DESIGN/SEALANTS
3.5 SEALANTS
Sealants are used to prevent the passage of air, moisture (both vapor and liquid), dust and heat
through joints and seams. A variety of different materials are used as sealants including viscous
liquids, mastics, pastes, tapes and gaskets. These materials are used in applications such as panel
joints, expansion and control joints, roofs, and glazing systems. The selection of a particular
sealant is based on the application and the conditions to which it will be subjected in use. The
Sealant, Waterproofing & Restoration Institute (SWRI) guide to sealants is an excellent reference
on joint design, sealant materials, applications and the preparation of specifications. The book on
construction sealants by Panek and Cook is also very good, and is a source of much of the material
in this section. ASTM Committee C-24 on Building Seals and Sealants has developed many
standards on sealants and sponsored two symposia. The proceedings of these symposia are
published in ASTM STP 606 Building Seals and Sealants and ASTM STP 1069 Building Sealants:
Materials. Properties and Performance.
This section is concerned primarily with the elastomeric sealants that are commonly used to prevent
rain penetration and air leakage through joints in exterior claddings. In the face seal approach to
controlling rain penetration, they constitute the primary seal against both rain and air penetration.
While sealant materials and design methodologies exist that provide adequate levels of
performance in these applications, joint sealant problems do exist. Part of the reason for these
problems is that although sealants play a crucial role in building envelope performance and must
function under demanding circumstances, they are only a small portion of the total envelope design
and construction. And because sealants are often perceived as only a minor percentage of the
project, they can be subject to careless specification, inappropriate substitution and poor
application. In addition, joint design and sealant selection can be influenced by aesthetic
considerations to the point where performance problems result.
When sealant joints do fail, the consequences of the resultant air leakage and rain penetration can
be serious. Sealant failures take a variety of forms including the failure of the sealant to adhere to
the substrate (adhesive failure), the tearing apart of the sealant itself (cohesive failure),
discoloration of the sealant or substrate and hardening or cracking of the sealant. Warseck
presents a very thorough discussion of sealant failure, and states that the basic reason for sealant
failure is a lack of attention to detail in the sealant joint design, specification and installation. The
fact of the matter is that sealants are generally installed under a variety of conditions, on many
different substrates, by persons with varying degrees of interest, ability and supervision, and are
subjected to severe deformation and harsh environmental conditions, i.e., temperature, water and
sunlight. Successful sealant joints require a careful design of the joint geometry, the selection of
appropriate and compatible backup and sealant materials, and proper installation practice.
PAGE 3.5-l
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