ASTM C1249-93(2000)
(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:C1249–93 (Reapproved 2000)
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.Anumber 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-
tioncontainedhereinmaybeofbenefittothedesignersofsuch
IG units.
1.3 In an SSG system, IG units are retained to a metal
FIG. 1 Sealed IG Edge Seal: Basic Components
framingsystembyastructuralseal(Fig.2).Thesizeandshape
of that seal, as well as numerous other SSG system design
C1135 Test Method for Determining Tensile Adhesion
considerations, are not addressed in this guide.
Properties of Structural Sealants
1.4 The values stated in SI units are to be regarded as the
C1184 Specification for Structural Silicone Sealants
standard. The values given in parentheses are for information
E631 Terminology of Building Constructions
only.
E773 Test Method for Seal Durability of Sealed Insulating
1.5 This standard does not purport to address all of the
Glass Units
safety problems, if any, associated with its use. It is the
E774 Specification for Sealed Insulating Glass Units
responsibility of the user of this standard to establish appro-
2.2 Other Standards:
priate safety and health practices and determine the applica-
Sigma 73-8-2B Test Methods for Chemical Effects of
bility of regulatory limitations prior to use.
Glazing Compounds on Elastomeric Edge Seals
2. Referenced Documents
3. Terminology
2.1 ASTM Standards:
3.1 Definitions:
C639 Test Method for Rheological (Flow) Properties of
2 3.1.1 Refer to Terminology C717 for definitions of the
Elastomeric Sealants
following terms used in this guide: adhesive failure, bead,
C679 Test Method for Tack-Free Time of Elastomeric
2 cohesive failure, compatibility, cure, elongation, gasket, glaz-
Sealants
2 ing, joint, lite, modulus, non-sag sealant, seal, sealant, sealant
C717 Terminology of Building Seals and Sealants
backing, setting block, shelf-life, silicone sealant, spacer,
C794 Test Method for Adhesion-in-Peel of Elastomeric
structural sealant, substrate, tooling, and working life. Refer to
Joint Sealants
Terminology E631 for the definition of sealed insulating glass
C1087 Test Method for Determining Compatibility of
as used in this guide.
Liquid-Applied Sealants with Accessories Used in Struc-
2 3.2 Definitions of Terms Specific to This Standard:
tural Glazing Systems
3.2.1 desiccant—a hygroscopic material that adsorbs water
or may adsorb solvent vapors, or both (see Fig. 1).
3.2.1.1 Discussion—The desiccant maintains a low relative
ThisguideisunderthejurisdictionofASTMCommitteeC24onBuildingSeals
humidity in sealed insulating glass.
and Sealants and is the direct responsibility of Subcommittee C24.10 on Specifi-
cations, Guides and Practices.
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 International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1249–93 (2000)
FIG. 2 Typical A-Side SSG System Mullion: Horizontal Section (Vertical Joint)
3.2.2 primary seal—Ajoint seal of which the sealant resists 4.2 Thisguideprovidesinformationonsiliconesealantsthat
moisture vapor permeation into the desiccated space of sealed are used for the secondary seal of IG units that are glazed into
insulating glass (see Fig. 1). SSG systems.
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)fromtheIGunitsealedspaceiftheintentisto 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
insulating glass (see Fig. 1).
5.1 Insulating Glass Unit Components—Theedgesealofan
3.2.4 spacer—a fabricated shape that creates an appropriate
SSG system IG unit consists of the two lites of glass, spacer,
distance between two lites of glass in sealed insulating glass
desiccant, primary sealant, and secondary sealant (Fig. 1) (1).
(see Fig. 1).
ThistypeofIGunitisreferredtocommonlyasadual-sealunit
3.2.4.1 Discussion—As a component of the edge seal sys-
in that it has separate primary and secondary seals. A single-
tem, the spacer also resists vapor migration into sealed insu-
seal IG unit is inappropriate at this time for SSG systems and
lating glass and provides a container for a desiccant.
should not be used. The following sections describe the
3.2.5 structural seal—a joint seal of which the sealant
components of a dual-seal IG unit briefly.
structurally adheres an IG unit to a metal framing system (see
5.2 Glass and Architectural Coatings:
Fig. 2).
5.2.1 Glass—All types of glass have been used in the
3.2.5.1 Discussion—The structural seal transfers applied
fabrication of IG units, including monolithic, laminated, tem-
loads to the framing system as well as accommodates differ-
pered, heat-strengthened, tinted, heat-absorbing, light reduc-
ential movements between the IG unit and the framing system.
ing, patterned, and wired. Almost all glass is produced by the
3.3 Symbols:Symbols:
float manufacturing process, in which the glass ribbon that
2 2
3.3.1 A =area, m (in. ).
emerges from the furnace is floated on a bath of molten tin,
3.3.2 C =sealant contact width, shear, mm (in.).
s allowing gravity to produce essentially flat parallel surfaces.
3.3.3 C =sealant contact width, tension, mm (in.).
5.2.2 Architectural Coatings—These coatings, which are
t
3.3.4 D =design factor, dimensionless.
applied to the surface of the glass prior to IG unit fabrication,
3.3.5 F =allowable shear stress, Pa (psi).
are generally grouped into one of two categories: low-
s
3.3.6 F =allowable tensile stress, Pa (psi).
emissivity or reflective. They are both metallic or metallic
t
3.3.7 F =yield stress, Pa (psi).
oxide materials and in some cases are in multi-layers, depos-
y
3.3.8 H =height, m (ft).
ited onto or into a glass surface. The coatings are deposited
3.3.9 L =perimeter length, m (ft).
primarily by two methods: magnetic sputtering onto the glass
2 2
3.3.10 M =mass per unit area, N/m (lb/ft ).
surface and pyrolitic deposition into the glass surface. Low-
3.3.11 P =applied load, Pa (lbf/ft ).
emissivity coatings are visually transparent and reflect long-
3.3.12 W =width, m (ft).
wave infrared radiation, thereby improving the thermal trans-
mittance of the glass. In general, they also decrease but to a
4. Significance and Use
lesserextentthanreflectivecoatings,visiblelighttransmission,
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
the IG unit fabricator, sealant manufacturer, and design pro-
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
fessional, among others. this guide.
C1249–93 (2000)
and transmitted solar radiant energy. Depending on lighting 5.6.2 Four generic classes of sealants are used presently for
conditions, reflective coatings are generally considerably less a conventional IG unit edge seal system (non-structural seal-
ant). These sealants are polysulfides, polyurethanes, hot-melt
transparent than low-emissivity coatings. These coatings pro-
videareductionintransmittedsolarradiantenergy,conductive butyls, and silicones. For SSG systems, only IG units with a
dual-seal(polyisobutyleneprimarysealandsiliconesecondary
heatenergy,andvisiblelightintothebuildinginterior.Ceramic
seal)havetherequireddurabilityfortheapplicationandarethe
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
5.3 Spacer—Spacers are fabricated primarily from roll-
such as air, argon, krypton, or sulfur hexafloride. Air is
formed hollow metal shapes and are available in numerous
normallyusedifconventionalthermalresistancepropertiesare
profiles, depending on the application. Metals typically used
required. Argon and krypton are used to increase the IG unit
are aluminum, both mill finish and anodized, galvanized steel,
thermal resistance. Sulfur hexafloride is used in applications in
and stainless steel, with aluminum used predominately. The
which increased resistance to sound transmission is necessary.
spacer establishes the size of the sealed space, provides
When using gases other than air, the IG unit edge seal system
surfaces for installation of the primary sealant, is hollow for
mustbecapableofretainingasubstantialpercentofthegasfor
desiccant installation, and forms the third surface of the cavity
thelifeoftheIGunit;otherwise,thermalorsoundtransmission
created at the edge of the glass lites for installation of the
performance will decrease to an unacceptable level.
secondary sealant.
5.8 Breather and Capillary Tubes:
5.4 Desiccant—These substances are hydrophilic crystal-
5.8.1 Breather Tube—Abreathertubeisasmalltubeorhole
line materials that are installed into the hollow of the spacer,
that is factory-placed through the spacer of the IG unit to
usually on at least two sides of the IG unit. Commonly used
accommodate an increase in sealed air space pressure when an
desiccants are molecular sieves or a blend of silica gel with
IG unit is shipped to a higher elevation than where fabricated.
molecularsieves.Theirpurposeistoadsorbresidualwaterand
The breather tube allows the sealed air space pressure to
solvent vapor in the sealed space immediately after fabrication
equalizetotheatmosphericpressureattheinstallationsite.The
of the IG units. They also maintain a low relative humidity in
breather tube is sealed prior to the IG unit installation. Special
the sealed space for the life of the IG unit by absorbing
sealed space gases (see 5.7) cannot be used in IG units that
infiltrating moisture vapor.
have breather tubes.
5.5 Primary Sealant—This sealant provides a high level of 5.8.2 Capillary Tube—A capillary tube is a very thin bore
moisture vapor migration resistance and controls and mini- tube of specific length and inside diameter that is factory-
mizes gas and solvent migration into the IG unit sealed space. placed through the spacer of the IG unit. A capillary tube
The sealant also acts as a barrier to the permeation of inert fulfills the same function as a breather tube and, in addition, is
left open after installation to permit the sealed space of the IG
gases (for example, argon) when these gases are used in the
sealed space of the IG unit. The sealant is designed to fill the unit to continue to pressure equalize with fluctuating ambient
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:
C1184. 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 C1184
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,
afterprolongedenvironmentalexposure.Failureofthesecond-
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
primarysealandfoggingoftheIGunitoradhesiveorcohesive (F ) (or tensile adhesion value) is determined by Test Method
u
failure of the secondary seal and catastrophic failure of the IG
C1135 by pulling to failure small laboratory specimens of
unit. sealant having a cross-section similar (but not necessarily
C1249–93 (2000)
identical) to that used in a structural seal. Sealant manufactur- 6.3.6 It is not within the scope of this guide to specify a
ers usually report this value in a table of performance criteria particular tensile stress (F) for the IG unit secondary sealant.
t
foraparticularsealant.Anexampleofasealantmanufacturer’s
This should be an informed decision made by
...
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