Patching Cowl!
10-11-2004, 05:43 PM
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Patching Cowl!
How about some of your techniques to patch holes in Fiberglass cowlings? I had to remount my cowl after changing engines and now I have 5 holes which are about 3/8" dia. in the cowl where it was previously mounted..I was thinking of laying a thin patch of glass cloth on the back side then filling the holes with body putty or light wood filler then sanding and repainting..or maybe filling sanding smooth and monokote over holes..quicker but probally wouldn't look as good as painted..
10-11-2004, 08:32 PM
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RE: Patching Cowl!
I take a flat piece PETE plastic (polyethyltetraethylene, the clear stuff that a lot of formed packages are made of, has the consistency of windshield material) and wrap it around the outside of the cowl and rubber band it in place, then use fiberglass cloth and epoxy to patch the hole. do it with the area to be patched down on your table and make sure the PETE seals tight at the edges to minimize seepage of the epoxy. use 30 min epoxy if the form of the cowl is compound--I'll explain. 5 min is o.k. if it is a simple curve. Epoxy will not bond to the PETE; when the epoxy hardens, but before full cure, pull the PETE away and you'll have a smooth surface on the outside of the cowl. If it's a compund curve, you can do a little molding from INSIDE the cowl to "bulge" the material to make it follow the curves; don't push too hard, and don't wait too long after the epoxy gets firm. timing is critical. Once you are satisfied of the curve and the epoxy has hardened completely, do another layer inside to thicken and strengthen the patch (if needed). Then sand theoutside, fill any voids with putty and sand til your patch blends with the rest of the cowl. You can recut the hole across your patch edge if you need, because it is essentially the same as the rest of the cowl. One thing: be sure you clean the inside and eliminate ALL residual fuel residue: epoxy will not bond to an oily surface. Sand the inside well and use uncut denatured alcohol to clean the surface. I 've done many repairs this way on fiberglass. Cowls can be tricky because of the compound curves, think your steps through and have every thing you need ready; even with 30 min epoxy you'll have a short window in which to work, once the epoxy begins to cure. I usually keep a sample of the epoxy and test it for stickiness and pliability while the job is setting. if you pull the PETE away before the epoxy has set, it will "stick" and string out. Try the method on a piece of junk first.
For small holes, 1/2 in 0r less, wax paper will work instead of PETE; it will stick a little, but you'll sand the residual off anyway.
For small holes, 1/2 in 0r less, wax paper will work instead of PETE; it will stick a little, but you'll sand the residual off anyway.
