ASTM C1249-93
(Guide)Standard Guide for Secondary Seal for Sealed Insulating Glass Units for Structural Sealant Glazing Applications
Standard Guide for Secondary Seal for Sealed Insulating Glass Units for Structural Sealant Glazing Applications
SCOPE
1.1 This guide covers design and fabrication considerations for the edge seal of conventionally sealed insulating glass units, herrein 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, six sided may be used.
1.2 This guide does not cover the IG units of other than conventional edge seal design (Fig. 1); however, the information contained herein may be of benefit to the designers of such IG units.
1.3 In an SSG system, IG units are retained to a metal framing system by a structural seal (Fig. 2). The size and shape of that seal, as well as numerous other SSG system design considerations, are not addressed in this guide.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: C 1249 – 93
Standard Guide for
Secondary Seal for Sealed Insulating Glass Units for
Structural Sealant Glazing Applications
This standard is issued under the fixed designation C 1249; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 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, six sided may be used.
1.2 This guides does not cover the IG units of other than
conventional edge seal design (Fig. 1); however, the informa-
tion contained herein may be of benefit to the designers of such
IG units.
1.3 In an SSG system, IG units are retained to a metal
FIG. 1 Sealed IG Edge Seal: Basic Components
framing system by a structural seal (Fig. 2). The size and shape
of that seal, as well as numerous other SSG system design
C 1184 Specification for Structural Silicone Sealants
considerations, are not addressed in this guide.
E 631 Terminology of Building Constructions
1.4 The values stated in SI units are to be regarded as the
E 773 Test Method for Seal Durability of Sealed Insulating
standard. The values given in parentheses are for information
Glass Units
only.
E 774 Specification for Sealed Insulating Glass Units
1.5 This standard does not purport to address all of the
2.2 Other Standards:
safety problems, if any, associated with its use. It is the
Sigma 73-8-2B Test Methods for Chemical Effects of
responsibility of the user of this standard to establish appro-
Glazing Compounds on Elastomeric Edge Seals
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
3. Terminology
3.1 Definitions:
2. Referenced Documents
3.1.1 Refer to Terminology C 717 for definitions of the
2.1 ASTM Standards:
following terms used in this guide: adhesive failure, bead,
C 639 Test Method for Rheological (Flow) Properties of
2 cohesive failure, compatibility, cure, elongation, gasket, glaz-
Elastomeric Sealants
ing, joint, lite, modulus, non-sag sealant, seal, sealant, sealant
C 679 Test Method for Tack-Free Time of Elastomeric
2 backing, setting block, shelf-life, silicone sealant, spacer,
Sealants
2 structural sealant, substrate, tooling, and working life. Refer to
C 717 Terminology of Building Seals and Sealants
Terminology E 631 for the definition of sealed insulating glass
C 794 Test Method for Adhesion-in-Peel of Elastomeric
2 as used in this guide.
Joint Sealants
3.2 Definitions of Terms Specific to This Standard:
C 1087 Test Method for Determining Compatibility of
3.2.1 desiccant—a hygroscopic material that adsorbs water
Liquid-Applied Sealants with Accessories Used in Struc-
2 or may adsorb solvent vapors, or both (see Fig. 1).
tural Glazing Systems
3.2.1.1 Discussion—The desiccant maintains a low relative
C 1135 Test Method for Determining Tensile Adhesion
2 humidity in sealed insulating glass.
Properties of Structural Sealants
3.2.2 primary seal—A joint seal of which the sealant resists
moisture vapor permeation into the desiccated space of sealed
This guide is under the jurisdiction of ASTM Committee C-24 on Building
insulating glass (see Fig. 1).
Seals and Sealants and is the direct responsibility of Subcommittee C24.35 on
Structural Sealants.
Current edition approved Sept. 15, 1993. Published November 1993.
2 3
Annual Book of ASTM Standards, Vol 04.07. Available from SIGMA, 111 E. Wacker Dr., Ste. 600, Chicago, IL 60601.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
C 1249
FIG. 2 Typical A-Side SSG System Mullion: Horizontal Section (Vertical Joint)
3.2.2.1 Discussion—It also resists inert gas permeation (for 4.3 Information is also provided on the other major compo-
example, argon) from the IG unit sealed space if the intent is to nents of the IG unit edge seal, compatibility of components,
use an inert gas. durability, and quality assurance (QA).
3.2.3 secondary seal—a joint seal of which the sealant
5. Insulating Glass Unit
structurally unites the two glass lites and spacer of sealed
5.1 Insulating Glass Unit Components—The edge seal of an
insulating glass (see Fig. 1).
SSG system IG unit consists of the two lites of glass, spacer,
3.2.4 spacer—a fabricated shape that creates an appropriate
desiccant, primary sealant, and secondary sealant (Fig. 1) (1).
distance between two lites of glass in sealed insulating glass
This type of IG unit is referred to commonly as a dual-seal unit
(see Fig. 1).
in that it has separate primary and secondary seals. A single-
3.2.4.1 Discussion—As a component of the edge seal sys-
seal IG unit is inappropriate at this time for SSG systems and
tem, the spacer also resists vapor migration into sealed insu-
should not be used. The following sections describe the
lating glass and provides a container for a desiccant.
components of a dual-seal IG unit briefly.
3.2.5 structural seal—a joint seal of which the sealant
5.2 Glass and Architectural Coatings:
structurally adheres an IG unit to a metal framing system (see
5.2.1 Glass—All types of glass have been used in the
Fig. 2).
fabrication of IG units, including monolithic, laminated, tem-
3.2.5.1 Discussion—The structural seal transfers applied
pered, heat-strengthened, tinted, heat-absorbing, light reduc-
loads to the framing system as well as accommodates differ-
ing, patterned, and wired. Almost all glass is produced by the
ential movements between the IG unit and the framing system.
float manufacturing process, in which the glass ribbon that
3.3 Symbols:Symbols:
2 2
emerges from the furnace is floated on a bath of molten tin,
3.3.1 A 5 area, m (in. ).
allowing gravity to produce essentially flat parallel surfaces.
3.3.2 C 5 sealant contact width, shear, mm (in.).
s
5.2.2 Architectural Coatings—These coatings, which are
3.3.3 C 5 sealant contact width, tension, mm (in.).
t
applied to the surface of the glass prior to IG unit fabrication,
3.3.4 D 5 design factor, dimensionless.
are generally grouped into one of two categories: low-
3.3.5 F 5 allowable shear stress, Pa (psi).
s
emissivity or reflective. They are both metallic or metallic
3.3.6 F 5 allowable tensile stress, Pa (psi).
t
oxide materials and in some cases are in multi-layers, depos-
3.3.7 F 5 yield stress, Pa (psi).
y
ited onto or into a glass surface. The coatings are deposited
3.3.8 H 5 height, m (ft).
primarily by two methods: magnetic sputtering onto the glass
3.3.9 L 5 perimeter length, m (ft).
2 2
surface and pyrolitic deposition into the glass surface. Low-
3.3.10 M 5 mass per unit area, N/m (lb/ft ).
emissivity coatings are visually transparent and reflect long-
3.3.11 P 5 applied load, Pa (lbf/ft ).
wave infrared radiation, thereby improving the thermal trans-
3.3.12 W 5 width, m (ft).
mittance of the glass. In general, they also decrease but to a
4. Significance and Use lesser extent than reflective coatings, visible light transmission,
and transmitted solar radiant energy. Depending on lighting
4.1 It should be realized that the design of an IG unit edge
conditions, reflective coatings are generally considerably less
seal for use in SSG systems is a collaborative effort of at least
transparent than low-emissivity coatings. These coatings pro-
the IG unit fabricator, sealant manufacturer, and design pro-
vide a reduction in transmitted solar radiant energy, conductive
fessional, among others.
4.2 This guide provides information on silicone sealants that
are used for the secondary seal of IG units that are glazed into
The boldface numbers in parentheses refer to the list of references at the end of
SSG systems. this guide.
C 1249
heat energy, and visible light into the building interior. Ceramic seal) have the required durability for the application and are the
enamel, silicone, and pressure-sensitive vinyl and polyester only sealants permitted for SSG systems.
film are applied to the surface of glass to make spandrel glass. 5.7 Enclosed Gas—The IG unit sealed space encloses a gas
such as air, argon, krypton, or sulfur hexafloride. Air is
5.3 Spacer—Spacers are fabricated primarily from roll-
normally used if conventional thermal resistance properties are
formed hollow metal shapes and are available in numerous
required. Argon and krypton are used to increase the IG unit
profiles, depending on the application. Metals typically used
thermal resistance. Sulfur hexafloride is used in applications in
are aluminum, both mill finish and anodized, galvanized steel,
which increased resistance to sound transmission is necessary.
and stainless steel, with aluminum used predominately. The
When using gases other than air, the IG unit edge seal system
spacer establishes the size of the sealed space, provides
must be capable of retaining a substantial percent of the gas for
surfaces for installation of the primary sealant, is hollow for
the life of the IG unit; otherwise, thermal or sound transmission
desiccant installation, and forms the third surface of the cavity
performance will decrease to an unacceptable level.
created at the edge of the glass lites for installation of the
5.8 Breather and Capillary Tubes:
secondary sealant.
5.8.1 Breather Tube—A breather tube is a small tube or hole
5.4 Desiccant—These substances are hydrophilic crystal-
that is factory-placed through the spacer of the IG unit to
line materials that are installed into the hollow of the spacer,
accommodate an increase in sealed air space pressure when an
usually on at least two sides of the IG unit. Commonly used
IG unit is shipped to a higher elevation than where fabricated.
desiccants are molecular sieves or a blend of silica gel with
The breather tube allows the sealed air space pressure to
molecular sieves. Their purpose is to adsorb residual water and
equalize to the atmospheric pressure at the installation site. The
solvent vapor in the sealed space immediately after fabrication
breather tube is sealed prior to the IG unit installation. Special
of the IG units. They also maintain a low relative humidity in
sealed space gases (see 5.7) cannot be used in IG units that
the sealed space for the life of the IG unit by absorbing
have breather tubes.
infiltrating moisture vapor.
5.8.2 Capillary Tube—A capillary tube is a very thin bore
5.5 Primary Sealant—This sealant provides a high level of
tube of specific length and inside diameter that is factory-
moisture vapor migration resistance and controls and mini-
placed through the spacer of the IG unit. A capillary tube
mizes gas and solvent migration into the IG unit sealed space.
fulfills the same function as a breather tube and, in addition, is
The sealant also acts as a barrier to the permeation of inert
left open after installation to permit the sealed space of the IG
gases (for example, argon) when these gases are used in the
unit to continue to pressure equalize with fluctuating ambient
sealed space of the IG unit. The sealant is designed to fill the
air pressure. Special sealed space gases (see 5.7) cannot be
space between the sides of the spacer and the faces of the two
used in IG units that have capillary tubes.
glass lites and to develop adequate adhesion to the surfaces of
both materials. The primary sealant must also have sufficient
SECONDARY SEALANT DESIGN CONSIDERATIONS
movement capability to not fail due to limited differential
movement that may occur between the spacer and the glass
6. Structural Properties
lites. Polyisobutylene-based materials have been found to be
6.1 General:
very suitable for this purpose. The primary sealant contributes
6.1.1 The design of an IG unit edge seal parallels the
little to the structural function of transferring lateral loads and
methodology used for the design of the SSG system structural
holding the IG unit edge assembly together. These functions
joint that adheres an IG unit to a framing system. SSG system
are fulfilled by the secondary sealant.
structural sealants must meet the requirements of Specification
5.6 Secondary Sealant:
C 1184. Presently, there is no comparable specification for
5.6.1 This sealant transfers negative lateral loads, occurring
sealants used for the secondary sealant of IG units; however,
on the exterior lite of glass, to the interior lite of glass, which
sealants should meet the requirements of Specification C 1184
then transfers the load to the structural sealant that adheres the
(as a minimum) in the absence of another applicable specifi-
IG unit to the metal framing system. It also functions as the
cation.
adhesive that unites the two glass lites and spacer together as
6.1.2 The following sections provide the design profes-
a unit and prevents excessive movement from occurring in the
sional with information on the design of the IG unit edge seal
primary seal (2). The secondary sealant must maintain ad-
secondary sealant regarding the following: allowable tensile
equate adhesion to the glass lites and spacer and also maintain
strength; modulus properties; appropriate design factors; and
other performance properties, such as strength and flexibility
design of the secondary sealant for the effects of shear stress,
after prolonged environmental exposure. Failure of the second-
tensile stress, and combined stresses.
ary seal to do so could result in excessive movement in the
6.2 Sealant Yield Stress—The minimum sealant yield stress
primary seal and fogging of the IG unit or adhesive or cohesive
(F ) (or tensile adhesion value) is determined by Test Method
u
failure of the secondary seal and catastrophic failure of the IG
C 1135 by pulling to failure small laboratory specimens of
unit.
sealant having a cross-section similar (but not necessarily
5.6.2 Four generic classes of sealants are used presently for identical) to that used in a structural seal. Sealant manufactur-
a conventional IG unit edge seal system (non-structural seal- ers usually report this value in a table of performance criteria
ant). These sealants are polysulfides, polyurethanes, hot-melt for a particular sealant. An example of a sealant manufacturer’s
butyls, and silicones. For SSG systems, only IG units with a reported value for F would be 896 kPa (130 psi) for a two-part
u
dual-seal (polyisobutylene primary seal and silicone secondary high-modulus seal
...
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