Technical Details: Sealing the Deal
Not all building leaks occur at the roof. After a new roof is installed, additional leaks can still occur if the joints at exterior components at the roof level are not properly sealed. A best design practice is too include proper sealant application requirements in the remedial roof design.
Sealants are applied at a number of points throughout a roof application. They are applied at counter flashing joints, metal seams, at tubular penetration flanges, and a plethora of openings in the roof system or adjoining walls. Not all sealant materials are suited for all substrate applications. Some sealants have better coefficients of expansion than others and are better suited for areas of high expansion/contraction. Roofing contractors get into trouble when they use the one-size-fits-all approach to sealants.
The success of the construction sealant is based on proper selection and use of the various sealant materials available for a specific application. Sealant selection should be based on the adhering substrates. General recommendations for sealant selection typical in roof applications are as follows:
- Concrete to concrete: Two-part polyurethane
- Brick to brick: Two-part polyurethane
- Metal to metal: Perimeter silicone sealant
- Metal to brick: Perimeter silicone sealant
- Metal to metal: Perimeter silicone sealant
- Metal to brick: Perimeter silicone sealant
Specific sealant requirements can be divided into two basic areas. The first is comprised of the universal properties that a sealant requires to be effective, and the second explains the process of proper sealant application.
There are three universal requirements that a sealant must possess to be successful. They are:
- Adhesion
- Compatibility
- Durability
A sealant’s performance in any joint depends on the adhesion of the material to the joint wall. The bond of the sealant/adhesive to the substrate must be strong enough to withstand stresses well beyond those that the joint is designed to encounter. The adhesion traits of most sealants vary depending on the existing substrate.
Another important attribute that aids proper adhesion is surface preparation. Most sealant manufacturers provide surface preparation instructions, particularly if primer is required. With all sealants, it is important that the surface be clean and dry prior to application. The sealant should be installed as soon as possible after cleaning the substrate, before the surface is contaminated with the dust and dirt from the jobsite. The best adhesion is obtained when the sealant is applied and tooled to completely fill the recess provided in the joint.
Whenever different construction materials adjoin, compatibility is always an issue. Different materials have different formulations. Signs of incompatibility range from slight discoloration of the sealant to loss of adhesion loss at the substrate. At construction joints, the sealants must be compatible with the substrate, adjoining sealants and building components. The sealant must also be durable enough to provide a service life equal to that of the adjoining components.
