...continued from previous page
Sealants, Caulks, Caulking Guns
Selecting a sealant requires an understanding of the joint: the width and the amount of movement expected. Sealants are tested to federal specifications or standards set by ASTM.
by Ray Heck
Early products had their good points as well as their negatives. Acrylic technology at the time was not state-of-the-art as it is today. Acrylic caulks have been expected to bridge cracks and to dissipate movement without failing. This was accomplished by blending the day’s current technology: vinyl-acrylics and a lot of plasticizers. This made for flexible caulk beads, but they suffered from a high degree of dirt pickup and plasticizer migration that left the caulk bead brittle after exposure to time and the elements and ultimately lead to failure.
Acrylic resins are the backbone of the caulk. Today, resin manufacturers have made great strides and brought all-acrylic internally plasticized resins to the caulk manufacturer. These new resins have a high degree of flexibility and elongation. Because of these attributes, higher quality acrylic caulks can bridge cracks, spanning the gap as it opens and expanding and recovering (memory) as the crack contracts. Silicone adhesion promoters, found in many C834 grades, exhibit better adhesion, weather well and are extremely durable. 100% acrylic caulks are also more resistant to the effects of high alkalinity.
On the low end of the acrylic caulk spectrum you’ll find products of fair quality. To lower the cost they are frequently loaded with inexpensive fillers that do not offer a high degree of performance. Failed projects can often be traced to these products used in the wrong application.
Another factor to consider is warranty life. Many caulk manufacturers will label grades anywhere from “15 Years” to “Lifetime performance.” Many purchasing decision are made on two data points, cost and “Warranty Life.”
Year designations have typically followed testing specifications and protocols. Lifetime or 50 Year products usually carry the ASTM C920 Class A or B, as well as the TTS-230 specification. The greatest volume in the industry is 35- to 45-year caulks, which will carry ASTM C834. These products are tested at 0° C and -18° C. If your caulk application will be subjected to a wide temperature variant, the ASTM C834 at —18° C should be utilized.
Year designations do not guarantee performance or longevity. The applicator needs to make a selection based on the requirements that will be placed on the caulk. When checking the information on the tube, read what the product has been tested for. Do not be misled by statements such as, “meets the performance requirements of ASTM …” If the information is not the caulk tube, contact the manufacturer about the product you intend to use. Their technical departments will share test data with you so that you can make a more informed purchase.
Even the best caulk can’t do its job if applied to a substrate that’s covered with oil, dirt or other types of contaminants that can prevent proper bonding and curing. The substrate must be prepared properly. It should be sanded, dusted, wiped or wire-brushed. Make sure it is clean and dry.
Joint size is also critical. The caulk should not be applied when the joint has expanded or contracted considerably because of temperature. Look at the percent of movement the sealant can take and compare it to the joint size. If the joint is greater than 1⁄2" deep and 1⁄2" wide, it’s important to use a backer rod in the joint. The backing material maintains the optimal sealant thickness. It also prevents the sealant from making a three-point bond, which can lead to caulk failure. Joints this size may require the use of silicone or polyurethane caulk; you might want to check with the caulk manufacturer for a recommendation on the suitability of an acrylic product for joints this size.
Cut the tube’s tip slightly smaller than the width of the gap. Run a continuous bead whenever possible. As a general rule, keep the bead slightly ahead of the tip to eliminate air pockets or overlap that will create an imperfect joint.
Position the gun so the sealant gets forced into the gap. Pushing or pulling the gun along the surface is acceptable; keep the bead smooth with good contact to the substrate. Don’t go too fast and practice on scrap before beginning.
Once the caulk is in place, tooling may improve surface adhesion and appearance. Don’t use a solvent when tooling. Excessive tooling will remove too much caulk and will typically lead to caulk failure due to insufficient material in the joint.
The curing process depends upon the sealant and the ambient temperature. Check the label for proper cure times before painting. If you have any questions, contact the manufacturer’s technical service number for additional information.
For years, the caulk and sealant industry has been full of “me-too” technologies and minimal innovation. However, owners and painters demand and expect high performance products. Acrylic binder suppliers are allocating funds for the development of new and improved acrylic resins, and innovative manufacturers are committed to delivering value and performance with these new technologies.
Ray Heck is sales and marketing manager for Lighthouse Products, a division of GE Sealants & Adhesives. An industry veteran with almost 25 years of experience, Heck says he has “been fortunate to work for several of the coating industry’s top leaders and benefited from my relationships with them and the experiences they shared with me.”