Glueing epoxy parts

I use a good 5 min epoxy for most of my bonding. When I use it on epoxy parts that I have made(room temp cure) I have no problem with it sticking. On the few occasions I have had with epoxy parts I have purchased like fins and keel trunks it doesn’t seem to stick that well. I sand the parts with 80 grit beforehand so I should have a good bond but I have had a few joints break. Any explanations, hints?

Hi Don,

Don’t use 5 min epoxy!

Seriously, I slow epoxy for construction. I find that 30 or 45 min epoxy works. In my experience, 5 min epoxy never sets up hard.


Don - I concur with John in his assessment. For me, 5 minute stuff always “feels rubbery” when cured.

Generally I will use CA for tacking parts to hold quickly, and follow with “neat” epoxy on all seams or bulkheads and then follow with a fillet of slow epoxy mixed with either silica for strength, or micro-balloons if just to support. Haven’t found much of a need for 5 minutes - too many other things to do while the slow cure stuff kicks off. [smile]

Shameless plug for West System products. !!

+3 on not using 5 min epoxy. If you really want good 5 min epoxy not the cheap stuff, west systems does make a 5 min version that is truly 5 min cure. They even say dont use it for structural loads. They make a slow version that has flex as well for higher loaded joints.

Hi Don,

Just out of interest- when the join fails there are several things that can go wrong.

Could you tell me if the epoxy itself failed, and the bond line was intact, or if the bond line failed and parted company with the items it was supposed to anchor in place.
This might help me explain what happened and why…

As a general rule 5 minute epoxy is for temporary repairs and not suitable for long term high load applications.
I have seems it break down in high humidity conditions especially where salt water is concerned.



Also, I would wash the parts with Top Job to get the mold release wax off. Most people that sell unfinished molded parts do not wash them. The higher viscosity and faster cure time (less time to penetrate) may account for some of the difference between slow cure and 5 minute epoxies.

+2 on not using fast cure epoxy. Even 15 minute epoxy is much better than 5 minute.

Unfortunatley, I have already re-glued with regular epoxy and a layer of cloth so i can’t see the joint any more. I have used 5 min for just about every joint in my boats for 10 years and have had no problem except for commercial parts. I first noticed it with the graphite fishing rods that I used to use for masts. If you could hook your thumbnail under the epoxy it would peel right off. I sand all my joints. Gregg may be on to something. Maybe the sanding doesn’t get all the mold release and I should be chemically cleaning them first.

Hi Don,

No problem… It sounds like the epoxy is not bonding with the base material.
After sanding, do you clean the surface so it’s free of particulates and/or contaminates?
The best and easiest product I have found to use is brake cleaner in an aerosol format.
Very, very convenient and you get a nice clean bonding surface.

Maybe worth a try…

Cheers, Jim

Hi Don -

a co-worker built a PeaPod (stitch 'n glue) using 5 minute epoxy from big box home center. After gluing up the hull and deck he removed the wire ties, and glued in the keel and had it near his fireplace. Big “POP” and all epoxy let loose at most glue joints. We assume it was too warm, and regardless - he switched to marine grade epoxy even though more expensive.

Just thought I would mention. Sometimes the syringe 2 part stuff works - sometimes NOT. If you use WEST I had posted several times a way to do very small amounts without using a scale. Basically wax paper over a print out of 5:1 circles. If you keep themin that proportion, regardless of size - it is still a 5:1 mix and cures as always. Just don’t have to fool with scales, mixing tins, etc. Mix right on the wax paper. I usually use a $.50 size and another the size of a $0.05 which gives me just small amounts without worry of pump strokes. Drop resin on big circle and then drop hardener on small circle. Correct mix and not had any failures. Just a quick step and seldom any waste. WHat there is is tiny. You can always mix in silica or balloons once initial mixing is done. I use a popsicyle stick and just keep adding small amounts until consistency I want is reached.


Here is master (for those who may have missed earlier postings).
Print out and use a copier to enlarge/reduce as needed. Was published by Gougeon Brothers in one of their magazines so if you use big circle for RESIN and small circle for HARDENER - you should be OK.