Does Epoxy expand a little after curing?

[Martin Brandt]

Here's my question:  Does epoxy expand even a little after cure, even a micro amount?  I have had two deer leg bone handles crack longitudinally some time after filling with a hidden tang and epoxy.  I also had a white paper micarta handle crack several times, a year or two after glue up with a hidden tang as well.  This was a handle block that was drilled out for the tang.  The bone handles were clean and dryed for year or two.  I'm about to glue up a walrus tusk handle with a hidden tang, and I don't want a repeat of past cracking.  The walrus is from a very old cutlery piece, (antique), so it should be as dry and stable as possible.  Any thoughts/experience?

 

 

[Garry Keown]

It is not how dry the material is but how well sealed it is although it is best to stabilise any porous materialsas as without being completly sealed against uptake of atmospheric moisture you  may well get expansion of the material and  it expnds inward against the tang as well as outward toward the atmosphere and this is what can cause the cracking you may be experiencing.

[Martin Brandt]

Thank you Gary,   I hadn't thought about inward expansion of the material.  That shouldn't apply to the white paper micarta though.  This was some old White micarta, and I had heard there were problems with it back then.  Assembled the knife 25+ years ago.

 

[Gerhard Gerber]

Certainly haven't had 25 years to test, but I always thought we'd have cockroaches and micarta handles left after a nuclear apocalypse.

One exception would be paper micarta, but I have to qualify that was my own attempt, resin seemingly didn't seep into the paper well enough.

With the bone, my only guess would be the heat of the epoxy setting perhaps?

[David Weaver]

I would bet bone or antler will shrink and expand tending toward shrinkage over the long term. 

 

Wood will continue to move forever, but much less after the first few years. if something is critical, even as far as dried wood goes, I wouldn't trust it to avoid movement or shrinkage when it's two years old. 

 

I figured at some point, wood would probably become inert as the volatile gases come out of it over decades, but it just gets less reactive, not non-reactive. I bought a wooden hand plane made in England in about 1830 a few years ago and figured of all things, it would be inert enough not to crack in the US - and in the summer in western PA while it was humid at that. After surviving almost 200 years without cracking, it developed minor end checks and a couple of surface cracks in a matter of days. nothing that was a threat to its structure, but a surprise and a bummer given the difficulty in just making a copy that's already the same age. 

[Dan Hertzson]

If your plane was put into an air conditioned room the associated humidity levels can be pretty low, leading to wood shrinkage.  Of course not as badly as wintering in a space that has central heat and no humidification, but it can certainly affect the wood.

[Joshua States]

On 11/1/2022 at 9:52 PM, Martin Brandt said:

Does epoxy expand even a little after cure, even a micro amount? 

It depends. Different epoxy manufacturers have different formulae.
What epoxy are you using? 

There could be a number of reasons your handle material craked over time.

On 11/1/2022 at 9:52 PM, Martin Brandt said:

The walrus is from a very old cutlery piece, (antique), so it should be as dry and stable as possible. 

Many of us fail to realize that tusk is basically a tooth and it needs some moisture to be stable. Like bone, when ivory gets too dry it becomes brittle and shrinks. This shrikage leads to cracking.
No clue about the paper micarta, except to say that as @Gerhard Gerber pointed out, much depends on how it was made. There is a lot of "micarta" out there which is little more that some material layered with colored epoxy or an acrylic substance similar to the stuff they put on concrete around pools, which is then compressed together. The original micarta was infused with phenolic resin, which is a thermoset polymer. This means it is baked to fully harden and set.  This stuff is incredibly hard (think billiard balls). The limited availability of true micarta is one of the primary reasons I stopped using it.