On 20 Jul 2000, Patrick Maun asked about: <<Subject: [Paddlewise] Need Resin Repair Tips Hello all, I am doing some hull repair and touch-ups and would like some tips. First off, I'll be doing a bunch of gel-coat repair on the keel as well as fixing up some scratches.>> <snip> I thought my seminar hand-out might be useful. The actual visual presentation covers a lot more, including "live" demonstrations, Q&A periods, etc. My last seminar was well attended, with one major glitch. The apartment above the Canoe/Kayak Club burst its hot water tank sometime before I arrived early to set up my display. Nobody home. Water gushed from the ceiling everywhere, so by the time I got it all settled down, it was a mad rush to set-up the demo while participants sat patiently waiting through the delay -- kind of rained on my parade, but we did get through it, and I do thrive on pressure it seems. Let me know if you have any suggestions or questions, as I'd like to expand the notes for inclusion on a free website sometime, with pictures. Also, I do a comparison of North American and British lay-ups. It is very dramatic, as I pound a round cut-out vacume-bagged piece as hard as I can with a hammer, with no damage; but, an awl goes through it instantly. On the Brit boat cut-out, nothing penetrates, but it is 40% heavier or so. Lots of interesting info I could share, but too long for PW. As it is, thecore notes below are very long, so delete or scroll down if not interested. Thanks for your time. It may be a few days before I can answer back. ------------------- © Doug Lloyd – Maintenance and Repair of Fiberglass Kayaks Fiberglass Kayak Construction The modern fiberglass kayak employees a number of products in its construction. While epoxy or vinylester resin can provide a superior lay-up if done correctly, the majority of boats are made from a combination of glass fiber reinforcing material and quality, polyester resin. Fiberglass refers to the actual thin fibers or glass filaments, but is also used to describe the reinforcing fabrics made from these fibers and generally, the entire finished product of glass fibers bound in the cured resin. Other non-glass fabrics such as carbon fiber, Kevlar, Dynel and Vectra can also form part of a “fiberglass” lamination. Chemical boatbuilding varies with each manufacturer with respect to the actual material composite (mat, cloth, woven roving, etc), placement and arrangement, thickness, skill and technology of fabrication and assembly methods, and method of lay-up (hand-laid vs. vacuumed bagged). The objective mechanical properties of a fiberglass laminate requiring consideration include tensile, flexural, compression, and impact strength -- which can vary depending upon the type of reinforcing materials used. Other considerations include intended use and market place norms for acceptable strength-to-weight ratios. With only moderate abrasion resistance, cosmetic repairs are inevitable. Understanding Resins Polyester resin is a thermosetting plastic, made from oil products, and cured by chemically applied heat from within the resin during the chemical reaction (exothermic heat) -- ideally hardening at room temperature. This heat is the setting agent that takes molecules in the liquid resin, and cross-links them (polymerization) into a solid plastic (that cannot be re-liquefied). An accelerator (usually cobalt naphthanate) has been formulated into most resins, so only a catalyst is required to start the reaction – usually methyl-ethyl-ketone (MEK) peroxide. Polyester resin eventually cures, even in its airtight container, so ensure you purchase and use new product. A number of different types of resins are commonly available, and this can cause some confusion in choosing a correct product for the intended use. Resins generally fall into two categories: laminating resin and finishing resin. Laminating resin is also known as molding, lay-up, bonding, or unwaxed resin. It is air-inhibited, meaning that it will not cure properly in the presence of oxygen – remaining tacky and difficult to sand as no wax rises to the surface to seal the curing process. The properties of laminating resin allow gel coat to bond to laminations and successive laminations when molding. Finishing resin on the other hand contains a wax additive that will rise to the exposed surface, sealing it to allow complete curing and subsequent sanding. It is nonair-inhibited, and is also called a waxed resin. This waxy surface can prevent subsequent bonding of additional layers, unless well sanded and prepped with acetone. Laminating resin can be converted to finishing resin with the simple addition of a special wax (air-dry) to the laminating resin, or you can attempt to cover the exposed surface with a cellophane type membrane. A general-purpose resin is also available that can be used for either air- or nonair-inhibited requirements, but may not provide optimal performance. Special Resins Polyester resin can be purchased in regular and higher viscosity formulas. Gelled resin is available off the shelf, and would be indicated for use on more vertical surfaces, where avoidance of sagging and running is required. Given the ease, of which a kayak can be positioned, it is unlikely a higher viscosity resin will be needed. Thickening agents such as thixotropic powder can be added to regular resin to create higher viscosities. Gel coat polyester resin is one of the specialty resins that kayak manufactures use to protect the underlying fiberglass structure, provide a reasonably durable wear surface and waterproof barrier, and form vibrant, outside color surfaces. Base formulas are clear to which color pigments are added. Reductions in the use of lead over the last few years has lead to increasing difficulty matching older gel coat finishes, and changed the look of some old favorites. Gel coatings are air-inhibited, so ensure an air-dry agent is added if the gel coat is to be applied topically, unless the supplier has already added the waxed dryer. Gel coat is typically kept from building too thickly in areas where there is greater flexibility. It cures to a brittle finish and can easily crack. Epoxy resin is another thermosetting plastic resin that sets by applied heat, either exothermic or externally, or a combination of the two. Epoxies come in a variety of viscosities, and use between 30% to 50% hardener as part of the added mix to create a reaction (compared to 1% to 2% catalyzed additive with polyester resin). Epoxy resin costs twice as much as polyester resin, but exhibits superior adhesion, greater strength, and bonds to a greater variety of materials. It also shrinks less and offers the ultimate in waterproofness. It is important to use quality brands. Safety and Handling Concerns fall into two main categories: pre- and post-cure handling. Prior to working with cured products, health hazards are very high. The consequences of vapor inhalation range from mild irritation to increasing sensitization – epoxies being the worst. Skin irritation is a real possibility, and dermatitis may occur with skin contact from any resin. Powders and fillers are easily and accidentally breathed in or “puffed” up into one’s face during the mixing phase, so proper precautions must be taken. Strands of fiberglass and milled fibers are at the least, very annoying if they get onto your skin. Fully cured epoxy is physiologically innocuous, but skin contact must be avoided while it is in the viscous and/or gelled state. Liquid chemicals are all too easily splashed about while being mixed and applied. Catalysts, such as MEK, are known to have instantaneous and grave consequences if splashed into your eyes. Working with cured fiberglass still requires caution. Sanding and cutting hardened fiberglass can raise a lot of dust particles, which in reality, are shredded pieces of glass strand. Any use of power sanding equipment demands even more caution. Though chemically inert for the most part, cured fiberglass retains the ability to severely irritate your lungs. The edges of hardened fiberglass can be relatively sharp, as is the edge after cutting. A single strand of fiberglass, coated in cured with transparent resin, can inflict injuries similar to that of a long wooden sliver. The need for protective clothing and safety equipment will depend upon the size of the job, individual sensitivities, and duration of exposure. Clothing that provides as much skin coverage as possible is recommended, both as a layer of defense from minor splashes that could result in a chemical burn, and to keep air-born particles and glass strands away from your skin. Wearing a quality respirator best prevents respiratory irritations and ailments. Disposable dust masks may be adequate for small repair work, but a properly fitted mask is required for power sanding. Wearing an approved respirator with suitable cartridges for the type of chemicals being used is mandatory, especially if working inside a kayak (such as with inside seam work). By working in a well-ventilated area and using common sense, you should be able to avoid dangerous vapors, fumes, and other harmful substances. Always wear eye protection in the form of goggles or a full-face shield, during mixing, poring, or other handling procedures with pre-cured products -- including any and all solvents. Protect your eyes from post-cured particles and dust. Use disposable polyethylene gloves where possible. For back-up protection and even initial protection for small repair work, a barrier hand protectant cream can be applied, allowing easy clean up with soap and water. Use multiple coats, and ensure the barrier cream is intended for fiberglass protection. Avoid using acetone solvents to clean hands and skin, especially with epoxy, which only further dilutes and penetrates more readily into your skin. Common table vinegar is an ideal substitute. Other Rules and Procedures Never smoke or use open flamed heaters in the work area. Keep chemicals away from flame or fire. Keep children and pets out of the work area. Know the emergency steps for chemical burns to skin and eyes and possible ingestion. Read, understand, and follow all directions and precautions recommended by the manufacturer of the product being used. Certain solvents, epoxies, and curing agents are highly flammable and even explosive. Handle these products with care and keep them away from any source of high temperature. Dispose of saturated rags as soon as possible, by burning them away from the work area in an open-air incinerator, or placement in a fireproof metal bucket for future disposal. Store chemicals in a safe, cool, and dry place. Do not store MEK in a metal container as a spontaneous explosion could occur with prolonged reaction. Do not mix products together unless specifically recommended, and in the proportions indicated in the directions. Work in an organized fashion, avoiding haphazard placement of chemical containers near the edge of benches, etc. Ensure adequate lighting is available, but avoid working in direct sunlight if possible. Clean up spills immediately. Do not use sawdust as an absorbent, nor should you dispose resins and hardeners into trash that contains sawdust due to the possibility of spontaneous combustion. Dispose of discarded containers by puncturing a corner of the can and draining the residual out. You can add hardener or resin as appropriate. This will procure an inert mass, which can then be safely discarded once fully cured. Curing resin can get hot enough in the mixing pot to actually ignite surrounding materials if there is enough combustibility. Remove the pot to somewhere safe and well ventilated until the hot gel has fully cured for disposal. Exterior Fiberglass Maintenance In order to get the longest life from your kayak and keep it looking good, some kind of maintenance schedule should be adhered to. Remove stains as they occur. A small amount of acetone rubbed on judiciously with a clean, white rag will remove all but the most stubborn stain. Regular applications of a quality, UV inhibiting wax will help keep the gelcoat from becoming dull and porous. Store your kayak out of the elements if possible, and out of direct sunlight when not in use. Oxidation of the kayak’s exterior surface will inevitably happen over the years, leaving the gelcoat pitted at a microscopic level. Once the process is allowed to go unchecked, rapid chalking will occur and may be irreversible to the point where even wet sanding and cut polish buffing will only temporarily restore luster. Commercial boat yards can gelcoat resurface or paint your kayak, but expect to pay a premium price for this type of full restoration. Gelcoat Scratches Scratches are going to be inevitable, especially along the hull. Some scratches are superficial; others may be more serious. Deeper scratches will require proper repair with new gelcoat or some other filler. For light gelcoat scratches, you can use wet/dry sandpaper. With a good sanding block, start with 320 grit, moving incrementally up to 600 and on to 1200 if you wish. Do not sand in the same direction as the scratch; rather move at an angle in various directions and contain the area of sanding to as small a spot as possible. A power-buffer with polishing compound should restore the gelcoat to almost like new. Be careful not to sand through the gelcoat, or you will be facing a more elaborate repair job. Polishing to factory luster is not always possible. Repairing Damaged Gelcoat Deeper cuts, gelcoat gouges, nicks n’ chips, stress cracks, and opened voids require proper preparation and use of a marine gelcoat filler or equivalent. A second stage cosmetic restoration may also be required. It is best not to let this type of damage go untreated, as water may penetrate into the fiberglass reinforcing below the gelcoat surface. The area to be repaired must be clean and free of debris and anything that might break free, especially around the damaged perimeter. For deep repair work, ensure that any glass fibers protruding above the surface of the gelcoat area are appropriately cut back or sanded off. If a void has opened up somewhere (it will look like an air pocket with an “egg shell” edge), make sure the shinny inside surface is sufficiently roughened up to allow adhesion of a filler. You can use a Dremel tool with a burr-bit to prep gouges, etc, or often times a piece of 120-grit sandpaper can be folded in half on edge, and then the “V” portion used to sand the inside of the longitudinal cavity. The repair area must be thoroughly dry, vacuumed for dust, and wiped down with acetone. . Stress cracks are a little harder to diagnose severity. Surface “spider” patterns indicate either a manufacturing defect (which may only be a cosmetic problem) or an ongoing stress fracture indicating inappropriate flexing. A broken, concentric ring pattern may indicate a one-time impact, which may require fixing if deep enough. Once underlying structural problems have been rectified or a one-time-only-category has been determined, you will need to excavate the crack to the fiberglass below, and then back-fill with filler. Choice of filler is a matter of personal preference, available product, and desired cosmetic outcome. Color-matched pigmented gelcoat is perhaps the easiest product to work with and achieve a good result. Retail kayak outlets should be able to supply you with hopefully, just the right color of gelcoat for the boat you purchased through them. Polyester gelcoat is typically of high viscosity, and normally has had the air-dry agent added by the dealer (double-check). You will need to purchase some MEK catalyst. Do not use old catalyst you may have had around for a while. Remember to treat MEK with extreme caution – wear eye protection. You can add filler if you wish to thicken it up, especially if you need to build up a vertical area such as near the end of the stern keel line. However, the less additives you use, the greater the bond in smaller gouges. You can use a small artist brush or simply a match stick (cut end off first) to drip the mixed gelcoat into the cavities. As gelcoat will shrink, you need to leave it “proud”. Make sure you work the gelcoat in by “tapping” it in place. Use a sectioned cutter blade or razor blade to cut to the level surface, once the gelcoat has hardened a bit, but not before it has fully hardened. It should be like Jell-O when it is ready to “cut”. A second filling is sometimes required. Polish when cured. Alternatively, you can also use epoxy resin -- either “Cold Cure” or the exothermic “West Epoxy” system. Cold Cure will not be compatible with any subsequent gelcoat layers. Thickeners can be added, or even a coloring agent. The match will not be the same as pigmented gelcoat, in most circumstances. Epoxy will yield a longer lasting repair. It is appropriate for larger damaged areas and the deeper gouges, and has less viscosity for filling smaller voids/scratches. MarineTex is a pre-made epoxy filler, that comes in gray or white, and in excellent, but costly. You can also use polyester “Bondo”. It can be purchased in a marine grade, light-grey, with a white paste catalyst. This is a very easy product to use, but being of a putty consistency, it will have to be squeeged into the damaged portion of the gelcoat. Care must be exercised not to leave any on the surrounding, undamaged area (this holds true for any of the thickened resins described above). Regular polyester autobody filler can also be used, but the darker the filler/catalyst, the more the cavity will contrast with the surrounding area. You can gelcoat over any polyester filler, but subsequent scratches show up the least if the filler matches the original gelcoat more closely. As with the gelcoat filler, you can cut back the filler to surface level with a razor blade just prior to the filler hardening. If you wish to sand your choice of filler, rather than cut it back level with a blade, you will need some quality masking tape. The procedure is to apply a suitable length of tape along each side of the gouge, then apply a second strip over each of the first layers. You can then trowel on your filler, level with the top 2 mil layer of tape, then immediately pull off the top layer of masking tape, which will remove the excess filler. Wait until the filler material hardens up a bit, then rough sand the compound level with the remaining tape, being careful not to sand any of the surrounding area and not below the level of the tape. Peel off the remaining tape and let cure for a day. You can then wet sand the repaired area, sanding carefully at an angle to the length of the repair and finishing with polish and wax. Fiberglass Repairs Major damage, such as severe cracks to the reinforcing layers or even punching a hole right through the hull, can be adequately fixed by the do-it-yourselfer. The cosmetic finish may or may not be as adequate. Typically cloth tape is used for repair work of this nature. Much of the success of the repair is determined by good preparation. Inside surfaces must be sanded and cleaned, and outside gelcoat surfaces must be thoroughly sanded with coarse grit paper to allow sufficient adhesion and bonding. It is best to keep the cloth (or mat) from becoming overly saturated with resin, which will produce a brittle repair. A number of layers may be required, with inside and out overlapping -- depending upon the severity of damage and size. You will need to spread the repair out a bit, so as to taper the repair site. Often, the visible outside surface can be sanded flush, then covered with matching gelcoat and buffed out, leaving a relatively unnoticeable repair. Rather than using finishing resin or epoxy resin, you can in the case of hull repairs, use white gelcoat, saturated directly into the fiberglass fabric. Any subsequent gouges would then show up as almost white. If you wish to ensure optimum results, both aesthetically and from the point of safety, it is often best to seek out a professional boat yard for this type of work. Custom Fiberglassing You can create your own additions, alterations, and accessories for you kayak out of fiberglass, including new bulkheads, thigh supports, and even new hatch openings. It is best to make the parts from fiberglass and then use epoxy and cloth tape to “glass” things in place. Epoxy holds better to older fiberglass. Fiberglass bonds to itself well enough, but subsequent items are usually added at the time the kayak is made, while it is still “green”. Epoxy’s tenacious bond is more reliable once the kayak leaves the factory. You will need various supplies depending on what you wish to accomplish. You may need to make a small mold, purchase mold wax and release agents (hair spray works great!). Wax paper is handy for flat or slightly curved surfaces, eliminating the need for special release substances. Minicell foam can be carved to provide a molding form, or you can use quick-setting dental plaster to reproduce items. *************************************************************************** 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/ ***************************************************************************
At 2:13 AM -0700 7/30/00, Doug Lloyd wrote: > >I thought my seminar hand-out might be useful. [BIG SNIP] Thanks for the great document Doug and thanks to everyone else who sent tips. I made my repairs last week and so far they seemed to have turned out well. I lost about a foot and a half strip of gel-coat and punctured the hull a few times a few years back. This is on the stern keel and while most of the repair work I did has been successful, the keel always managed to loose gel-coat after rocky landings etc. I know this is normal wear and tear, but I was sick of having to re-gel coat constantly. So this time, I applied the gel coat, let it lightly set-up, then flushed it with a razor. I let this cure overnight. The next day, I lightly sanded to build up some texture, then put down a foot long strip of fiberglass seam tape. I cut the ends to points and wetted out the glass with polyester resin. I let this cure overnight. I then sanded the strip edges down to flush them with the hull and then went through my normal wet-sanding, first 220, then 400 and finally 600. I then polish the hull with a polishing paste and finally Turtle Wax. The hull looks great. You can see the keel strip if you look (I have an ivory/beige hull) for it. We'll see how it works. I know there may be some delamination due to the wax content in the gel coat, but am thinking that the adhesion may hold. I haven't noticed any change in handling. I keep my boat at a rowing club and they were impressed with the repair, and those guys and gals are pretty fanatical about hull repair. A couple things I have learned over the past couple years doing the occasional hull repair. Not all gel coat resins come with air-inhibiting wax. I get my gel coat resin from Current Designs, and theirs is, but we had some a few years back from, I believe NDK, and theirs wouldn't set up. We later discovered that it contained no wax. Also, when doing the sanding on a hull, use your hands not your eyes to see how things are progressing. Once you quit feeling gel coat edges, you know you're done. I find this a lot easier to do when wet-sanding. Finally, resin and gel-coat will eat through a lot of plastic cups. So if you have to use plastic cups, double or triple them up. My last tip, if you are buying disposable filters for sanding, read the label. Most filters displayed are simply dust filters and the label will explicitly state that they are not for sanding fiberglass. I have only managed to find fiberglass filters from 3M that were quit a bit more expensive than the regular dust filters. If you know you are going to be doing a lot of work, it might make more sense to get a respirator. I got one a few years back and am glad I did, I have a hard enough time keeping latex gloves in stock much less filters. -Patrick *************************************************************************** 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/ ***************************************************************************
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