Tightbond III
I have an engineer friend at Franklin International, the makers of Titebond glues. I asked him his opinion of using Tightbond III on canoes and below is his response. I have not included his name or number but would be happy to pass it on to interested people through a PM. He does speak of epoxy covered canoes which usually isn't 'what we do' but his information I think is helpful.
-Chuck
Dear Chuck,
I do not recall that specific exchange, but this topic comes up regularly. I am quoted on a regular basis because part of my work is on the public end of this company, and you are more than welcome to do so. My only request is that my statement remains intact to avoid any confusion out of context.
Titebond III is not recommended for applications where continuous submersion is entailed, not because it will fail but because it raises the question of liability. Since wooden canoes are normally finished with CPES and/or several layers of epoxy, virtually every type of wood glue has been used successfully. This includes the most basic white glues, which offer no water resistance, and they hold together because as long as the epoxy remains intact it will not be exposed to water. It has been argued that even if damage does occur, it is unlikely to result in catastrophic failure because the process of dissolving the glue takes time. Canoes tend to spend more time out of the water than in it, so scratches are typically repaired before any damage can propagate through the glueline. Cross-linking or catalyzed PVAs such as Titebond II or Titebond III feature high levels of water resistance, although when completely saturated with water they will lose strength until they are again fully dried. Our specific recommendation is to use marine grade epoxy or other resin based adhesives for this purpose. We are fully aware that Titebond II and Titebond III are both commonly used in this application, but that this is a calculated risk on the part of the end user.
This likely brings up another common question: What is the difference between Titebond II and III? Products are often designed to pass specific tests, and such is the case for both of these products. Titebond II exceeds the requirements of ANSI/HPVA Type II water resistance, which Titebond III exceeds the requirements of ANSI/HPVA Type I water resistance. Both of these tests are conducted using 6” x 6” birch laminates glued together to make three-ply plywood.
Type I testing involves cutting the 6" by 6" assemblies into 1" by 3" specimens, boiling them for 4 hours, then baking the specimens in an oven at 145°F for 20 hours. Next, they are boiled for an additional 4 hours and immediately cooled using running water. The specimens are sheared while wet, and the bonds must pass certain strength and wood failure requirements to pass the Type I specification.
Type II testing involves cutting the 6" by 6" assemblies into 2" by 5" specimens, soaking them for 4 hours, and then baking the specimens at 120°F for 19 hours. This is repeated for a total of three cycles, and the bonds must not delaminate in order to pass the Type II specification.
Rather than simply being a better or worse product, Titebond III is different from Titebond II. While Titebond III is capable of withstanding boiling water, it has greater thermal plasticity in lower temperature ranges. For instance: we test our wood glues for shear strength using hard maple at both room temperature and 150°F. At room temperature, both products are stronger than wood and therefore indicate the shear strength of maple, which averages between 3200-3400 PSI. At 150°F Titebond II loses roughly half of its’ bond strength and Titebond III loses nearly 2/3rds. Since creep correlates directly with thermal plasticity, it is evident that Titebond II has greater resistance to mechanical creep than Titebond III.
Please feel free to contact me
