin and fiberglass on on by the bucket load, and make a heavy lumpy hairy mess , and the grind itchy dust all over the place.

                      Resin infusion.
                      make a mould, in this case a section is good,1/8 or 1/4
                      prep the mould,gel coat it, lay dry fiberglass in mould , put bag over the lot,pull vacuum, inject resin , vacuum pulls resin through glass, let it cure
                      voila, high strength laminate .
                      repeat join sections together.


                      • #12
                        This is gonna be for the dome TMT?? As the basis for a shape don't forget chicken wire, you can pull into some quaint shapes to get a rough outline. Another material to use other than the glass mats and cloths are materials like cottons and man mades as a covering base.

                        Have "Skinned" many model A/C fusegalges with Silk rather than Glasses, in the event of a crash, the molding stays like a bag rather than splits, - makes it easier to pick the bits up. You still have to ensure it's "Wetted" all the way through just like Glass and it works for both Polyesters and Epoxies.

                        Regards Ian.
                        You might not like what I say,but that doesn't mean I'm wrong.


                        • #13
                          Originally posted by Teenage_Machinist
                          An additional advantage of epoxy is that it is MUCH less toxic, non volatile, etc.
                          Really ?

                          Polyester resin is much less toxic, yes it has the high V.O.C. of
                          the styrene thinner in it. But get some on your bare skin, and
                          it isn't nearly the toxicity as epoxy.

                          And as other have mentioned, epoxy (fumes which you really can't
                          smell, but are present in the liquid) can cause "sensitization" in
                          certain people, and when they come into contact (read, walk into
                          the room where epoxy resin was used in the last couple of days)
                          immediately break out in a rash.

                          Flammability is a whole 'nuther issue, it is not related to toxicity.


                          • #14
                            Just my fiberglass experiences

                            I learned about using polyester resin and cloth while a young aspiring surfer, living around Jacksonville beach, Florida. Since the hurricanes of the early 60's washed out about half a block of beach houses, the corps of engineers installed a granite bolder revetment the whole ten mile length of the beaches. This was fine for stopping erosion but it was hell on surfboards at high tide.

                            I learned, the hard way mostly, that resin is a sticky, nasty mess, as was mentioned/ until you learned the handful of tricks of the trade.

                            First, hardening rate of the catalyzed resin is very dependent on the thickness of the section to be laminated. If it is just a gell coat or is a thin coating use plenty of catalyst. The instructions on the can are pretty vague on the ratios so you will have to experiment a little bit.

                            Second, there are two types of resin used and they have a different purpose. Laminating resin is greenish in color and dries to a strong but somewhat flexible and waxy finish. This is what they use when laying up hulls of boats and such. Gell coat is a purplish color and dries smooth, clear, and hard as nails. If you are making something with a thickness of over, say, three eights of an inch, use the green stuff, sand when dry, and top off with a gell coat.

                            Third, sanding fiberglass is very hazardous to your health so use a respirator of decent quality. The secret to sanding down a rough surface and not going broke buying sandpaper is to reduce the speed of the drill or sander to about 10 rpm's and use the coarsest paper you can get. If the paper heats up the dust will melt into the paper making it useless. Finish sand with finer and finer grits at the same low speed until a reasonable surface is achieved. For a final sanding use wet and dry paper with plenty of water in succedingly finer grits down to about 600. You can also create a fine finish without sanding by applying a gel coat and using saran wrap as a squeegee.

                            Fourth, if you are moulding something, I believe the release agent of choice is something called polyvinyl alcohol. Much of this stuff can get found at marinas and boat manufacturers facilities

                            Fifth, if you need to build up a vertical surface, such as the splash well around where an outboard engine goes, you can get "milled glass fiber" to mix into the resin to make a putty consistency that will allow it to stand and not slump.

                            Last of all, when sanding, be sure to wear a long sleeve shirt and hat. That stuff will itch like hell for weeks if you get it on your skin, especially tender spots like the bottoms of your arms, Ask me how I know. You can wind duct tape backwards around your hand and pull some of it out of the skin but not all.

                            I wish I had some links to share but the EAA sites and boat builders sites should tell it good as any.

                            best of luck
                            Jim (KB4IVH)

                            Only fools abuse their tools.