b'Application is probably the most important part.FIR 2.1 COEFFICIENT OF THERMAL EXPANSIONThe single most frequent cause of joint failure is in OAK 2.7 OF COMMON BUILDING MATERIALSthe application. Joints that are mis-matched as towidth of substrates, joints that are narrow or thin, PINE 3.0 in./in.- o F x10 -6joints that are deep or at an angle, or joints that are BRICK 3.6three-sided need extra care. The illustrations show GLASS 5.0how basic some of the problems are and how toCONCRETE MASONRY 5.2correct them. It is important to remember that the STEEL 6.5purpose of caulks and sealants is not to substitute MARBLE 7.3for structural joining. No caulk or sealant will "tie" GYPSUM BOARD 9.0two materials together. They will only "seal" the joint COPPER 9.3against air or moisture penetration. ALUMINUM 12.8These guidelines are how to determine the joint size, PVC 40.0but consideration must be given to surface prepara- As the chart shows, this difference in expansion ratetion, adhesion, weather and UV resistance, and caulk must be considered when joining a Vinyl Window toshelf-life. To better explain, look at the diagrams.brick, or pine, or even aluminum, for example. The three main causes of seal failure, regardless of Some basic guidelines to follow:proper width or flexibility are Adhesive Failure, 1. Latex, Acrylic Latex and Urethane AcrylicCohesive Failure, and Substrate Failure. have limited application range and about 25%1. Adhesive Failure is the result of the caulk shrinkage and should not be used during inclementor sealant not sticking adequately to one of the sub- weather or as a back bedding sealant. Excellent forstrates. This will happen if the movement exceedsinterior applications.the sealant\'s capability, if the surface isn\'t prepared 2. Polyurethanes have excellent joint movementproperly, or if the bead isn\'t carefully placed. capability but are prone to UV degradation andbecome less aesthetic over time.BOND BREAKERBOND BREAKER TAPE TAPE 3. Low and medium Modulus Silicones haveexcellent joint movement and UV stability. Tendencyto collect dirt and dust.4. Silyl Modified polymers (MS Polymers) -bestFAILURE O.K. FAILURE O.K. choice as a back-bedding sealant.Compatible withFlashing tape and weather resistive barriers (WRB).BACKER ROD Excellent adhesion to common building materials.5. Elastomeric Polymer have wide temperaturerange application and exhibits approximately 25%FAILURE O.K. shrinkage. Best used as exterior primary sealantFAILURE O.K. where aesthetics are important. HOW TO MAKE BOND BREAKER TAPE A PROPER Which is Best?BOND Best is a relative term. With all the different types of materials that need to be caulked or sealed, it\'s FAILURE O.K. difficult to choose among the variety of brands and2. Cohesive Failure is the result of the types of sealants. To decide which type of caulk orsealant itself failing to hold together. Splits, tears, or sealant will work best, it is better to look first at other ruptures can occur if the sealant dries out, is what caulks are supposed to do, and why mostover-stretched, deteriorates due to time and weather, sealant failures occur.or is improperly mixed or has entrapped air.3. Substrate Failure occurs most often when In simple terms, caulks are supposed to seal a jointthere is inadequate surface preparation. The surface between two materials so that air and moisture that fails probably needed to be sealed, scraped, or cannot penetrate the joint and this joint must stayotherwise prepared to accept the sealant selected. sealed under variable weather conditions and even ifCaulks and sealants fail because they don\'t stick, the two materials move. Therefore, caulks must stickwon\'t move, or they dry out, crack, or shrink.to the two surfaces, have elasticity to withstandThe major considerations are Material Movement movement, and must not deteriorate due to theand Joint Design. The two materials being joinedenvironment. are subject to expansion and contraction due toTo determine which is best for your application,temperature and moisture changes, and there may consider the following:be movement due to use. It is necessary to design a 1. Used inside or outsidejoint that allows the movement without overtaxing 2. Application and Service Temperaturesthe elasticity of the caulk.3. Materials to be joinedWindow Fitters Guide to Window Installation102020 AWDI, LLC Do not reproduce without permission'