by Randy Zajac
It all started when I got a tech call from somebody asking if WEST SYSTEM® 105/206 would accept a nail pounded into it, after it was cured, with no pilot hole. I confidently said that it would not work well and in most cases, it would fracture the epoxy. Just for fun, I went out in the shop and tried it because even though we all pretty much agreed it wouldn’t work, nobody had ever actually done it. Well, we were right—the nail caused a “brittle” failure.
Then I saw a 1/8″ thick piece of cured G/flex 650 epoxy sitting on my workbench that I had left over from another test. Once again, just for fun, I pounded a finish nail into the surface only to find out that it took the nail and didn’t crack. Thinking it was a fluke, I did it again with no failure. At this point, I decided to do some tests with more controlled attention.
I cast a sample that varied in thickness up to ½” onto a piece of ¾” plywood. The sample took 8 nails at five different thicknesses along the sample without cracking. The sample also took 6 drywall screws at different thicknesses with no pilot hole. To rule out the chance of this property going away as it cures further, I put the samples in an oven at 120°F for the weekend. I took the samples out and let them cool back down to room temperature. When I tried again, all was the same as before–no epoxy failures.
Looking for the next step, I visited my uncle’s furniture reupholstering shop. All of the samples took a 7/16″ staple from an air gun, plus #4 and#6 tacks (think square-cornered wedge) without cracking. G/flex is now used to fill frame members on furniture that has been reupholstered so many times that the wood is falling apart and won’t hold a fastener.
Not only did these tests provide valuable data on the G/flex toughness, flexibility, and impact resistance, they gave us a great visual demonstration of what toughness is.