07 92 00: Joint Sealants

by The Adhesive and Sealant Council, Inc. (ASC)

Last updated: 11-01-2007

Introduction

Sealants were used many hundreds of years ago. The Tower of Babel was reportedly built with mortar and tar or pitch as a sealant. Naturally occurring bitumen and asphalt materials have been widely accepted as sealants for many centuries. Prior to the 1900's most sealants evolved from vegetable, animal, or mineral substances. The development of modern polymeric sealants coincided with the development of the polymer industry itself, sometime in the early 1930's.

Joint sealants are used to seal joints and openings (gaps) between two or more substrates, and are a critical component to building design and construction. The main purpose of sealants is to prevent air, water, and other environmental elements from entering or exiting a structure while permitting limited movement of the substrates. Specialty sealants are used in special applications, such as for fire stops, electrical or thermal insulation, and aircraft applications.

Sealants are broadly used in a variety of commercial and residential applications. Common sealants include silicones, acrylics, urethanes, butyls and other polymeric types. Various formulations have been developed over the years, which meet performance specifications as mandated by building codes, as well as per the specific and unique needs of the end user.

Description

Selection of Sealants

The proper application of sealants involves not only choosing the material with the correct physical and chemical properties, but also ensuring one has a good understanding of the joint design, the substrates to be sealed, the performance needed, and the economic costs involved in the installation of the joint sealant.

Typical considerations in selecting a sealant type for the construction industry are:

• Joint Design: The specifics of the joint design and configuration must match up with the sealant's movement capabilities in installed conditions. The practicality of placement and aesthetics also need consideration.
• Physical and Chemical Properties: Mechanical properties of the sealant like Modulus of Elasticity, its stress/strain recovery characteristics, tear strength, and fatigue resistance are all factors that influence the sealant performance in a joint. The polymeric composition along with other additives will affect the regulatory compliance of the product.
• Durability Properties: The adhesion properties of the sealant to the specific substrates, and the aging properties of the cured sealant as they relate to its resistance to ultra-violet radiation, moisture, temperature, cyclic joint movement and bio-degradation can profoundly influence the service life of the installed sealant.
• Application/Installation Properties: Considerations important include the consistency of the sealant, open/tool time, tack free time, application temperature range, and low temperature "gunnability" (i.e. ability to be dispensed easily by sealant gun). Sealants used for interior applications, even in high-rise or light commercial structures, will have properties and needs different from those used in other applications, such as structural glazing or exterior building facades.

Key Features of Sealant Chemistries

Joint sealants come in many different types, and include:

Liquid Applied in the Field

• Latex (water-based, including EVA, acrylic)
  • Used mainly in residential and light commercial construction applications
  • Interior and/or exterior uses
  • Premium products meet ± 25% movement (ASTM C 920, class A)
  • Excellent paintability (with latex paints)
  • Very good exterior durability
  • Exhibit some shrinkage after cure
  • Sometimes referred to as caulk
  • Not used for exterior applications on high rise construction or for applications undergoing significant cyclic movement
• Acrylic (solvent-based)
  • Used in residential and light commercial construction, mainly for exterior applications
  • Generally meet ± 12.5% movement (ASTM C 920, class B)
  • May need special handling for flammability and regulatory compliance
  • Can be painted
  • Short open time; difficult to tool
  • Exhibit some shrinkage upon cure
  • Often used for perimeter sealing; low movement joints
• Butyls (solvent-based)
  • Excellent adhesion to most substrates
  • Limited movement capabilities, generally up to ± 10%
  • Excellent weathering
  • Good use as adhesives in industrial and packaging applications
  • Sometimes used in curtain wall applications where adhesion to rubber compounds is needed
  • Most are stringy and difficult to apply neatly
  • May show some shrinkage after cure; may harden and crack over time on exposed surfaces
• Polysulfides
  • First "high-performance" sealant chemistry; mainly used in industrial applications
  • Poor recovery limits their use in joints with high cyclic movements
  • Can be formulated for excellent chemical resistance (especially for aviation fuel)
  • Good performance in submerged applications
  • Require primer on almost all substrates
• Silicones
  • Structural bonding and stop-less glazing of glass to frames
  • Very good joint movement capabilities; can exceed ± 50% (ASTM C 920, class A)
  • Excellent UV and heat stability
  • Good adhesion to many substrates especially glass; often a primer is recommended on many substrates, particularly porous substrates
  • Not paintable
  • Used in protective glazing systems and to insulate glass to improve thermal performance (reduce heat loss). Also designed for missile impact and bomb blast situations)
  • Acetoxy chemistry based sealants have strong odor, but newer chemistries have very low odor
  • Adhesion is adversely affected by less than perfect application conditions
  • High, medium and low modulus materials available
  • May stain some types of natural stone without primers
• Polyurethanes
  • Used in industrial and commercial applications
  • Excellent movement capabilities, up to ± 50% (ASTM C 920, class A)
  • Not used in structural glazing applications (avoid direct contact to glass)
  • Excellent bonding, generally without a primer for many surfaces
  • Can be formulated for good UV resistance
  • Paintable
  • Some formulations may contain low levels of solvent

Factory Molded

• Gaskets and seals
• Strip-seals
• Compression systems

The following table shows different sealant formulations, rated for selected applications:
(1=no rating, 2=poor, 3=good, 4=excellent)

Use	Latex	Acrylic	Butyl	Polysulfide	Silicone	PU
Submerged	1	4	3	4	1	4
Interior	4	4	3	3	3	4
Exterior	1	2	1	3	4	4
Structural Glazing	1	1	1	1	4	1
Window Perimeter	1	2	1	3	4	4
Expansion Joints	1	1	1	2	4	4
Traffic Joints	1	1	1	3	2	4
Wide Joints	1	1	1	1	2	3
Paintable	4	3	2	1	1	4
Chem. Resistant	1	1	1	4	1	3
EIFS	1	1	1	1	4	4
Tilt-up	1	1	1	2	3	4
Pre-Cast	1	1	1	2	4	4
Cast-In-Place	1	1	1	2	3	4
Brickwork	1	1	1	2	2	4
Curtain Wall	1	1	2	2	4	2
UV Resistance	1	3	2	3	4	3

Application

Joint sealants are used in various architectural applications, which include:

• High-rise and low-rise commercial buildings:
  • Exterior window/perimeters
  • Roofing terminations
  • Expansion joints
  • Interior windows/doors perimeters, baseboards, moldings
• Plaza and parking decks
• Tilt-up concrete exteriors
• Institutional (prisons, schools, hospitals)
• Airport runways and aprons (pavement)
• Bridge and highway joints
• Commercial parking lots and flat work
• Public works (pavement, sidewalks)
• Water and wastewater treatment facilities (including submerged environments)
• Fire-stop material in joints and penetrations
• Structural glazing

Joint Types

• Working Joint (expansion and isolation)—Joints where the shape and size of the sealant joint changes significantly when movement occurs (e.g. control joint, expansion joint, lap joint, butt joint, stack joint)
• Fixed Joint (construction)—Joints that are mechanically fixed to prohibit movement, generally defined as less than 15% of the joint (e.g. air and/or water seals in curtain walls)
• Control—Generally non-moving (but have potential to move)

Common Problems

• Sealants are often the least thought about and contribute the lowest percentage to a project's overall cost; however, they can become the biggest problem if a structure starts to leak.
• There is both science and art to completion of proper joints from design to sealant placement.
• Sealants cannot make up for poor structural or joint design. They need to have:
  • Proper joint design
  • Proper product
  • Proper application

General Joint Design

The following guidelines should be followed in designing and installing sealants properly:

Joint Spacing

• Must allow access for sealing joint and, if necessary, backer rod placement
• Allow sufficient bonding surface to be present
  • Window perimeters
  • Exposed aggregate butt joints
  • Termination details

Design for Sealant Movement Capabilities

• For weatherproofing, minimum depth of 1/4" (6 mm) sealant/substrate bond, and (in most cases) minimum width of 1/4" (6 mm) opening is necessary to ensure that sealant applied from a caulking gun will flow into the sealant joints properly.
• For moving joints, also need to consider:
  • Wider joints (minimum of 1/4" width) as wider joints can accommodate more movement than narrow joints.
  • Use backer rod or bond breaker tape to eliminate a situation of "three-sided adhesion."
  • Use 2:1 width to depth ratio to accommodate more movement than a thick joint (i.e. 1.5:1 or 1:1 ratio). Consider "hourglass" shape.
  • For joint size larger than 1", depth should be kept to about 3/8" to 1/2" (9 mm to 12 mm).
  • The number and spacing of joints is critical to performance.
• Placing the sealant
  • Mix 2-part sealants properly (no entrained air)
  • Tape outside edge of joints if necessary
  • Gun sealant into joint at constant pressure and flow
  • Prevent overlapping sealant (follow SWRI practices)
  • Dry tool sealant to press material against joint walls or bonding surface
  • Check work frequently and keep samples
  • Maintain a job log (e.g. lot no., weather conditions, application procedure)

Materials

• Will the selected material handle the anticipated joint movement requirements?
• Will the sealant adhere to substrate properly—this is probably the most critical element in the selection process?
• Will product endure anticipated weathering exposures?
• Is product compatible with adjacent materials?
• Does the joint size allow for sufficient placement of selected materials?
• Will the product perform under the stated conditions of use?
• Is there history of application success?
• Does the sealant supplier have the necessary in-house resources to support your application in case of problems?
• Do you want to consider third party testing to confirm product performance?

Surface Preparation

• Most common mode of sealant failure is adhesive
• Must remove all weak material on bonding surface of porous substrates
• Surfaces must be clean, dry, free of dew or frost
• Use best practices as recommended by industry experts:
  • Porous: abrasive, high pressure water (allow to dry after), grinding, wire brush
  • Non-porous: 2 rag method

Priming

• Improves the bond in many situations
• Is not substitute for good preparation
• Many products perform w/out primers
• Most commonly used on horizontal and submerged applications
• Must be done properly to work (primers are not error free: may cause "ponding", waiting time, etc.)

Backing materials: Why use backer rod?

• Attain proper wetting of substrate when sealant is tooled
• Control sealant depth
• Prevent 3-sided adhesion
• Recommended Materials
  • Closed cell backer rod: primarily a foam material with a surface skin
  • Open cell backer rod: primarily a foam material without a skin
  • Backing tape: primarily a self-adhesive polyethylene or Teflon material

Not Recommended:

• Any rigid materials
• Silicone sealant as bond-breaker and joint fill

Keys to Success:

• Must be 25% larger than joint width so remains during joint movement
• Don't poke holes in any backing materials, this can cause air bubbles in sealant
• Must be compressed against side walls to prevent leakage through joint and to get proper bond line dimensions
• Function ceases once sealant is applied and tooled

Structural Glazing Applications

Structural glazing involves attaching glass, metal, or other panel materials to a building's metal frame in place of using gaskets and other mechanical attachments. High-performance sealants must be able to withstand wind load and other stresses, and help to transfer these forces to the structure of the building.

For effective structural joint design, the following parameters should be considered:

• "Structural bite"—defined as the minimum contact surface of sealant required on both the panel and frame to account for such environmental factors.
• "Deadload"—the weight that a panel places on a sealant
• "Glueline Thickness"—used to facilitate the installation of a sealant; helps to reduce stress on a structural joint that might result from a differential thermal movement.

Weatherproofing Applications

Weatherproofing helps keep rain and other weather elements from entering a building.

To apply properly, the following parameters must be considered:

• "Joint Movement"—may occur as a result of: changes in temperature, seismic movement, elastic frame shortening, creep, live loads, concrete shrinkage, moisture-induced movements, and design errors.
• "Movement Capability"—The +/- percent value that indicates the amount of movement the sealant can take in "extension (+)" and/or "compression (-)" from its original cured joint width.

Relevant Codes and Standards

Guide Specifications

• Department of Defense:
• UFGS 07 92 00 Joint Sealants
• Department of Veterans Affairs:
• VA 07 92 00 Joint Sealants

Standards and Guidelines

ASTM has developed various standards and guide specifications used in the design, manufacture, testing, and installation of joint sealants. A brief listing of selected application standards follows (For more info, log onto www.astm.org and select "Standards"):

• C1193 Standard Guide for Use of Joint Sealants—This guide describes the use of single- and multi-component, cold-applied joint sealants for parallel joint sealing applications in buildings and related adjacent areas, such as plazas, decks, and pavements for vehicular or pedestrian use, and types of construction other than highways and airfield pavements and bridges.
• C920 Standard Specification for Elastomeric Joint Sealants—This specification covers the properties of a cured single- or multi-component cold-applied elastomeric joint sealant for sealing, caulking, or glazing operations on buildings, plazas, and decks for vehicular or pedestrian use, and types of construction other than highway and airfield pavements and bridges.
• C834 Standard Specification for Latex Sealants—This specification covers one component latex sealants used for sealing joints in building construction.
• C1184 Standard Specification for Structural Silicone Sealants—This specification describes the properties of cold liquid applied, single-component or multi-component, chemically curing elastomeric structural silicone sealants herein referred to as the sealant. These sealants are intended to structurally adhere components of structural sealant glazing systems.
• C1247 Standard Test Method for Durability of Sealants Exposed to Continuous Immersion in Liquids—This test method covers a laboratory procedure that assists in determining the durability of a sealant and its adhesion to a substrate while continuously immersed in a liquid. This test method tests the influence of a liquid on the sealant and its adhesion to a substrate. It does not test the added influence of constant stress from hydrostatic pressure that is often present with sealants used in submerged and below-grade applications, nor does it test the added influence of stress from joint movement while immersed. This test method also does not (in its standard form) test the added influence of acids or caustics or other materials that may be in the liquid, in many applications.
• C1249 Standard Guide for Secondary Seal for Sealed Insulating Glass Units for Structural Sealant Glazing Applications—This guide covers design and fabrication considerations for the edge seal of conventionally sealed insulating glass units, herein referred to as IG units. The IG units described are used in structural silicone sealant glazing systems, herein referred to as SSG systems, SSG systems typically are either two- or four-sided, glazed with a structural sealant. Other conditions such as one-, three-, five-, or six-sided may be used.
• C1299 Standard Guide for Use in Selection of Liquid-Applied Sealants—This guide covers general background information for the comparative evaluation and selection of liquid-applied sealants for use in building construction.
• C1401 Standard Guide for Structural Sealant Glazing—Structural sealant glazing, hereinafter referred to as SSG, is an application where a sealant not only can function as a barrier against the passage of air and water through a building envelope, but also primarily provides structural support and attachment of glazing or other components to a window, curtain wall, or other framing system.
• C1481 Standard Guide for Use of Joint Sealants with Exterior Insulation and Finish Systems (EIFS)—This guide describes the use of single- and multi-component, cold-applied joint sealants, or pre-cured sealant systems for joint sealing applications, or both, in buildings using exterior insulation and finish systems (EIFS) on one or both sides of the joint.
• D5893 Standard Specification for Cold Applied, Single Component, Chemically Curing Silicone Joint Sealant for Portland Cement Concrete Pavements—This specification covers cold applied, single component, chemically curing silicone sealants that are based on polymers of polysiloxane structures and are intended for use in sealing joints and cracks in portland cement concrete highway and airfield pavements. The specification includes both non-sag and self-leveling types of sealants.
• E773 Standard Test Method for Accelerated Weathering of Sealed Insulated Glass Units—This test method covers procedures for testing the performance of preassembled, permanently sealed insulating glass units against accelerated weathering.
• E331 Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference—This test method covers the determination of the resistance of exterior windows, curtain walls, skylights, and doors to water penetration when water is applied to the outdoor face and exposed edges simultaneously with a uniform static air pressure at the outdoor face higher than the pressure at the indoor face.
• E330 Standard Test Method for Structural Performance of Exterior Windows, Curtain Walls, and Doors by Uniform Static Air Pressure Difference—This test method describes the determination of the structural performance of exterior windows, curtain walls, and doors under uniform static air pressure differences, using a test chamber. This test method is applicable to curtain wall assemblies including, but not limited to, metal, glass, masonry, and stone components.

Additional Resources

Trade Associations and Other Organizations

• The Adhesive and Sealant Council
• ASTM International
• Sealant, Waterproofing, & Restoration Institute (SWRI)

Trade Publications

• Adhesives Age Magazine
• Adhesives & Sealants Industry Magazine

ASC Member Joint Sealant Companies

The following companies are members of the Adhesive and Sealant Council and specialize in the manufacture of joint sealants. Boldface type indicates a company that contributed to the development of this work:

• Accumetric LLC
• Concrete Sealants
• Degussa Construction Chemicals Operations/ChemRex
• DAP (Division of RPM)
• Dow Corning Corporation
• Elmer's Products, Inc.
• Foamseal/Novagard Inc.
• Franklin International
• Geocel
• ITW TACC
• Macco Adhesives (Division of ICI Paints)
• Pecora Corporation
• Polymeric Systems
• Sashco Sealants
• Schnee-Morehead, Inc.
• Sika Corporation
• Sovereign/OSI Sealants, Inc.
• The Ruscoe Company
• Tremco Inc. (Division of RPM)