Durability of Building and Construction Sealants
Author: Wayne Belcher
Founder and General Manager of United Professional Caulking & Restoration; Est. 1991. Certified presenter and educator for the Masonry Institute of Washington and the Western State Conference of Masonry Contractors.
More than just chemistry, ideally, the implementation of a sustainable sealant installation can benefit significantly from proper design assessment, sealant selection, and synergy on the part of the construction team. The basic requirements for the installation of elastomeric sealants are ever-changing and increasing as new and remedial construction technologies expand. As building techniques improve, training and education for the sealant installer is enormously essential to any sealant application and its anticipated performance. Each year, in commercial construction, residential, and remedial replacement, millions of gallons of silicones, urethanes, latex, and a whole host of differing types of adhesives and sealants are installed. Sealing materials take on a variety of organic and inorganic forms. Training for their installations rarely exists in construction apprenticeships, engineering, and architectural schools. Durability of building and construction sealant requires trained methodologies and knowledge of the fundamental mechanisms leading to their successful installations and performance. Without this training, high performance sealants will fail regardless of type, composition, characteristics, or published physically properties.
Liquid-applied sealants are installed manually in construction around the world to protect from water intrusion, destructive elements, chemicals, thermal movement, seismic movement, fire and much more. Sealant manufactures contend for market share with claims of superior advances in sealant technologies coupled with comprehensive warranties promising new performance standards, reduced construction schedules, and extended service life with greater than ever flexibility in project design and implementation.
Typically, a sealant manufacture will warrantee that their products are free from defects and that they will perform as tested. To ensure long term sealant warrantees extending to 5, 10, or 20 years, sealant manufactures require verifiable field testing; approved installation procedures, and substrate documentation prior to starting any new or remedial construction project. Recommendations for installing sealants from the manufacturer’s viewpoint are considered only an aid to proper applications, yet limited due to numerous substrate applications beyond their control.
Manufacturer’s published information should not be used in substitution for actual field/jobsite tests to ensure satisfactory results for the intended end use. Elastomeric joint sealant failures considered to be an applicator error or other forces beyond manufacturer’s control will not receive protection presented under a manufacturer’s warranty. Generally, but not limited to, sealants can fail as a result of:
- Poor Surface Preparation
- Lack of or Wrong Primer
- Excessive Bondline Stress
- Moisture During or after Application
- Installed Improperly
- Poor Tooling
- Poor Joint Profile
- Weak Substrate
- Movement During Cure
- Excessive Movement
- Wrong Sealant Installed
Applicator Knowledge, Training, and Experience
There is no debating that the sealant contractor is responsible for bringing a trained crew to the site and being sure that the employees follows proper installation procedures. The sealant installer must verify―that field conditions are acceptable for performance and installation of the work. Beginning the sealant installation constitutes acceptance of the conditions as satisfactory for the specified sealant materials. It may very well be that the sealant installer will be held responsible for the design selection and installation of the sealants, as well as the performance of the sealant system. If the sealant installer and/or contractor fail in installing the sealant exactly as indicated by manufacturer’s published literature [whether in print or electronically], then the failure is considered a construction defect, and therefore not covered under a manufacturer’s warrantee.
Notification of Warrantee Claim
When a sealant manufacture is notified to respond to a reported sealant failure numerous factors are considered and analyzed by the sealant manufacture. The specifics of the joint design and configuration must match up with the sealant’s movement capabilities in real field conditions.
If the joinery experiences sustained movement greater than sealants physical properties can deliver, the warranty will be invalid. To illustrate, the photo on the right is a specified urethane with a 25% ± promise of movement. The joint has experienced sustained movement greater than 25% causing cohesive failure, thus the warranty received by the owner is of no value for replacement and repair.
When Selecting a Sealant
The proper selection and use of a sealant is fundamental to its intended use, ultimate performance, service life, and durability. A sealant joint subjected to movement and other similar performance criteria should be designed for the particular application to avoid compromising its performance capability resulting in failure. If the sealant does not meet the criterion for a particular application, failure is more than a distinct probability and a manufacturer’s warranty will not cover the expense of replacement. The majority of responsibility falls either to the design professional, contractor, or sealant applicator.
General Joint Design
Sealants cannot make up for poor structural or joint design. Joint spacing must allow access for proper sealant installation, and if necessary, backer rod placement. Also, there must be sufficient bonding surface to adhere to once the backing material has been placed. For weatherproofing, a minimum depth of 1/4″ (6 mm) sealant/substrate bond, and (in most cases) minimum width of 1/4″ (6 mm) opening is necessary to ensure that sealant applied from a caulking gun will flow into the sealant joints properly.
Equally important is the proper selection and use of other materials and products associated with sealant use. These include substrate cleaner, surface conditioner or primer, type of sealant backing material, bond-breaker, and joint filler, among others. The ability of a sealant installation to remain watertight is critically dependent on proper preparation, building continuity, and durability of the substrates to which the sealant will adhere.
In some cases failure may be the result of the wrong sealant chosen for the job. The chosen sealant may be too high in modulus not allowing for the anticipated movement of the structure. The rigidity of the sealant results in undue stress on the bond line at high elongation. In very-high-movement applications (more than 25%), whether the sealant will fail adhesively or the sealant will pull itself apart (cohesively) or the sealant will pull the substrate apart (substrate failure), such results may be because the installed sealant was forced to extend beyond its intrinsic properties. The greater the distance the sealant is stretched, the greater are the forces on the bond line. Thus, forces at the bond line may be greater than the specified sealant was able to tolerate.
Poor cleaning is another primary cause of adhesive failure and loss of material warranty from a workmanship point of view. This has many aspects aside from the simple and often true statement that the worker just did not do a good job.
Since job site conditions of all kinds can affect the performance of joint sealants it is imperative that before the installation of the sealant begins that the joinery is examine with the Installer present, for compliance with requirements for joint configuration, installation tolerances and other conditions affecting joint sealant performance. Installation of joint sealant should not proceed until ALL unsatisfactory conditions have been corrected. Most commercial caulking contracts makes the caulking contractor RESPONSIBLE for ALL existing conditions at the moment of beginning the sealant work. Ignorance of other building envelope specifications is no excuse and all unsatisfactory and defective work encountered may be at the sealant contractors expense.
When dealing with any problematic sealant installation, it is doubly important to understand the root causes of the issues faced so a repair recommendation can accommodate the underlying dynamics that are identified. This level of detail is not commonly found in manufacture’s standard technical literature for most materials.
The success or failure of the sealant often depends on the attention to detail by the installer himself, not the manufacture. The skill and education of the installer in the field is extremely important.
This acquired skill and education is extremely important, for the sealant applicator must not only know the performance characteristics of the sealant material, i.e. compatibility, durability structural and non-structural applications, but also become familiar with a wide variety of substrates and how to prepare them to successfully insure good performance.
Today, sealant is a minor item when the cost of a building is considered. It has none of the glamour or impact of structural concrete, structural steel, heating, air conditioning, design, solar loads, and many of the other considerations that go into a building’s design and construction. Thus, the importance of sealants is often overlooked, and the subject rarely appears in the curricula of architectural and engineering schools.
If the design is good and the sealant lives up to its promises, then the responsibility for a good seal falls to the applicator. A successful and warrantable sealant installation requires the right materials and proper installation. The best protection to sealant installations is the eventual certification of sealant applicators, or the credentials to indicate that the worker has mastered the basic skills.
United Professional Caulking & Restoration Inc.