Anyone have thickened epoxy do this?

Phil Nowack

Phil Nowack

Well-known member
So, I was snipping the wire stitches and the epoxy on one of the sides let go... actually it cracked at the joint.


I have not had this happen before...anyone else? And what may have caused this?
 
Yes, I had put it between the wires. This was two weeks ago. I was snipping the wire tonight, getting ready to do the final fillets and tape.
 
So, I was snipping the wire stitches and the epoxy on one of the sides let go... actually it cracked at the joint.


I have not had this happen before...anyone else? And what may have caused this?
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It wouldn't really surprise me all that much. Lot of stress in some of those panels. Although a lot of folks remove the wires ahead of filleting, and it usually works, I don't think it is a method Devlin promotes.

Bummer.
 
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I have always pulled prior to the thick epoxy...


Tod, the funny thing is that was next to no pressure on the two pieces of wood.... I was thinking that it was due to the temperatures. I was using heat lamps to warm the area and the heat the epoxy ....
 
I have always pulled prior to the thick epoxy...


Tod, the funny thing is that was next to no pressure on the two pieces of wood.... I was thinking that it was due to the temperatures. I was using heat lamps to warm the area and the heat the epoxy ....
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I've done it too and no prob, but I was always nervous. Did it let go when you were heating it? Epoxy gets soft and weak at pretty low temps that would be pretty easy to exceed with a heat lamp. I haven't measured the temps, but I'm guessing it gets soft as low as 150-200.
 
That is honestly my guess... it was near zero... and while I had tarps over it.. and heat lamps inside.. perhaps, there were too far from this spot...
 
That is honestly my guess... it was near zero... and while I had tarps over it.. and heat lamps inside.. perhaps, there were too far from this spot...
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Phil,
My first thought was it had to be temp related. I've not had much experience curing epoxy in low temps except for a fiberglass garage door repair many years ago. I was using poly resin for that project. Insufficient temp caused the poly to never completely cure. The surface stayed tacky and after applying more heat, it finally cured.
I wonder if in your case, the epoxy was warm enough to cure beyond "tacky" but not warm enough to cure to full strength.
 
Never had that happen Phil. I can imagine three scenarios that might have an effect on curing.

1) A bad batch of resin - what brand are you using?

2) Improper mix ratio or improper mixing though when this has happened it usually doesn't cure at all.

3) Temps too cold for proper curing. When I have had these conditions it just takes a long time to cure but I haven't noticed any degradation in the quality of the cured epoxy. You may have frozen your mix if the heat wasn't left on long enough or the epoxy got so thick from being cold that it never penetrated into the wood. Of all the above I suspect, like others have said, that the temps were too cold for proper curing.
 
I am going to have to dig out my book now.
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Please do and report back. I'm due to be wrong.
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Okay but I was planing to be wrong.
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I looked it up last night.... Devlin describes the tabbing method of making small fillets between wires and removing the wires, but says not to remove all the wires, but to leave some in for strength.

Either way a lot of us have removed the wires over the years and not had a problem. I know I removed all the wires from a bunch of areas on my snowgoose, but I'm pretty sure not all at once. I remember for my keel (which is not the highest stress joint) I had a really tight fit and just pored a couple cups of resin in it at the joint forward and let it run back in the "V" between the wires making a tiny fillet in just the gap. I removed the wires completely.

I don't know about the cold cure abilities of epoxy at the temps Phil is talking about. I always thought like Pete that in really low temps the cure would just be long, but I don't know if there is a threshold where the process doesn't progress. In the technical literature I've read, it has been a common theme that epoxy doesn't achieve full cure for several weeks at normal temps. At the low temps, it may just not have progressed.
 
Pete, I am using us composites. The entire batch so that I was using setup except for one side. My guess is that even though there was a tarp over the compartment and heat lamps in it, one side just did not get enough heat.perhaps I should not have tried to do this with temperatures routinely below freezing or should I say below zero.
 
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