Volume 40,   Issue 5                                 May  2005

PRACTICE MAKES PERFECT
A Simplified Guide for Quality Results
by Mark Daniels and Greg Moran

Choosing the correct products for installation applications can be a frustrating issue during installation. Doors, windows and curtainwall components must be viewed as pieces of a system that provides a weatherproof closure to the building envelope, while also providing physical access, light and ventilation into and out of the structure. 

Individually in the system there are many high-performance products including sealants, adhesives, flashings, weather-resistant barriers, frame materials, gaskets and glass. This article focuses on the installation process and related installation products, particularly sealants. When combined improperly, the results can be a disaster. Understanding the application and performance limitations of the products used will save time and money, and understanding industry best practices will ensure a quality job. 

Training
Proper training in installation techniques is a requirement—not an option—to ensure persons involved in installation are using safe and recommended installation practices. Training includes not only full-course offerings for first timers, but also refresher courses for industry professionals. While an installer may have great techniques for ease of application, he or she may not understand the longer-term effects of the technique. Though the installation may seem simple, poor practices may reduce the performance of the building material significantly. Resources include the InstallationMasters™ program, the Glass Association of North America, ARCAT for building product specifics, the American Plywood Association and the American Concrete Institute. Most window and door OEMs supply recommended methods with their products, usually available on their websites, and most component OEMs offer training and guidelines on how to work with their products.

The Jobsite Inspection
Step 1. Ensure proper construction before the installation. 
Inspection of the jobsite is critical for safety reasons and to ensure proper construction prepped for installation. Clear the area of unneeded equipment, tools and construction debris and make sure there are no hazards present. All fenestration products (glass, windows, doors, etc.) should be installed into an opening that is dry, clean and sound. Dry means no wet surfaces, clean means no contaminants such as oils, grease or loose dirt and sound means structurally acceptable. In the case of moisture a condensation barrier can develop between two materials limiting product performance. A glazing contractor may experience this when sealing wet glass into a frame. Surface moisture can create a barrier and limit the adhesion of sealants to the glass.

Step 2. Understand your substrates (i.e. building material). 
As much as industry professionals would love to believe sealants and adhesives bond to everything and under all conditions, they most certainly do not. Consider this: when applying sealant to copper should you prime the copper? If you answered no, then you likely will have to return to the worksite to reseal the product. The copper coating reacts with many sealants and will affect the cure rate of the sealant material. In effect the sealant could turn into chewing gum. For proper installation review the substrates with which you will be mating the sealants. Substrates exhibit different surface properties and may include wood, aluminum, painted aluminum, steel, vinyl, concrete and concrete block.

Choosing an Installation Sealant
Step 1. Choose a sealant that adheres to your substrates. 
Common sealant types include silicones, polyurethanes, latex (water-based) and silicon zed latex products. The chemistry of each has distinct advantages and disadvantages for specific applications. Don’t assume that all products will work in your environment or in your specific application. While manufacturers provide base data with their products, it is always best to review technical data sheets that list specific properties and limitations of the products. Always work with a reputable adhesive and sealant supplier to validate assumptions on adhesion to your substrates. If ever in doubt, ask questions specific to your use. Adhesion can vary based on the type of substrate, environmental conditions and application temperature of both the sealant and substrate surface. A quick check method for adhesion is to apply a 3/8-inch nominal bead of sealant to your substrate and then peel it back after a week cure time to determine initial adhesion.

Step 2. Always apply sealant using two-sided adhesion principles so that the sealant adheres only to parallel surfaces. 
Two-sided adhesion allows for joint movement that minimizes stress on the sealant and its adhesion bond line to the substrate surface. Three-sided adhesion creates pull and stress in an additional direction, limiting the elongation properties of the sealant material and possibly resulting in tearing and/or adhesion loss. For large joints, standard practice dictates the use of a proper-sized backer rod to aid in eliminating three-sided bonding and assuring proper sealant depth. 

Step 3. When possible, choose a solvent-free installation sealant. 
As a sealant cures, outgassed solvent can migrate to other building components, which can result in deterioration of the building material. Solvent-based sealants are widely used and, in most cases, do perform well. However, contact a solvent has to adjacent materials should be limited. Some self-adhered flashings are particularly susceptible to sealant incompatibility. In addition, higher solvent content leads to increased shrinkage of the sealant, resulting in gaps in the joint. The higher the solvent content of a sealant, the fewer the solids left behind when fully cured. Pay attention to solvent content and solids percentage ratings of sealant products.

Step 4. Choose sealant products with joint movement capability to meet your needs. 
Joint movement capability refers to the ability of a sealant to expand and contract. A common standard for measuring joint movement capability is ASTM C-719. The sealant is bonded to two substrates and allowed to cure. The sealant is then extended (stretched) and compressed over time to determine the materials movement capability. A +/- 25-percent joint movement means that the sealant can stretch 12.5 percent and compress 12.5 percent of the bead width used in the application. This is extremely important as all building materials move over time due largely to temperature and humidity variation, structure settling movement over time and seismic movement. Always use a recommended minimum bead dimension to meet the extension of the joint. The calculations will vary based on performance needs, substrates and geography. Bead thickness application recommendations are available from reputable sealant suppliers and generally differ based on what type of product is used for the application. When applying sealants remember that using more is not always better. 

As an example, consider what happens during daily environmental cycles to a PVC window installed onto a wood buck in a concrete block wall construction with stucco overlay. Wood and vinyl, as well as stucco and concrete block, exhibit distinct property performance sets related to temperature expansion and contraction, moisture penetration and surface irregularity. Will the chosen sealant need to flex over time and temperature cycling repeatedly? Absolutely. Choosing the correct sealant can mean the difference between a quality installation and water leakage. 

Step 5. Choose a sealant package system that works for you. 
Sealants and adhesives are available in several packaging configurations. The most common and recognizable package is a 10.3-ounce cartridge. Other options for the professional installer include 29-ounce cartridges and 10.3-ounce and 20-ounce unpacks commonly known as sausage packs. A key point here is that larger packages not only reduce the number of empty changeouts in the field, but also allow for uninterrupted beads of sealant.

An observation is that larger package sizes and dispensers weigh more. Advantages of sausage packs include improved shelf life, lower application costs and construction waste disposal costs. Keep in mind that each cartridge of sealant traps and wastes an average of 4 percent sealant in the plastic nozzle. A sausage pack dispenser has a separate removable tip that installs in the dispensing unit allowing for a one-time waste of up to 4 percent in the tip through the project. In addition, the foil sausage pack compresses into a small foil pancake for easy disposal space. Combined benefits of sausage packs could save thousands of dollars annually for large contractors. 

Step 6. Clean up. Always refer to the manufacturers instructions, not only for sealants but also for associated and installed products. 
Failure to recognize and understand clean up methods can lead to quality issues down the road. 

Step 7. Don’t be fooled by excessive durability labels and warranties. 
Review the technical information on products as listed above and find the products with performance levels that will adequately perform in your specific applications. The right products matched to the right application methods will perform as expected. In addition, check products for ASTM and AAMA qualifications, as well as federal specifications.

Know Who to Ask
Most manufacturers have dedicated resources to answer your questions. Most manufacturer websites include product reference and technical data sheets and in many cases there are specific references to the use of products. If you purchase products through a distributor, understand that you still have the technical resources of the component manufacturer, both through the web and the toll-free technical assistance number. It’s better to ask the questions in the beginning than deal with larger issues in the end. 

We encourage you to use these basic steps when making your decisions on installation and for installation products. The end result will be a satisfied customer and a quality and long lasting installation with reduced callbacks. 

The Authors:
Mark Daniels and Greg Moran are the product engineer and market field manager respectively for Sika Corporation based in Madison Heights, Mich.


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