Q&A Jop-Site Glues

Glue Test

We tested nine glues for strength: construction adhesive (MACCO's Liquid Nails heavy-duty construction adhesive), contact cement (DAP Weldwood), cross-linking PVA glue (Franklin International's Titebond II), cyanoacrylate (Pacer Technology's Zap-A-Gap), epoxy (System Three Quick Cure), hot-melt glue (generic general-purpose glue sticks), polyurethane glue (Gorilla Glue), white glue (Elmer's Glue-All), and yellow glue (Franklin International's Titebond). The simple testing protocol used common tools, not laboratory testing apparatus. We glued together nine pairs of 2x4 blocks, 6 inches long, applying the glue to only 7 square inches of each test assembly. (Each 2x4 face received a 1-inch-wide strip of glue on either end.) Before the glue-up, each 2x4 block was fitted with a 1/4-inch eyebolt with a countersunk nut and washer (see Figure A). All of the glues were applied according to the manufacturer's instructions. After clamping for up to two hours, the blocks cured for five days at about 70F.

Figure A. Nine pairs of 2x4 blocks were fitted with eyebolts and glued together with different glues.

The test was set up as a series of elimination rounds, somewhat like the TV show Survivor. In the first round of testing, each of the nine test assemblies was suspended on a chain and weighted with an increasing number of 42-pound concrete blocks, up to a total of four blocks (Figure B). This round eliminated two glues (Figure C).

Figure B. The test blocks were suspended on a chain and gradually loaded with an increasing number of concrete blocks.

Figure C. The first test sample to fail was glued with contact cement. The joint began to separate when loaded with three concrete blocks.

For the second round of testing, the surviving seven test assemblies were soaked underwater for 24 hours. Then they were again weighted with an increasing number of concrete blocks (up to five). This round eliminated one glue. In the final, brutal round of testing, the six surviving samples were linked together, chained to a maple tree, and pulled apart with a come-along. Two glues were eliminated by this test. When the hardware failed (the eye-bolts eventually opened up), the test was declared over, leaving four winners (Figure D).

Figure D. The last six glue samples were fastened to a maple tree and tugged with a come-along (left). Two failed, while four survived until the eyebolts deformed (right).

Although this test was intended to measure glue strength, it must be emphasized that the strongest possible glue is not always the best glue. A glue only needs to be strong enough to perform the job it's used for. Furthermore, if a glued joint never gets wet, strength after soaking is irrelevant.

The Results: The Bonds That Held
Round One:	Samples weighted with concrete blocks
1st Glue Eliminated:	Contact cement (Failed when weighted with 3 blocks)
2nd Glue Eliminated	Hot-melt glue (Failed when weighted with 4 blocks)
Round Two:	After soaking underwater, samples weighted with concrete blocks
3rd Glue Eliminated:	Construction adhesive (Failed when weighted with 4 blocks)
Round Three:	Samples linked together and pulled apart with a come-along
4th Glue Eliminated:	White glue
5th Glue Eliminated:	Epoxy
The Winners:	Titebond, Titebond II, polyurethane glue, and cyanoacrylate

Nevertheless, some general conclusions can be made. Common hot-melt glue forms a relatively weak bond. Household white glue is surprisingly strong, even after 24 hours underwater. And yellow glue, polyurethane, and super glue are so strong that in most cases, the materials themselves, or the hardware attached to them, will fail before the glue joint. -- Martin Holladay