by Marthe Sandvik, CSI, CCPR, ChemRex, Inc.
Correctional facilities, some medical facilities, and high schools provide a demanding environment for finish materials. Some, such as concrete and masonry, are naturally resistant to damage, but others are easily destroyed.
Joint sealants are particularly susceptible to vandalism, as they are among the softest products used in construction. In most situations this is not a problem, but those sentenced to confinement have a lot of time and little to do but figure out ways to destroy their surroundings. Some prisoners have also discovered that by carefully removing a joint seal, they can hide contraband in the joint and replace the seal. Probably something they saw on "Hogan's Heroes".
The table shows approximate values for a select group of sealant characteristics. The standard urethane and silicone sealants used in construction are soft, have relatively low tensile strength, and are able to stretch a lot before breaking.
The security sealants show significant increases in two properties: hardness and tensile strength. You already know how soft standard sealants are; for comparison, the epoxy sealants are similar to tire rubber. Increased hardness means the sealant is more difficult to cut or dig into; greater tensile strength means that it is more difficult to even if someone does manage to get a grip on the sealant.
There ain't no such thing as a free lunch, though; the gain in vandal resistance comes at the cost of reduced allowable movement. While most commonly used joint sealants accommodate joint movement of plus or minus 25 percent, manufacturers recommend that the urethane joint sealants be used only where joint movement is 12-1/2 percent or less to reduce stress at the bond line. Joint movement isn't even discussed for the epoxy sealants.
Regardless of the application, be sure to consider all performance sealant characteristics. In general, sealants with high tensile strengths will have lower capacity for movement. They will also tend to fail in adhesion instead of cohesion, i.e., the bond to the substrate will fail before the sealant breaks.
For security sealant applications, then, consider the urethane security sealants for moving joints, and be sure the design provides enough joints to keep movement under 12-1/2 percent. The epoxy sealants should be used only for non-moving joints, e.g., around interior door frames, or around wall-mounted fixtures.
Marthe is the Midwest Strategic Accounts Manager for ChemRex, Inc. She also represents Sonneborn, Thoro, Hydrozo, ThoRoc, and Master Builders. Call Marthe at 651-779-7091, or send e-mail to MBSandvik@aol.com. See Marthe's article, "Sealants for Masonry" for more sealant information.
© 2000 Marthe Sandvik, Sheldon Wolfe