GFlex Expands more than regular epoxy?

[chuckt]

I routed and filled my topside plank seams with epoxy and filler. (1950 Chris Craft Cruiser) On a couple of seams I used GFlex as an experiment thinking it might last longer than regular epoxy. I've noticed in the hot weather that the GFlex filled seams show through the paint very slightly as if the G-Flex expanded. I didn't think about increased flexibility equating to greater expansion when heated. Anyone notice this or can confirm this is what is going on? It is very slight and doesn't bother me (much). But, if the regular epoxy holds up as well, or nearly so, I don't think I will use the GFlex for this job again.

I'm not looking for commentary on whether it was a good idea to route and fill my topside seams but if you must . . .

[JimConlin]

Call West System tech support 866-937-8797 and let us know what they say.

[Todd Bradshaw]

I suspect it's some sort of creep thing (not a creepy thing). One of the things that allows G-flex to do things that regular resin can't do well is its more flexible nature. As such, it is less able to overpower the tendency of wooden pieces to expand and contract with weather changes. Just a one percent dimensional increase in a long hunk of wood due to humidity and temp can be a surprising amount of movement. The G-flex may be able to absorb this without shearing away, but it's probably going to leave a mark (stretch mark?) when the wood moves back. The brute strength and more rigid nature of regular epoxy has more ability to stabilize the structure, as long as the wood isn't so thick that it can overpower it. This is one reason that the best wood/epoxy boats tend to be made from thin layers of wood, connected with epoxy, as well as reasons why trying to stabilize a 2" thick hunk of wood with a couple coats of resin and/or fiberglass usually fails and why flexible epoxy is not a great choice for holding stressed panels (like stitch and glue boats with bent sides) together. Too much creep.

[chuckt]

Todd--I didn't think of it that way--I bet you are right. The wood is expanding and the more-flexible gflex is pushed out just slightly. It will be interesting to see how prominent it is when the sun is beating hard on that side.

[JimConlin]

I'd wonder whether it's a permanent deformation in response to a steady load (the definition of creep) or elastic deformation that'll spring back when the planks shrink and the pressure is relaxed.

I expect that the Gougeon folk have done these tests.