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Mat: A random collection ofshort glass fibers held together with a binder. Conforms well to tight curves and also provides asmooth resin rich surface for the outside skin of a molded part. Usuallyavailablein3/4oz and 1.5OZ/ft2 (225 gM/M2 and 450 gM/M2). Cloth:Tightly woven fiberglass that is lightand also drapes well. Often used as the last layer of a laminate. Available inweights from very light1.5oz/yard2 (50 gM/M2) to the more common 6 to 9 o7/yard2 (200 to 300 gM/M2). Woven roving: More loosely woven heavy fiberglass to add strength and thickness to a layup. Core Choices: SAN foam (e.g. Corecell) is most costly but very tough and resistant to impact and easily worked with woodworking tools. PVC foam like Divinycell, Herex and Airexareoften about 20% less costly than Corecelland stilla good choice formost applications. Balsa,thecheapest optionandagood choice where compressivestrength isimportant but isalso the heavi- est option. Where hardware will be through bolted, buildersshould use higherdensity cores. [Ed: D1Y recommends installing hard- ware in cored laminates using the pottingtechnique asoutlinedinD1Y 2005-#2 issue.]Buildersshouldnot usestyrofoamorpolyurethaneinsulation foam becausetheirshearstrengthisnot Vacuum pump equip- ment. Centralto thevacuum bagging process is the vacuum pump. The size of the lami- nate piecesand the amount of mate- rialbeing laid up will determine require- ments.We were able to purchase a 6 CFM, 29" Hg, HVAC tech- nician type used for $150 from eBay. " Airtight mold surfaces need to be built in the shape of the pieces to be made. The mold surface can be Formica, melamine-covered particleboard, glass, smooth metal, etc. We purchased old, discounted sheets of Formica and glued them toa plywood substrate. We also used melamine-covered particle board and found that gave an acceptable surface fin- ish with less expense and preparation. Cost: $22 for a 4' by 8' (1.2m by 2.4m) sheet of melamine-coated particleboard. "We choseflat Corecellfoam core because ourpartswere not curved. You can purchase predrilled core but the cost premium is often enough to make itworth doing yourself. Knifeslitcores, used forcurvedparts, have airpassages that allow air to escape as well and do not require drilling.Cost: 1/2' (12mm) thick Corecell core, 4' by 8' (1.2m by 2.4m) sheet for $125. " Specialty mold release waxes are available from fiberglass supply houses.Carwaxescancontainsilicone,which willcontaminate thesurfaceandhinderfuturepainting.Cost:$18. "Thevacuum bagisthefinallayerinavacuumbaggingopera- tion and forms an airtightseal againstthe mold. We used rolls of4-millightweightplasticsheetingthat areavailablefrom hardware stores. Cost: $10 per roll. "Thebreather/bleederlayerperforms twofunctions:itabsorbs excess resin that bleeds through the peel ply and it also doesn't compress fully so vacuum pressure isdistributed evenlytoallpartsofthepart.Common breather/bleederlayers used arebubblewrap and polyesterbatting quilting material. We used polyester batting because we have seen bubblewrap leaving small dimples in the finished part of other vacuum bagged projects.Cost: $2 peryard. " Peel ply prevents the other layersfrom stickingto the part. We used sale priced Ripstop nylon from a fabricstore. We used many different types and never found any release issues. Commercial peel ply is more costly and isessentially the same material, though itmay be treated to release more readily. Cost: $1 to $2 peryard. " We used stitched triaxial 20 oz (666 gM/M2) E-glassfrom V2 Composites(web: www.v2composites.com), as we were also using itelsewhere on our boat project. However, itonly sells whole rolls so othervendors should be consulted ifyou need smalleramounts. Cost: $8 peryard. "We usedJeffco1310-L6 resinand3155slowhardener.This had a working life of a few hours when mixed in one gallon (3.78L) batches and, with an ambient air temperature in the 60F(15.5C) range.It'sonlyavailablein5gallon(19L)pails so you'll need to contact suppliers for slow or extra slow hard- eners ifusing smaller quantities. Cost: $50 per gallon. Note: Prices in Canadian funds. Divide by 1.10 to convert to U.S. dollars. Lockers underconstruction.(top)The vacuumbaggedpanelshavebeentapedto theexistingcabinstructureandsome fairing compoundhasbeenappliedtotheseam. (bottom) Newlockerpanelsandpartitions fiberglassed in place. ofepoxy thickened with microballons andcolloidalsilica.We usedaplas- ticsqueegee cut into a 112" (12mm) radius as a tool to form the filets into a smooth shape before applying the fiberglass. Once the bottom panel was solidly glassed, we fiberglassed three inter- nal, vertical dividers to the 13' (4m) long locker. This divided up the locker into spaces for the propane tanks, two separate anchor rodes and a fuel tank. The locker top forms the base of new forward seating. N ew fuel tank being installedin locker About the authors: Evan Gatehouse isa navalarchitectandmechanical engineer, with extensive experience in composite boat designandboat mechanical systems.Diane Selkirkisafreelance writerandsailorwith stories and photos published in a variety of magazines. Together they are completing a totalrebuild on "Ceilydh," a Wood'sMeander 40'(12m) catamaran. Stitchedfiberglass fabrics:Available inunidirectional, biaxial,triaxialand quadraxialconstruction.Layersare stitchedtogetherwiththinthreads.Since sufficient. thefabricisnotcrimpedbytheweaving process,the resulting fabric isconsider- ably stronger than plain woven fiberglass types. These fabrics are the best choice forboatswhere weightisimportant. Biaxial weaves are very effective for tap- ing pieces together. Keviar/Aramid: Where impact resistance isimportant,Kevlarisoftenused.This goldencoloredfabricisverystrongbutis dificult to work with. Ittends tofloatin resin due to itslow density, requiresspe- cial scissorsto cutand, when sanded, itforms a fuzzy surface. It is also quite low in compressive strength compared to fiberglass and is expensive. Carbonfiber/graphite: Wherehigh strength and stiffness is important, car- bon fibercan be an excellentchoice. This black colored fabric can be worked similarly to fiberglass. Itsprimary draw- back is high cost but small amounts can be integratedinto a structurewhere strengthismost important. 0-0 Resin Options: Youdon'thavetobeawritertohaveDIY'saudiencereadaboutyourboat.Just sendusacompletedescriptionofyourboat- pointformisokay- alongwith photos.Includedetailsofanyrepairsorupgradesandifavailable,provideabreak- downofmaterials,costsandlabor.Ifpublished,you'llreceiveaDIYHANDS-ON BOATER 1995-2005 CD-ROM (value US$99.95/CDN$119.95). (Seepage64foradditionaldescription.) Emailyourboatinformation andphotostoJanMundyat:tech@&y-boatcom Or Snail Mail to: IntheU.S.:DIYboatowner Magazine,PO. Box1072,Niagara Fals,NY 14304 InCanada: DIYboat owner Magazine,PO.Box 18, Lindsay,ON K9V 4R8 - Ortho/iso polyester resins are the com- monest typeoffiberglass resinavail- able. Offeringlowcost and working ease, these are the best choice where material properties do not have to be high. Vinylester resins are a nice compro- mise betweenthelowcost,lowmate- rialstrengthofortho/iso polyesterres- insand the high cost, high strengthof epoxy resins, They have similar work- ing propertiesto polyesterresins. Epoxies have the highest costs but the best material strength. They are the best choice for bonding to already cured and properly prepped fiberglass partsandarethebestchoicefor vacuum bagging where weight iscriti- cal. Epoxies are much stiffer and have a higher elongation to failure ratio, both qualities that make them a better choice for high strength and stiffness parts. They also offer very long working times. 0- -0 44 D1Y boat owner 2006-2 (www.diy-boat.com) 1-888-658-2628PDF Image | Vacuum Bagging Basics Shop Talk
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