I am getting to the end of my first S & G kit and have a few questions for the construction gods. You know who you are so don't be shy. What determines the weight of fiberglass cloth? Say 4 oz verses 6 oz. Is there a good substitute for wood flour? Why doesn't epoxy bond to older epoxy (say > 3 days old) unless it has been lightly sanded first? Why does slow cure epoxy create a stronger bond than 5 minute epoxy? I am considering either the Pygmy Coho or Arctic Tern as my next kit. It will be a day boat & weekend camping boat. Opinions as to how appropriate these boats are for these activities? Jim et al *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
On 2 Aug 2003 at 22:37, jfarrelly5_at_comcast.net wrote: > What determines the weight of fiberglass cloth? Say 4 oz verses 6 The weight is per square yard. Five square yards of 4 oz will weigh 20 oz. > Why doesn't epoxy bond to older epoxy (say > 3 days old) unless it > has been lightly sanded first? You can bond newer epoxy to previous epoxy if the previous epoxy is not fully cured. The newer epoxy will develop cross-link bonds with the old. If it is fully cured, no cross-links can be formed. In that case, by sanding the surface, you create a larger surface area to bond with - no cross-linking, just surface adhesion. BTW - 3 days sounds too long. With the epoxies I've used, I wouldn't attempt to bond without sanding if it's over 1 day, preferably less.. > Why does slow cure epoxy create a stronger bond than 5 minute > epoxy? It isn't the time, it's the quality of the epoxy. 5 minute is usually cheap stuff. Mike *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
On 2 Aug 2003 at 22:37, jfarrelly5_at_comcast.net wrote: > > > Why doesn't epoxy bond to older epoxy (say > 3 days old) unless it > > has been lightly sanded first? BTW - here's one of the best documents I've found for technical info on epoxies. <http://www.spsystems.com/pdfs/SP%20Guide%20Resin%20Systems.pdf> Mike *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Jim et al wrote: > I am getting to the end of my first S & G kit and > have a few questions for the construction gods. > You know who you are so don't be shy. > I'm probably not one of the construction gods you had in mind, but will take a stab at your questions. > What determines the weight of fiberglass cloth? > Say 4 oz verses 6 oz. > The weight designation is in units of weight per square yard. A heavier cloth may have thicker fibers and/or more fibers per inch in the weave. > Is there a good substitute for wood flour? > Depends on the application. Wood flour produces a very strong putty because the wood absorbs the resin and the wood fibers themselves are mechanically strong. Milled fiberglass will also form a hard putty due to the entanglement of the fibers. Microballoons do not absorb the resin and their spherical shape will not form a three dimensional matrix (but can be faired to a smoother surface in a non-structural application). > Why doesn't epoxy bond to older epoxy > (say > 3 days old) unless it has been lightly > sanded first? > If the epoxy is not yet fully cured, application of the new epoxy resin will allow it to *chemically* bond to the prior application. If the epoxy fully cures, there can be no such chemical bonding between the two applications, and the surface must be roughened to provide microscopic grooves for the new epoxy to *physically* adhere to. Also - as the epoxy cures, an amine 'blush' (non-reacted chemicals from the hardener) can rise to the surface of the epoxy, which can inhibit bonding. As the chemistry of the epoxy differs from different manufacturers, it is best to read the technical literature for the exact product that you are using, and follow the manufacturers instructions rather than relying on general epoxy 'wisdom'. > Why does slow cure epoxy create a stronger > bond than 5 minute epoxy? > I don't think the speed of the cure has anything to do with the functional strength of the bond. The epoxy cure is a non-reversible chemical reaction (a thermoset) that creates new chemical bonds, and the epoxy chemist/formulator can design the epoxy resin to work best for different applications, e.g. boatbuilding vs. recoating bathtubs vs. electrical component manufacture. Not only can the epoxy resin - generally based on bisphenol A - properties be modified, as can the amine hardener properties, other additives - reactive or inert - can be added to the system to optimize the epoxy's use in different applications. Properties that can be influenced by design include but are not limited to: speed of cure, viscosity of the resin prior to cure, wetting ability of the resin, flexibility of the resin after cure, ability of the system to tolerate wider ranges of resin-hardener combinations, electrical properties, etc. On the MAS site, there is a statement that their fastest curing epoxy systems forms the strongest bonds. The five-minute epoxy may be formulated with more reactive sites per unit weight of the resin and a more reactive amine, so such a product may be expected to be more brittle/less flexible than a slower-curing epoxy. The challenge in using a five minute epoxy lies in the fact that it's window of usability is so small. There exists a greater likelihood of not fully wetting out the cloth or having the epoxy start to gel before the user is done applying the epoxy to the site of construction/repair. If this happens, the repair/construction of the item with the five-minute epoxy will not be as 'good' as that made with a slower cure product. In other words - the perception of one product having a stronger bond than another involves many factors besides how fast the resin cures. Good online resources for epoxy information are the web sites of the manufacturers for epoxies typically usedin boat buiding (spend some time browsing): http://www.westsystem.com/ http://www.masepoxies.com/ http://www.systemthree.com/ http://www.raka.com/ SAFETY INFO safety info about the epoxy you are using is a MUST READ, as your health can be impacted. Even though I have been mindful of safety considerations, years of epoxy use have resulted in my being sensitized to the point of having to wear a respirator with organic vapor cartridges when I work with epoxy (else I suffer a tightness in the chest that takes more than a day to go away). http://www.masepoxies.com/safety.htm http://www.westsystem.com/ (link to safety info under green 'Go To' bar on left, or do a search for the term 'MSDS' to see not only the MSDS, but a link to General Safety Guidelines) TECHNICAL AND SAFETY http://www.raka.com/epoxyman.htm FAQ/TECHNICAL INFO http://www.masepoxies.com/mas8.htm http://www.systemthree.com/ (download their epoxy manual) http://www.westsystem.com/ (click on gray "Using West System Epoxy" tab on top) Also check out bulletin boards and newsgroups: http://www.kayakforum.com/cgi-bin/Building/index.cgi rec.boats.building Erik Sprenne *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). 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Re: Jim's epoxy questions: 6 oz cloth is a standard -- representing a compromise between durability and light weight. 4 oz would be OK for deck use, probably, but the hull definitely needs 6 oz cloth ... and a double layer of that in the middle. (Or, triple, if you are making a wood double kayak). Wood flour is light, available, cheap, sands easily, produces a thixotropic mixture with epoxy, and makes fillets that resemble wood. Other fillers can do most of these things, but for a SNG boat, wood flour is first choice as a thickener. "Green" epoxy (no longer liquid, but not fully cured) still has chemically active polymer parts on the surface. If more epoxy is laid on it, good adhesion occurs. Fully cured epoxy has no such molecular-level attachments, so must be roughened for mechanical adhesion as the two layers intercalate. 5-minute epoxy uses a different ingredient (for the hardener?) which makes it weaker ... and much less water-resistant. It has no place in boat building except as a tacking agent to hold parts together for the real epoxy application. -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Thank you. I didn't know this. I used some for a paddle I was going to make out of two pieces of wood glued together to make it thick enough to work with. I didn't end up making the paddle but did cut the glued wood into pieces I used outside. I noticed the pieces had come apart and was surprised. Good thing I didn't make that paddle. I'll stick to the real stuff. Joan > 5-minute epoxy uses a different ingredient (for the hardener?) which makes it > weaker ... and much less water-resistant. It has no place in boat building > except as a tacking agent to hold parts together for the real epoxy > application. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
After using 5 minute epoxy for various around the house projects for over thirty years I can only say that the joint being glued better not be a very important . While it may be convenient it isn't very strong. Brittle is a better description. It certainly makes sense that there would be a difference in quality in epoxies like most other products. Jim et al ----- Original Message ----- From: "Dave Kruger" <kdruger_at_pacifier.com> > 5-minute epoxy uses a different ingredient (for the hardener?) which makes it > weaker ... and much less water-resistant. It has no place in boat building > except as a tacking agent to hold parts together for the real epoxy > application. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Greetings. I'm no expert, but I've built a Chesapeake 17, and I'm presently constructing a Guillemot. I've hung around the bulletin boards a lot, so my ideas may have some validity. (Then again, they may not.) (Guillemont BBS: http://www.kayakforum.com/cgi-bin/Building/index.cgi) (Chesapeake BBS: http://www.clcboats.com/forum/bbs.pl/cart_id=b1d67bd1a598e7163ef0335bd82e7c7 1/) >What determines > the weight of fiberglass cloth? Say 4 oz verses 6 oz. I don't know, but I'll bet that if you posed that question on one of the two forums listed above, you'd get plenty of knowledgable responses. Is there a good > substitute for wood flour? I suppose it depends on what you want it for. I've used wood flour mixed with epoxy to make fillets, for end pours, and to make a rock-hard putty for filling gaps between strips on the Guillemot I'm building. You can use micro balloons to make a putty. My understanding is that the resulting putty is much lighter. I don't know how it compares strength- and hardness-wise. I've also used Cab-o-sil, or silica powder as a thickener for epoxy, when I wanted to use the epoxy as a bonding agent (glue.) Why doesn't epoxy bond to older epoxy (say > 3 > days old) unless it has been lightly sanded first? My understanding is that the new epoxy will chemically bond to the old epoxy if you apply it before the old epoxy has completely cured. If it has cured, then it's too late to form a chemical bond, and you need to create more of a physical bond between the two layers by roughing up the old epoxy. Incidentally, the strip-builders recommend not sanding the wood with finer sandpaper than about 120 grit, to make sure that the resulting roughness is coarse enough for the epoxy to adhere to. I would think the same would apply to a layer of epoxy - I wouldn't fine sand with 600 grit sandpaper if I was just roughing it up for a better bond. Why does slow cure epoxy > create a stronger bond than 5 minute epoxy? Does it? I'm wondering if 5 minute epoxy is actually epoxy, or really polyester resin? Could it be that the resin to hardener ratio is hard to control? Could it be that there isn't time to get it thoroughly mixed when you only have 5 minutes of working time????? > > I am considering either the Pygmy Coho or Arctic Tern as my next kit. It > will be a day boat & weekend camping boat. Opinions as to how appropriate > these boats are for these activities? > No opinion, as I have no experience with these. What kind of boat are you building now? *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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