Many sealant problems are associated with installation practice including joint cleaning, primer
application, joint tooling, and material substitution. This section discusses many of these
installation problems, with most of the material based on the article by Warseck in ASTM STP 1069.
Most adhesion problems are caused by a dirty and/or wet substrate when the sealant is applied.
Specifically, this occurs when the substrate is not cleaned at all, a dirty or contaminated solvent is
used, the wrong solvent is used, the rags or brushes are contaminated, and the rag contains lint. In
some cases the envelope design causes the joint to be inaccessible for cleaning. Adhesion
problems can also be associated with the primer application, i.e., no primer, too much primer, the
wrong primer or not allowing the primer to dry before applying the sealant. The weather conditions
during the sealant application are also critical. If it is too cold, the joint is at its widest dimension
and the increased viscosity of the sealant makes it difficult to apply without gaps and difficult to tool.
In warm weather the joint is at its narrowest dimension, and the warm sealant may sag or flow out
of the joint.
Another important installation issue concerns the tooling of the sealant bead. Tooling should
compress the sealant and push it against the backing, assuring good contact with both sides of the
joint, eliminating air pockets and achieving the desired hourglass shape for the bead. If tooling
does not eliminate air pockets, they will expand in hot weather. A bead deformed by improper
tooling may not stretch as easily as desired and may rupture. Or the bead may not have sufficient
bond area to prevent adhesive failure.
Other installation problems can arise from the unauthorized substitution of the specified sealant or
the improper preparation of multi-component sealants. Spillage of one of the components on the
site can often result in incorrect mix ratios. Mixing at too high a speed can result in air being
introduced into the sealant. Also, if too much sealant is mixed at one time, the sealant may begin to
cure before it is applied.