Rex Robertson wrote: > I get good > results on the plastic if I clean it first with acetone then rough it up > with sand paper then use acetone again before applying a couple coats of > contact cement. I let the first coat dry for about 15 minutes then apply > the second, doing the same on the foam or velcro. Did you have trouble with > the velcro trying to curl up after you put the Weldwood contact cement on? > I like the Marine Goop better for velcro because it is thicker. I can apply > one coat and the velcro does not curl up. My Goop tests have resulted in an > excellent bond with foam/fiberglass, foam/foam, velcro/fiberglass, and > velcro/foam but I have not tried it with plastic yet. Someone else on the > list did and had a good result and the instructions say it can be used for > plastic. I sound like a salesman for Goop but have no connection with them, > yet. :) > I think Rex makes a good point, by description of his gluing process, that the preparation of the materials to be glued is a very important part of the gluing process. As far as contact cement use is concerned, gluing velcro or foam (or anything else) to fiberglass should not be as tricky as gluing things to either polyethylene or hypalon. Weldwood Contact Cement (the *Original* formula product - see http://www.dap.com/retail/retail_detail.cfm?catid=4&subcatid=8&prodhdrid=35) is a neoprene-based product and should work well for most fiberglass applications, and maybe for polyethylene and even hypalon if the surfaces are roughed up before gluing. Most adhesives work by either solvating the surface layer of the substrate being glued, and/or by having some type of durable molecule(s) being solvated so that this durable, insoluble part of the adhesive can work its way into microscopic-sized cracks and crevices in the surface of the material being glued. When the solvent evaporates, it leaves the adhesive 'grabbing on' to the microscopic imperfections to provide the adhesive joint. Beyond that, adhesives are either classed as thermoplastic or thermoset, meaning that the glue molecules can be - theoretically - somehow 'loosened' at a later time (thermoplastic), or that the glue has some chemical reaction occuring whereby it forms a *chemically-reacted* three-dimensional (crosslinked) network that cannot be 'loosened' once it has cured (thermoset). One-part adhesives are often thermoplastics (exceptions being those that require atmospheric moisture to cure/crosslink - e.g. silicone and super glue); two part adhesives are typically thermosets. If one is using the adhesive for a structural application (e.g. D-Rings for whitewater open canoe thigh straps), then it's best to follow the exact recommendations of the manufacturer of the widget being glued. OTOH, for non-structural applications (e.g. foam knee/thigh pads, etc.) there is more room for experimentation, as a glue joint failure would not be as critical, and would likely be only an inconvenience until it could be repaired. For both structural and non-structural applications, preparation of the glue joint areas *is* important. IMO, the main thing to look for in a contact cement is that it is waterproof, which should be indicated by it being a solvent-based, rather than a water-based cement. Having said that, I've had good success with the Weldwood original formula product for most boating applications, and I'm now tempted to try it, rather than Aquaseal or a neoprene glue, for neoprene sprayskirt repairs. I did try Weldwood original formula once to repair a hole in a plastic whitewater kayak (glued a milk jug 'patch' over the hole), but it was a temporary fix which eventually came undone due to the flexing of the hull, and I finally had a patch welded over the hole to permanently repair it. My one attempt at using a water-based contact adhesive for knee pads in a FG canoe failed miserably (it peeled away from the FG *and* from part of the foam), and I've sworn off that stuff even though it is more friendly to the environment. A chemist, but not an adhesive chemist, Erik Sprenne *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced/forwarded outside PaddleWise without author's permission Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Sat Aug 19 2000 - 13:14:35 PDT
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