March 2007

Dr. Dave Dunn

Question: Can you recommend a sealant that will stop pinhole leaks in an old fire sprinkler system to give us more time before we have to replace the entire system?

Answer: Some companies sell two-part epoxy adhesives that are fast curing and designed specifically for repairing this type of leak. In fact, you can buy kits comprised of an epoxy putty stick plus an impregnated fiberglass tape. Another product worth trying is a low-viscosity anaerobic methacrylate liquid that will seal many pinhole leaks. In order to use this, you have to empty the pipe of water and dry it thoroughly. Heat the pipe using a flame or hot air gun and then apply the anaerobic. As the pipe cools down, the liquid will penetrate into the porosity and then cure. New technology that will coat the inside of fire-sprinkler piping with an epoxy lining - thus avoiding replacement of the piping, in many cases - is just becoming available.

Question: We use a two-part epoxy adhesive to bond steel laminates together. Can we use heat to fixture the parts faster and accelerate curing?

Answer: Yes, the use of heat to speed up the curing of these adhesives is very common. Two-part epoxies that fixture in 30 seconds or so can, in fact, be purchased. While this is ideal for the rapid assembly of small parts, it is not convenient for the assembly of complex parts. If your parts don’t need clamping, then heating them up with a heat lamp or in an oven will probably be the best solution. The manufacturer of your specific adhesive can give the best recommendations for best temperature and time. If you need to fixture the parts quickly, then the rapid application of a lot of heat energy can often achieve this. Induction heating has been used to achieve this, such as in the bonding of golf clubs, but you can also do it with localized application of heat with a hot air gun to achieve temperatures of 250-300°F. This will give fixture times of 20 seconds or less, and the adhesive can then achieve full cure at room temperature.