How to properly put on DP420 Epoxy?

[mvly]

Here is what happened:

1st attempt:
Got DP420 Epoxy black on ebay. Applied it by sanding the aluminum dropout to expose the metal and epoxy Doc's Torque arm to the expose area of the aluminum. I allowed about 1 day cure. About 1.5 months later, it started to peel off my ebike.
I figured it was a fake, and went out to buy it from a reliable source,
http://www.grainger.com/Grainger/wwg/search.shtml?searchQuery=DP420+black&op=search&Ntt=DP420+black&N=0&GlobalSearch=true&sst=subset

2nd attempt:
This time, removed all the old DP420 stuff on the bike's dropout and applied it again. Did the same thing again, but this time, allowed 1.5 day cure. Now about 3 months later, one side started to crack. See picture below.

Am I applying this wrong? Do I need to wait a full week before I use my bike? Do I need more DP420 black? I know from building other stuff, to use minimal epoxy as if you put too much, it might make it weaker.

Keep in mind, I am using this torque arm on a full suspension bike with regen enable set to minimal regen strength.

 

[itchynackers]

IIRC, DocBass's method was to cure in and enclosed area (box) with a hair dryer blowing hot/warm air inside. So it needs to be cured in a higher temp environment.

 

[mvly]

Looks like I need 7 day for full cure. But he did say after 24 hours it should be 90% strength. So I know there is no need to heat it up unless you want full strength in 30 minutes.

I'll leave it for a week this time around.

http://endless-sphere.com/forums/viewtopic.php?f=31&t=29129

I will have to make sure both parts are cleaned this time around when I put on the torque arm. I'll try to sand it down a bit more also to expose the steel and the aluminum a bit more. I really don't want my bike to be out of commission the next time I do this.

 

[richmpdx]

It is hard to know what caused an epoxied joint to fail, but surface preparation is a likely consideration. The paint should be thoroughly removed and the aluminum somewhat abraded. Remove any surface oils with a solvent. Aluminum can oxidize relatively rapidly after being exposed to the air by sanding, so epoxy should be applied soon after surface preparation. It is important to not clamp the joint to tightly to avoid squeezing out too much epoxy. Hope your next effort works better.

Rich