ASTM C1249-18(2023)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1249 − 18 (Reapproved 2023)
Standard Guide for
Secondary Seal for Sealed Insulating Glass Units for
Structural Sealant Glazing Applications
This standard is issued under the fixed designation C1249; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This guide covers design and fabrication considerations
for the edge seal of conventionally sealed insulating glass
2. Referenced Documents
units, herein referred to as IG units. The IG units described are
2.1 ASTM Standards:
used in structural silicone sealant glazing systems, herein
C639 Test Method for Rheological (Flow) Properties of
referred to as SSG systems. SSG systems typically are either
Elastomeric Sealants
two or four sided, glazed with a structural sealant. Other
C679 Test Method for Tack-Free Time of Elastomeric Seal-
conditions such as one, three, five, six sided may be used.
ants
1.2 This guides does not cover the IG units of other than
C717 Terminology of Building Seals and Sealants
conventional edge seal design (Fig. 1); however, the informa-
C794 Test Method for Adhesion-in-Peel of Elastomeric Joint
tion contained herein may be of benefit to the designers of such
Sealants
IG units.
C1087 Test Method for Determining Compatibility of
1.3 In an SSG system, IG units are retained to a metal Liquid-Applied Sealants with Accessories Used in Struc-
framing system by a structural seal (Fig. 2). The size and shape
tural Glazing Systems
of that seal, as well as numerous other SSG system design C1135 Test Method for Determining Tensile Adhesion Prop-
considerations, are not addressed in this guide.
erties of Structural Sealants
C1184 Specification for Structural Silicone Sealants
1.4 The values stated in SI units are to be regarded as the
C1369 Specification for Secondary Edge Sealants for Struc-
standard. The values given in parentheses are for information
turally Glazed Insulating Glass Units
only.
E631 Terminology of Building Constructions
1.5 This standard does not purport to address all of the
E773 Test Method for Accelerated Weathering of Sealed
safety concerns, if any, associated with its use. It is the
Insulating Glass Units (Withdrawn 2010)
responsibility of the user of this standard to establish appro-
E2188 Test Method for Insulating Glass Unit Performance
priate safety, health, and environmental practices and deter-
E2189 Test Method for Testing Resistance to Fogging in
mine the applicability of regulatory limitations prior to use.
Insulating Glass Units
1.6 The committee with jurisdiction for this standard is not
E2190 Specification for Insulating Glass Unit Performance
aware of any comparable standard guides published by other
and Evaluation
organizations.
2.2 IGMA Standards:
1.7 This international standard was developed in accor-
TR-1000-75(91) Voluntary Test Methods for Chemical Ef-
dance with internationally recognized principles on standard-
fects of Glazing Compounds on Elastomeric Edge Seals
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
This guide is under the jurisdiction of ASTM Committee C24 on Building Seals Standards volume information, refer to the standard’s Document Summary page on
and Sealants and is the direct responsibility of Subcommittee C24.10 on the ASTM website.
Specifications, Guides and Practices. The last approved version of this historical standard is referenced on www.ast-
Current edition approved Feb. 1, 2023. Published February 2023. Originally m.org.
approved in 1993. Last previous edition approved in 2018 as C1249 – 18. DOI: Available from Insulating Glass Manufacturers Alliance (IGMA), 1500 Bank
10.1520/C1249-18R23. St., Ottawa, ON K1H 1B8, Canada, https://www.igmaonline.org/.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1249 − 18 (2023)
3.2.5 structural seal—a joint seal of which the sealant
structurally adheres an IG unit to a metal framing system (see
Fig. 2).
3.2.5.1 Discussion—The structural seal transfers applied
loads to the framing system as well as accommodates differ-
ential movements between the IG unit and the framing system.
3.3 Symbols:
2 2
3.3.1 A = area, m (in. ).
3.3.2 C = sealant contact width, shear, mm (in.).
s
3.3.3 C = sealant contact width, tension, mm (in.).
t
3.3.4 D = design factor, dimensionless.
3.3.5 F = allowable shear stress, Pa (psi).
s
3.3.6 F = allowable tensile stress, Pa (psi).
t
FIG. 1 Sealed IG Edge Seal: Basic Components
3.3.7 F = yield stress, Pa (psi).
y
3.3.8 H = height, m (ft).
3.3.9 L = perimeter length, m (ft).
2 2
3.3.10 M = mass per unit area, N/m (lb/ft ).
TM-4000 Insulating Glass Manufacturing Quality Proce-
3.3.11 P = applied load, Pa (lbf/ft ).
dures
3.3.12 W = width, m (ft).
2.3 NFRC Document:
NFRC 706 Requirements for Participating Insulating Glass
4. Significance and Use
Certification Programs
4.1 It should be realized that the design of an IG unit edge
seal for use in SSG systems is a collaborative effort of at least
3. Terminology
the IG unit fabricator, sealant manufacturer, and design
3.1 Definitions:
professional, among others.
3.1.1 Refer to Terminology C717 for definitions of the
4.2 This guide provides information on silicone sealants that
following terms used in this guide: adhesive failure, bead,
are used for the secondary seal of IG units that are glazed into
cohesive failure, compatibility, cure, elongation, gasket,
SSG systems.
glazing, joint, lite, modulus, non-sag sealant, seal, sealant,
sealant backing, setting block, shelf-life, silicone sealant, 4.3 Information is also provided on the other major compo-
nents of the IG unit edge seal, compatibility of components,
spacer, structural sealant, substrate, tooling, and working life.
Refer to Terminology E631 for the definition of sealed insu- durability, and quality assurance (QA).
lating glass as used in this guide.
5. Insulating Glass Unit
3.2 Definitions of Terms Specific to This Standard:
3.2.1 desiccant—a hygroscopic material that adsorbs water
5.1 Insulating Glass Unit Components—The edge seal of an
or may adsorb solvent vapors, or both (see Fig. 1).
SSG system IG unit consists of the two lites of glass, spacer,
3.2.1.1 Discussion—The desiccant maintains a low relative
desiccant, primary sealant, and secondary sealant (Fig. 1) (1).
humidity in sealed insulating glass.
This type of IG unit is referred to commonly as a dual-seal unit
3.2.2 primary seal—A joint seal of which the sealant resists in that it has separate primary and secondary seals. A single-
moisture vapor permeation into the desiccated space of sealed seal IG unit is inappropriate at this time for SSG systems and
insulating glass (see Fig. 1). should not be used. The following sections describe the
3.2.2.1 Discussion—It also resists inert gas permeation (for components of a dual-seal IG unit briefly.
example, argon) from the IG unit sealed space if the intent is to
5.2 Glass and Architectural Coatings:
use an inert gas.
5.2.1 Glass—All types of glass have been used in the
3.2.3 secondary seal—a joint seal of which the sealant
fabrication of IG units, including monolithic, laminated,
structurally unites the two glass lites and spacer of sealed
tempered, heat-strengthened, tinted, heat-absorbing, light
insulating glass (see Fig. 1).
reducing, patterned, and wired. Almost all glass is produced by
the float manufacturing process, in which the glass ribbon that
3.2.4 spacer—a fabricated shape that creates an appropriate
emerges from the furnace is floated on a bath of molten tin,
distance between two lites of glass in sealed insulating glass
allowing gravity to produce essentially flat parallel surfaces.
(see Fig. 1).
5.2.2 Architectural Coatings—These coatings, which are
3.2.4.1 Discussion—As a component of the edge seal
applied to the surface of the glass prior to IG unit fabrication,
system, the spacer also resists vapor migration into sealed
are generally grouped into one of two categories: low-
insulating glass and provides a container for a desiccant.
emissivity or reflective. They are both metallic or metallic
Available from National Fenestration Rating Council (NFRC), 6305 Ivy Ln.,
Suite 140, Greenbelt, MD 20770, https://www.nfrccommunity.org/page/ The boldface numbers in parentheses refer to the list of references at the end of
ProgramDocs. this guide.
C1249 − 18 (2023)
FIG. 2 Typical A-Side SSG System Mullion: Horizontal Section (Vertical Joint)
oxide materials and in some cases are in multi-layers, depos- sealed space of the IG unit. The sealant is designed to fill the
ited onto or into a glass surface. The coatings are deposited space between the sides of the spacer and the faces of the two
primarily by two methods: magnetic sputtering onto the glass glass lites and to develop adequate adhesion to the surfaces of
surface and pyrolitic deposition into the glass surface. Low-
both materials. The primary sealant must also have sufficient
emissivity coatings are visually transparent and reflect long- movement capability to not fail due to limited differential
wave infrared radiation, thereby improving the thermal trans-
movement that may occur between the spacer and the glass
mittance of the glass. In general, they also decrease but to a
lites. Polyisobutylene-based materials have been found to be
lesser extent than reflective coatings, visible light transmission,
very suitable for this purpose. The primary sealant contributes
and transmitted solar radiant energy. Depending on lighting
little to the structural function of transferring lateral loads and
conditions, reflective coatings are generally considerably less
holding the IG unit edge assembly together. These functions
transparent than low-emissivity coatings. These coatings pro-
are fulfilled by the secondary sealant.
vide a reduction in transmitted solar radiant energy, conductive
5.6 Secondary Sealant:
heat energy, and visible light into the building interior. Ceramic
5.6.1 This sealant transfers negative lateral loads, occurring
enamel, silicone, and pressure-sensitive vinyl and polyester
on the exterior lite of glass, to the interior lite of glass, which
film are applied to the surface of glass to make spandrel glass.
then transfers the load to the structural sealant that adheres the
5.3 Spacer—Spacers are fabricated from a variety of mate-
IG unit to the metal framing system. It also functions as the
rials including metals, rigid plastics and foam cured sealant,
adhesive that unites the two glass lites and spacer together as
and combinations of these materials. They are available in
a unit and prevents excessive movement from occurring in the
numerous profiles, depending on the application. Metals typi-
primary seal (2). The secondary sealant must maintain ad-
cally used are aluminum, both mill finish and anodized,
equate adhesion to the glass lites and spacer and also maintain
galvanized steel, and stainless steel. Rigid plastic and foam
other performance properties, such as strength and flexibility
spacers are commonly used with a thin metallic vapor barrier
after prolonged environmental exposure. Failure of the second-
on the backside. Material selection and geometric design can
ary seal to do so could result in excessive movement in the
reduce the heat transfer at the edge of the IG unit. The spacer
primary seal and fogging of the IG unit or adhesive or cohesive
establishes the size of the sealed space, provides surfaces for
failure of the secondary seal and catastrophic failure of the IG
installation of the primary sealant, is a reservoir for desiccant,
unit.
and forms the third surface of the cavity created at the edge of
the glass lites for installation of the secondary sealant. 5.6.2 Four generic classes of sealants are used presently for
a conventional IG unit edge seal system (non-structural seal-
5.4 Desiccant—These substances are hydrophilic crystalline
ant). These sealants are polysulfides, polyurethanes, hot-melt
materials that are installed into the hollow of the spacer,
butyls, and silicones. For SSG systems, only IG units with a
usually on at least two sides of the IG unit. Commonly used
dual-seal (polyisobutylene primary seal and silicone secondary
desiccants are molecular sieves or a blend of silica gel with
seal) have the required durability for the application and are the
molecular sieves. Their purpose is to adsorb residual water and
only sealants permitted for SSG systems.
solvent vapor in the sealed space immediately after fabrication
of the IG units. They also maintain a low relative humidity in
5.7 Enclosed Gas—The IG unit sealed space encloses a gas
the sealed space for the life of the IG unit by absorbing
such as air, argon, krypton, or sulfur hexafloride. Air is
infiltrating moisture vapor.
normally used if conventional thermal resistance properties are
5.5 Primary Sealant—This sealant provides a high level of required. Argon and krypton are used to increase the IG unit
thermal resistance. Sulfur hexafloride is used in applications in
moisture vapor migration resistance and controls and mini-
mizes gas and solvent migration into the IG unit sealed space. which increased resistance to sound transmission is necessary.
The sealant also acts as a barrier to the permeation of inert When using gases other than air, the IG unit edge seal system
gases (for example, argon) when these gases are used in the must be capable of retaining a substantial percent of the gas for
C1249 − 18 (2023)
the life of the IG unit; otherwise, thermal or sound transmission factor (D) of 4.0, and substituting these values into (Eq 1),
performance will decrease to an unacceptable level. results in the following:
5.8 Breather and Capillary Tubes: F 5 559/4.0 5 138 kPa (2)
t
5.8.1 Breather Tube—A breather tube is a small tube or hole
or
that is factory-placed through the spacer of the IG unit to
F 5 80/4.0 5 20 psi (3)
accommodate an increase in sealed air space pressure when an
t
IG unit is shipped to a higher elevation than where fabr
...