BUY SYSTEM THREE T-88 STRUCTURAL EPOXY ADHESIVE AT YOUR PERIL.
To make these coaming corner posts each side required 3 pieces of 1 1/2" x 6" x 15" to be glued up into a single block of approx 4 1/2" X 6".
There are not many wood glues available for exposed exterior wood pieces. The only wood glue we can truly depend on is Resorcinol.
It is an formaldehyde powder/purple resin mix that is impervious to everything when bonded including water immersion and delamination. It needs careful measuring, controlled timing, controlled temperature, and extreme clamping to be successful. it leaves a prominent dark purple glue line. Not something desirable on a mahogany glue-up for the coaming posts at the cabin. So I thought!
Another is powdered urea-formaldehyde 'plastic resin' glue, mostly tan colored and activated by mixing with water.
It is water resistant, will not take immersion. But it leaves a lighter colored or no line at all and is often used for wood masts, spars and laminated tillers. It also requires pressure while curing. It is a little more forgiving with humidity and temperature. Generally these glues have trouble setting under 60 degrees ambient.
I would describe these glues as producing a chemical bond with the wood - while the next choice produces a mechanical bond. That is if it's not T-88.
The third choice is epoxy adhesive. My bloody choice. I have used Smith's 2-part Allwood and Tropical epoxy for years without failure. It says it will glue oily woods such as teak - and it does. T-88 makes the same claim. Laminates are put together with moderate pressure so that the glue does not all get squeezed out to starve the joint. Good epoxy is even more forgiving of humidity and ambient temperature. It's the only choice when the project temp is below 65degrees.
Structural epoxies are not laminating epoxies which are usually runny and engineered for fabric wet-out. Adhesive epoxies are stiffer, thicker, and smell mildly of toast and ammonia. Guess they are low VOC, nearly 100% solids, and are not waterbourne.
It was time to try a fresh system so I ordered SYSTEM THREE T-88 STRUCTURAL EPOXY ADHESIVE.
www.systemthree.com
It mixes just like Smiths Tropical Wood Epoxy: it is a viscous material that spreads easily because it kind of likes to hold together. Quite different than laminating epoxy which flows apart like pancake syrup. On the freshly milled mahogany there seemed to be quick wet-out . The glue was applied liberally with a toothed spatula to both sides of each joint. No holidays. The pieces were smooched together and squared up with clamps at right angle to the glue line and weight was put on top. Can't remember what weight but might have been tool boxes. The result IS a consistent 1/3mm glue line.....
DISASTER!!!
The coaming blocks have failed.
THE GLUE LINE IS PULLING APART
Barely noticeable across the top end grain the two glue lines are opening. So far only the wider top of the post is coming apart.
Have not yet pried at the joints. The wood may be moving because of hot weather and drying winds - the pieces have not spent time in the sun. The WOOD at the joints is not splitting -
just the GLUE is letting go!
The end grain of the wood is totally tight, not the slightest crack.
The whole point of this adhesive is to hold the wood pieces TOGETHER
NO MATTER WHAT.
DON'T BUY SYSTEM THREE T-88.
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You have to take my word on this one.
I've worked epoxies for decades.
Was extra careful with this project. Mah baby.
No solvents were used to prep the wood surfaces.
The mahogany has been covered and stickered dry and air dried for 30 plus years.
Honduras is not known as a problem wood to glue.
Freshly planed, milled, toothed for epoxy to grip.
The pieces were sequentially stacked as cut.
The two-part T-88 carefully measured, carefully mixed.
The method used is to turn the two parts together on a square of acrylic sheet with a two inch spatula/knife. Excellent and thorough.
The glue was not mixed in a cup.
After mixing it was allowed to rest for 1/2 hour.
Then applied to room temperature mahogany.
and the pieces smooched together wet on wet.
What did I miss?
As far as I'm concerned this is a failure of
S Y S T E M T H R E E .
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Good Cod, and I just got started using their waterbourne LPU in the cabin.
And I thought also for the coach roof outside.... maybe it's garbage too?.....
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