ABSTRACT In The Construction Waterproofing Handbook, in the introduction to his chapter on “Sealants,” William T. Kubal states, “Sealants are not only the most widely used waterproofing materials, but also are the most incorrectly used.” Realizing the critical role sealants provide with all building envelope systems, a design professional must have a clear understanding of the criteria, standard speci¬ fications, terminology, and methods for calculating movement and designing joints. Experience with renovation projects provides the design professional the “firsthand” experience on where, how, and why joints fail. This knowledge not only helps the designer correct the specific renovations project, it also assists in designing new con¬ struction projects. SPEAKER Richard Cook has authored numerous papers on the subjects of roofing, waterproof¬ ing, and building systems. He has presented several papers at national symposia and conferences, including the American Society of Civil Engineers, the Construction Specifications Institute, RQ’s Building Envelope Symposium, RCI’s international conventions, and the Federal Construction Committee in Washington, DC. Mr. Cook has also presented dozens of papers at local and regional meetings and conferences related to waterproofing, and provides building envelope consulting services to the construction industry. CONTACT INFO: rickc@adcengineering.com or 843-566-0161 Cook – 22 Proceedings of the RC1 24th International Convention
INTRODUCTION Consider the following: 1. Wall assemblies, like other components of the build¬ ing envelope, serve three important functions: (1) as part of a structural sys¬ tem, (2) as protection from the weather (heat, cold, rain, etc.), and (3) as the exterior finish or aesthe¬ tics of the building. The “function” of weather¬ proofing is the most prob¬ lematic, and when it fails to perform, it can also affect the structural and aesthetic functions of the wall. 2. It is also not a big secret that wall assemblies leak when three basic condi¬ tions exist simultaneously in a wall assembly: a. Water (most likely rain) is on the wall. b. Openings exist within or between wall assem¬ blies through which the water can pass. c. Forces exist (gravity, surface tension, capil¬ lary action, pressure¬ differential and/or kinetics), that cause the water to enter the openings. 3. The wall assembly of a facility is composed of one or more wall systems, both barrier and redundant [such as backup /rain¬ screen], and a variety of fenestrations, other wall openings, and penetra¬ tions. A critical relation¬ ship exists among these various systems, which comprise the exterior wall of the building envelope. 4. Windows, storefront, and other wall openings are similar to wall systems in that some systems are designed as “barriers” (shedding 100% of the water), while other sys¬ tems incorporate redun¬ dant flashings to provide a secondary drainage mech¬ anism. Depending on the type of wall systems and wall openings, transition or through-wall flashings may be incorporated. In many cases, the common thread that has to “hold” these various systems together is simply the sealant joint. 5. In the introduction of his chapter on Sealants, William T. Kubal, in his book, The Construction Waterproofing Handbook, states, “Sealants are not only the most widely used waterproofing materials, but also are the most incorrectly used” (and, I would add, most over¬ looked in construction documents) . Realizing the critical role sealants provide with all building envelope systems, a design pro¬ fessional must have a clear un¬ derstanding of the criteria, stan¬ dard specifications, terminology, and methods for calculating movement and designing joints. Experience with renovation pro¬ jects provides the design profes¬ sional the firsthand experience on where, how, and why joints fail. This knowledge not only helps the designer correct the failures of the specific renovation project, but it also provides valuable insight to be used when designing new con¬ struction projects. CRITERIA ASTM International provides a series of documents that contain valuable information on the sub¬ ject of sealants. We commonly see these standards referenced in industry guides, specifications, and manufacturers’ literature, but do we know what information they contain and how to use these standards? ASTM Cl 193 – 05a Standard Guide for Use of Joint Sealants As noted within the scope of this standard, the guide describes the use of a cold, liquid-applied sealant for joint sealing applica¬ tions. Including joints on build¬ ings and related adjacent areas such as plazas, decks, and pave¬ ments for vehicular or pedestrian use, it also addresses issues such as substrate, cleaner, primer, sealant backing, bond breaker, liquid-applied sealant, procured sealant, and in situ test methods as well as types of construction other than highways and airfield pavements and bridges. This guide primarily addresses singleand multicomponent sealants, but also, secondarily, precured sealants. A sealant within ASTM Cl 193 must meet ASTM C834, Spe¬ cification for Latex Sealants; C920, Specification for Elasto¬ meric Joint Sealants; or C1311, Specification for Solvent Release Sealants. As stated in the guide, Proceedings of the RCI 24th International Convention Cook – 23 This guide does not pro¬ vide information or guide¬ lines for the use of a sealant in a structural sealant glazing applica¬ tion. Guide Cl 401 should be consulted for this information. Additionally, it also does not provide information or guidelines for the use of a sealant in an insulating glass-unit edge seal used in a struc¬ tural sealant-glazing ap¬ plication. Guide Cl 249 should be consulted for this information. Practice C919 should be consulted for information and guidelines for the use of a sealant in an applica¬ tion where an acoustic joint seal is required. Guide Cl 299 should be consulted for information on … [characteristics and] properties, such as hardness, tack-free time, or curing process, among others. I. Substrate: Sealants are used to seal joints between various sub¬ strates. The type of substrates are categorized as follows: 1. Porous Substrates – brick, masonry, concrete mason¬ ry, concrete, unpainted wood, some building stones, and most cement¬ based materials. 2. Nonporous Substrates – stainless steel, lead-coated copper, anodized alumi¬ num, factory-applied organic coatings, paints, and glass. 3. EIFS (Exterior Insulation and Finish System) – a porous substrate. Most manufacturers recom¬ mend adhering the seal¬ ant to a base coat and avoiding adhesion to the top coat, which can be softer. II. Cleaner: The cleaning methods and cleaning solutions used are important to the quality of the sealant. Procedures are typically differentiated between porous and nonporous substrates. 1. Porous Substrate – Dust, dirt, contaminants, lai¬ tance, or substances from the preparation process are ground, brushed, blown off with oil-free compressed air, and wiped with cloth. 2. Nonporous Substrate – degreasing solvents, such as MEK, toluene, xylene, acetone, and mineral spir¬ its have been used as cleaners. To ensure no residue film exists on cleaned surfaces, a solu¬ tion of 50/50 IPA (alcohol) and water is often recom¬ mended; thus, a two-step process may be necessary. III. Primer: The purpose of a primer is to improve the adhesion of a sealant to a substrate. 1. A primer changes chemical characteristics of a sub¬ strate. 2. It stabilizes the substrate surface (fills pores and strengthens weak areas). 3. It reduces capillary pres¬ sure of moisture through the substrate surface. 4. Primers may or may not be required on porous and nonporous surfaces. If the need for priming is in doubt, adhesion testing with and without a primer is recommended. IV. Sealant backing: Sealant backing is critical to the perfor¬ mance of sealant. Sealant backing should meet the requirements of C1330, Standard Specification for Cylindrical Sealant Backing for Use with Cold, Liquid-Applied Sealants. Commonly used materi¬ als include polyurethane, polyeth¬ ylene, and polyolefin foams. 1. Function: Sealant backing (or backer rod) serves the following functions: a. Controls depth and shape of sealant. b. Assists in attaining full “wetting” to the sides of the joint when the sealant is tooled. c. Allows movement of the backside of the sealant between substrates. d. Sometimes, it is claimed to serve as a temporary seal, sec¬ ondary barrier, or both. Caution is needed in regards to this claim. 2. Types: The common types of sealant backing (backer rod) include: a. Open-cell foam: • Normally polyure¬ thane. • Does not have sur¬ face skin. • Cylindrical, rectan¬ gular, or other shape. • Low density and easily compressible. • Assists in air or moisture cure process of sealant. • Can wick and retain moisture. • Typically 50% wider than the actual joint width. b. Closed-cell foam: • Typically made from polyethylene, but neoprene, butyl, EPDM, or combina¬ tions also exist. • Low density and less compressible. Cook – 24 Proceedings of the RCI 24th International Convention • Does not tend to wick or retain moisture. • Typically 25-35% wider than the actual joint width. c. Bicellular foam: • Typically made from polyethylene material extruded into cylin¬ drical shapes that have a surface skin. • Cut ends can wick and retain water. • Skin can pose appli¬ cation problems. d. Others: • Some joint applica¬ tions may require use of an elastomeric material such as butyl, EPDM, neo¬ prene, or other back¬ ing material. • They can be form¬ ulated as closed-cell, sponge, or dense rub¬ ber gasket, which can be used as a sealant backing but may require a bond¬ breaker tape. 3. Shapes: Commonly, shapes include round, rectilinear (for standard joints), and triangular (for fillet joints). 4. Applications: Are defined in two categories – vertical and horizontal – which may affect the type of materials used. a. Vertically oriented sur¬ faces • Sloped 15° or more. • Open, closed, or bicel¬ lular. • Water absorption may be deciding factor. b. Horizontal surfaces • Generally extruded, closed cell. 5. Joint filler: Commonly encountered in masonry or concrete construction to form an expansion or iso¬ lation joint for the remain¬ ing joint depth. a. Compressible, asphaltimpregnated cane fiber for concrete substrates. b. Closed-cell polyethylene for masonry substrates. V. Bond breaker: Used to prevent adhesion of a sealant to any sur¬ face or material on which adhe¬ sion would be detrimental. A bond breaker is usually a self-adhesive, pressure-sensitive tape made from TFE fluorocarbon or polyeth¬ ylene to which a sealant will gen¬ erally not adhere. • Duct tape is unacceptable. • Liquid-applied bond breaker is not recom¬ mended due to application issues. • A bond breaker is not re¬ quired with soft, flexible, open-cell-sealant backing material, in that these materials would not signif¬ icantly restrict movement. • Compatibility and adhe¬ sion testing recommended. VI. Liquid-applied sealant: Common types include singleand multicomponent (sometimes noted as two components). 1. Single component (mois¬ ture-cured) Typically defined by the fol¬ lowing: • Requires no mixing. • Ready for application. • Atmospheric moisturecured and thus, slower cure time. • Formulated for slower cure time for extended shelf life. • Not recommended for arid or desert regions. 2. Multicomponent (chemicalcured) Typically defined by the fol¬ lowing: • Mixed at site just prior to application. • Typically two compo¬ nents, but sometimes three. • Rapid cure after mixing. • Thorough and proper mixing is critical. VII. The modulus is typically defined by the following: 1. Stress at a corresponding strain (elongation). 2. Expressed as a percent of the original at-rest dimen¬ sion. a. Low modulus: • High movement capability. • When extended, cre¬ ates a relatively low stress at the sealant and substrate inter¬ face (good for EIFS). b. Medium modulus: • Used for generalpurpose joint sealant applications. • Represents the majority of the products in the industry. c. High modulus: • Normally not used for joints that expe¬ rience movement. • Common for glazing sealant wherein glass or other pan¬ els are sealed to framing system (that exhibits no or very low move¬ ment). Proceedings of the RCI 24th International Convention Cook – 25 ASTM C920-05 Standard Specification for Elastomeric Joint Sealants. This is the most widely recog¬ nized ASTM standard for sealants in that it is referenced throughout the majority of guide specifica¬ tions and manufacturers’ litera¬ ture. This standard specification for elastomeric joint sealants covers “the properties of a cured singleor multicomponent, cold-applied elastomeric joint sealant for seal¬ ing, caulking, or glazing opera¬ tions on buildings, plazas, and decks for vehicular or pedestrian use, and types of construction other than highway and airfield pavements, and bridges.” This standard defines types, classes, grades and uses. Classification of sealant by type, grade, class and use. 1. Types are labeled “S” for single component (typically moisture-cured) and labeled “M” for multicom¬ ponent (typically chemicalcured). 2. Grades are differentiated by the designation of “P” for pourable or self-level¬ ing for horizontal joints under specific conditions, and “NS” for nonsag or gunnable for vertical joints. 3. Classes are defined based on their abilities to with¬ stand an increase of a minimum percentage and a decrease of a minimum percentage of the joint width measure at the time of application and meeting all other requirements of this specification (i.e., Class 100/50, Class 50, Class 35, Class 25, and Class 12.5). 4. This last classification indicates the intended use for the sealant: • T – for use in pedestrian and vehicular traffic areas. • NT – for use in non¬ traffic areas. • I – for use when contin¬ uously submerged in a liquid (if Class I and II exist) . • M – for use with mortar specimens based on required testing within this standard. • G – for use with glass specimens based on required testing within this standard. • A – for use with alu¬ minum based on required testing within this standard. • O – for use on substrate other than the standard substrate based on re¬ quired testing within this standard. This standard also addresses general requirements such as sta¬ bility, color, and issues of surface condition and primers. ASTM C717-06a Standard Terminology of Building Seals and Sealants With inconsistencies in termi¬ nology in the industry, ASTM C717-06a, Terminology of Build¬ ing Seals and Sealants, covers “the terms, related standard defi¬ nitions, and descriptions of terms used or likely to be used.” Definitions for commonly mis¬ understood or misused terms can be found within this document. Examples from ASTM C717 include: Adhesive failure (n): in build¬ ing construction, failure of the bond between the sealant, adhesive, or coating and the substrate surface. Caulk (v): in building con¬ struction, to install or apply a sealant across or into a joint, crack, or crevice. Caulk (n): See sealant. In building construction, a material that has the adhe¬ sive and cohesive property to form a seal. Caulking (n): See sealant. In building construction, a material that has the adhe¬ sive and cohesive property to form a seal. Caulking compound (n): See sealant. In building construc¬ tion, a material that has the adhesive and cohesive proper¬ ty to form a seal. Elastomeric (adj): having the characteristics of an elas¬ tomer. Elastomer (n): a macromolec¬ ular material that returns rapidly to its approximate original dimensions and shape after substantial defor¬ mation by a weak force and release of the force. ASTM C1472-06, Standard Guide for Calculating Move¬ ment and Other Effects When Establishing Sealant Joint Width The standard guide for calcu¬ lating movement is C1472-06, Standard Guide for Calculating Movement and Other Effects When Establishing Sealant Joint Width. This document “provides information on performance fac¬ tors such as movement, construc¬ tion tolerances, and other effects that should be accounted for to properly establish sealant joint size. It also provides procedures to assist in calculating and deter¬ mining the required width of a sealant joint, enabling it to respond properly to those move¬ ments and effects. Information in this guide is primarily applicable to single- and multicomponent, cold-applied joint sealants and secondarily to precured sealant extrusions when used with prop¬ erly prepared joint openings and substrate surfaces.” Cook – 26 Proceedings of the RCl 24th International Convention Figure 1 – Cohesive failure. Photo 1 – Cohesive failure. Designers must consider ther¬ mal movements (coefficient of lin¬ ear expansion), moisture move¬ ments (such as in a masonry walls), shrinkage/ creep (as in con¬ crete walls), and load-imposed move¬ ments (such as seismic and wind). LESSONS LEARNED With renovation projects, we have the opportunity to see first¬ hand where, how, and when joints succeed and when and why they fail. Thus, instead of just adhering to general criteria and guidelines and calculating “anticipated” movements, we can actually view how the joints performed under specific conditions. Photo 2 – Adhesive failure. Figure 2 – Adhesive failure. Proceedings of the RCI 24th International Convention Cook – 27 Photo 3 (left) and Figure 3 – Compression failure. By understanding how seal¬ ants fail in the field, we can adjust the design and/or materials to address the sealant joint needs on existing facilities and apply this knowledge when working on new construction projects. 1. Cohesive failure a. A failure of the sealant characterized by a rupture or separation within itself when subjected to external forces. b. Commonly due to a lack of or improper joint design in the contract documents, improper / insufficient sealant materials, or improper depth-to-width ratios during application. 2. Adhesive failure a. A lack of or a failure of the bond between the sealant and the substrate sur¬ faces. b. Commonly due to a lack of or improper tooling, in¬ compatible materials, con¬ taminants on the sub¬ strates, or lack of primer on substrate. 3. Compression failure a. A failure of the sealant due to the substrate compress¬ ing the sealant out of the joint due to improper joint design. b. Commonly due to improp¬ erjoint design or failure to anticipate wall material movements. 4. Untooled joints a. An insufficient tooling or lack of tooling of the TOOLED JOINT FULL ADHESION Photo 4 – Untooled joint. Figure 4 – Sealant tooling. Cook – 28 Proceedings of the RCI 24th International Convention be caused by extreme cold, internal stresses, or lack of elasticity under external forces of weathering. b. Chalking of the sealant is also evident in some instances. c. A false crazing can also occur when a nonflexible paint is applied over a sealant joint. Due to the joint movement and the inflexible paint, a crazing of the paint occurs. 7. Reversion a. The depolymerization of a high-performance sealant causing the cured elas¬ tomeric network to return to its original mastic state. This is caused by UV degradation, moisture, or a combination of both. b. Sagging has a similar appearance, but is a sealant joint can substantially affect the level of adhesion to the substrates (adhesive failure) and the water resistance of the joint. b. Due to improper applica¬ tion. 5. Compressed or braided backer rod a. A backer rod is oversized so that the backup material is between 25- 50% compression, based on type of material. b. Undersized backer rod will not limit the depth of the cavity during sealant application. c. Oversized backer rod or twisted/ braided backer rod creates creases or crevasses within the backer material. These can cause failures within the sealant joint. 6. Craze cracks (crazing or alli¬ gatoring) a. A maze or random pattern of fine cracks in the sealant surface that can Figure and Photo 6 – Crazing (chalking) and alligatoring. flow of uncured sealant within the joint resulting in Proceedings of the RCI 24th International Convention Cook – 29 Photo 7 – Reversion. Figure 7 – Reversion or sagging. the loss of the sealant’s original shape. 8. Window gasket repair (wet seal/cap bead) a. Window and curtain wall systems include gaskets made of various materials (vinyl, neoprene, etc.). b. Examples of an interim repair to failed gaskets include partial or complete Figure 8A – Cap bead- Figure 8B – Wet seal. removal of the failed, dis¬ engaged, or shrunken gas¬ ket. c. An interim repair requiring removal of the gasket and a backer rod and cap bead installed or the upper lip cut off and a wet seal applied. Incompatibility of the existing material with new sealants can be an issue. d. Removal of the gaskets in whole or in part can affect the window system’s resis¬ tance to wind forces. 9. Redundant sealant system Although many sealant sys¬ tems act as a barrier with no redundancy, redundancy can pro¬ vide a cost-effective option to own¬ ers in many cases. A method used to provide redundancy (a sec¬ ondary drainage path with a sealant joint) is the “double” sealant joint system. It is com¬ monly used with concrete tilt-up panels. In theory, these monolith- Photo 8A – Window gasket. Cook – 30 Proceedings of the RCI 24th International Convention Photo 8B – Window gasket. joints from the exterior environ¬ ment – a key contributor to seal¬ ant deterioration, weathering, and failure. The redundant joint can also be an effective method to address wall systems (such as exposed aggregate and split-faced block) in which it is more difficult to attain a quality application due to surface irregularities and varia¬ tions. ic panels do not allow water pene¬ tration through the panels, but potential deficiencies (cracks, etc.) panel termination, and the move¬ ments that occur at these loca¬ tions justify the redundancy. This exterior sealant joint redundancy also “protects” the inner sealant CONCLUSION Construction remains imper¬ fect, as does manufacturing and designing; but a better under¬ standing of criteria, standard specifications, terminology, and materials will always improve the process from manufacturing through to design, construction, and maintenance. Understanding how sealants fail further clarifies our understanding, allowing us to improve the “common denomina¬ tor” of the numerous wall assem¬ blies for renovation projects and new construction. REFERENCES 1. SWRI (Sealant, Water¬ proofing, and Restoration Institute) has made signif¬ icant strides in improving the manufacturing process through validation of materials. • SWRI’s Sealant Valida¬ tion Program esta¬ blished three priority performance character- Photo 9 – Double joint detail. Proceedings of the RCl 24th International Convention Cook – 31 istics and their respec¬ tive ASTM standards. They have documented construction considerations through their manuals, such as: • Sealants: The Profes¬ sional’s Guide, SWRI, 1995. 2. RCI, Inc. is making com¬ parable strides within the education of the design professional. The associa¬ tion for roofing, water proofing, and exterior walls has developed two 2- day courses for Advanced Waterproofing and for Exterior Walls and has corresponding registration programs. 3. ASTM International • ASTM Cl 193-05a, Standard Guide for Use of Joint Sealants • ASTM C834-05, Specification for Latex Sealants • ASTM C13 11-02, Specification for Solvent Release Sealants » ASTM C 920-05, Standard Specification for Elastomeric Joint Sealants • ASTM C1401-02, Standard Guide for Structural Sealant Glazing • ASTM C1249-06a, Standard Guide for Secondary Seal for Sealed Insulating Glass Units for Structural Sealant Glazing Appli¬ cations • ASTM C9 19-02, Stan¬ dard Practice for Use of Sealants in Acoustical Applications • ASTM C1299-03, Standard Guide for Use in Selection of Liquid- Applied Sealants • ASTM C1382-05, Test Method for Determining Tensile Adhesion Properties of Sealants When Used in Exterior Insulation and Finish Systems (EIFS) Joints • ASTM C1328-05, Standard Specification for Plastic [Stucco] Cement • ASTM Cl 330-02, Standard Specification for Cylindrical Sealant Backing for Use with Cold Liquid Applied Sealants • ASTM C717-06a, Terminology of Building Seals and Sealants • ASTM C1472-06, Standard Guide for Calculating Movement and Other Effects When Establishing Sealant Joint Width 4. Julian R. Panek and John Philip Cook, Construction Sealants and Adhesives, 3rd Edition, 2004. 5. Michale T. Kubal, Con¬ struction Waterproofing Handbook, McGraw-Hill, Inc., 2000. 6. Joseph Amstock, Hand¬ book of Adhesives and Sealants in Construction, 2000. 7. Water in Exterior Building Walls: Problems and Solutions, Thomas A. Schwartz, editor, ASTM STP 1107, February 1992. Cook – 32 Proceedings of the RCI 24th International Convention
