b'Contractors Guide Quarterly Report: Metallic Coatings for Roofing Panels Metal roofs a having ahaveproventhemselvesover theabrasionresistance to thegalvaremajor impact onthe commercialroofingyears. Aluminum, zinc and blendsnized sheet. The outermost layer is scene; they now are being specifiedofthetwocanprotectsteelandnearly purezinc andisrelatively on projects that just ayears ago,retainlook of arelductile; itn ibutes to the protecfewtheba meta roof.co trlikely wouldincorporated "tra- tion of the galvanizedmaterial by have Galvanizedprovid gr and the in impactesistance Insince the mid 00s, cath protectiontoscruse-17 gal odicatches vanizing ispractice of immers andedgeMoving furtheexposures. ing clean,flat rolled steelther inward toward the base m l, oxide-freeetainto molten zinc to form athecoatingexistsin layersthat coating bondedeasingthat is metallurgically(notbecomeincr ly harduntilit merely laminated) to thesur reach the base steel to which it is steel\'ses face. T process is an economicalelectrochemically fused. T comhishe way toextendtheservicelifeofbination of all these layers to prosteel sheets. T zinc protects theducethegalvan coatingproheized face sur against corrosionby pro vides toughness and resistance to vidingthe steel in twomecha damage in transp , protection tonicalortways - it shields the metal frominstallation and service. the atmosphere, and, most impor The outermost layer of the coattantly,becauseit is moreelec ingformed as aring of pure iscovetronegative than steel,zinc alsozinc that is carried out on the matethe p idescathodic,orsacrificial,rial as it ising withdrawn from the rov beprotection.Ifthecoatingismoltenzincbath. Theu ing nderlybreached and t underlying steelseriesof zinc/ironalloysinthe he exposed, the surrounding zinc goescoating are formed as the result of a intosolution and sacrificesitselfmetallurgicalreactionbetween overthesteel.Evenif areasasmolten zinc and the steelmaterial much as 1 D 4 ch in leng and/orbeing galvanized. As the -in thzinc/iron widthbecomeexposed,thesur a oys form, they will grow pe nll rpending rou zinc will provide cathodicdicular tothesteel surface.The ditional"membraneroofing. Thep to this area aslong aseffect this has on corners and edges rotection life-cyclecostandmaintenancethe coating lasts.of material is that the coating there issueshavemadethesemetallicThe galvanized coating itself isgenerallyis thicker thanthe surroofsa cost-effectivechoiceforconsidereda self-inspectingsys rounding. This is in coating sharp many ofbuilding owners.tem;thereactionbetweenthecontrast to otherprotective today\'stypes of Metalhasitsshare ofdesignmolten zinc andel will notcoatingsthathavea tendency to th steeconcerns, and one that has been ofoccurunless thesteel surfaceisthin out atandof the edgescorners particular concern is metallic corro chemicallyclean.Agalvanizedthe base material. sion. Corrosioncanrangefromcoating that appears to besoundGalvanizedproducts for roofing m r rust marks to complete struc andcontinuousis, in fact,soundapplicatio usuallya G90, ino nsre turalilure.and c tinuous.meaning the coating consists of 0.9 fa onthealnces(both Steel,market leader in met The galvanized zinc coating liter ou of zinc per square foot roofing,has beendesignedwithally becomes part of the steel sub sides). T coating is just under 1 he protectionto withstandthe worststrate - an adhesive bondsev milthick per side and its staying of that Mother Nature can throw at it.eralthousandpsiexists betweenpower dependson the severity of The look and feel of metal doesn\'tthetwo.Becausethe zinc{irontheenvironmentalconditionsit havetobecoveredwithpainttoalloys arerthe underly must endure. The crystal! ization of harde than protect the steel. Metallicingsteel,theyprovideexcellent coatingsContinued on page 8'