G-Flex epoxy test

Until now the only epoxy that I've found that works well with polyethylene has been 3M ScotchWeld DP 8010. Its bonding strength and structural characteristics are amazing but it's a little difficult to work with (short work life of 5 minutes, and 10:1 mixing ratio requires good precision).

Some of the forum members have mentioned West System G/flex 650 as an alternative. It claims to work on PE and has an advertised work time of 45 minutes and a 1:1 mixing ratio so small jobs could be done with small batches without rushing. Sounds great for some boat projects I had in mind. So I picked some up at West Marine ($20 for 8 oz.).

But first I decided to test it out on some scrap to see what to expect. For the first test I ignored the instructions and glued 2 clean untreated Hobie sample disks together to get a feel for initial strength. (This simulates a specific remote reinforcement to the rudder zone of the Adventure Island). After curing, the disks broke apart about as easy as snapping a cracker. Not a good omen (the 8010 made a very strong bond under a similar test).

For the second round I coarse-sanded and cleaned the disks with alcohol as directed.


After curing 24 hours, I again pulled the discs apart. The glue had about 3 times the bonding strength as the first test but was way short of what I needed. Nevertheless the improvement does demonstrate the value of good preparation. There was no great effort involved in separating the discs again. Here you can see the poor bonding.


In this final picture, the glue peels easily from the remaining disc.


Very disappointing. With this level of preparation the 8010 has been reinforcing my severed cam columns for 2 years now without any sign of separation or failure.

G/flex does recommend "flaming" the surface of PE for a stronger bond, but many applications are inaccessible to this process, especially inside the hull. So I didn't bother getting the torch out.

I would say the G/flex is no better than most other epoxies on PE and is vastly overrated. For high strength bonding with PE it is useless without a flame treatment, and I'm frankly a little skeptical about that.

At least that still leaves the DP 8010. Any other recommendations?

Hi Ya RR
Here's my recommendation " If its not broken dont fix it".
Some adhesives work better under tension rather that shear as was explained to me once by an industry rep. Thanks for the test. I will use the 3M if ever needed.
Kepnutz

Thanks for the comment Kep -- good advice!

Here's an update. I went ahead and flamed the samples (just passing the torch over quickly) and re-glued. There was a definite improvement. The break apart effort was at least 50% greater and the residual epoxy did not peel off as before. It ended up being a decent bond -- certainly nowhere near the strength of plastic, but enough to hold accessories and effect repairs requiring a substantial, but not full strength application. I wonder if flaming PE surfaces has the same effect on other epoxies...?