i think it would be a really interesting experiment if you repeat it without using wood-flour thickened epoxy. just use an unadulterated epoxy disk.
or if you still have some of your dry wood-flour/epoxy mix left, to let it soak in water and let us know your result.
i am wondering if the wood-flour itself is what is being effected by the soaking in alcohol. the water-proofing (and i assume alcohol proofing) capability of epoxy is based on epoxy resin of a certain minimum thickness.....and even then for only a certain amount of time before the epoxy itself actually conducts water through.
i have a bit of experience in barrier coats and fibreglass hull repair/osmotic blistering and the like.
so i am thinking/wondering if you simply conducted alcohol into the wood flour. i say that becuase when i mix up 'peanut butter' consistency wood-flour epoxy....it is less dense than pure epoxy....which seems to imply that the wood particle is coated....but is actually dry inside. and the alcohol, may be leaching into wood and changing the property of the epoxy/wood-flour mix which may explain the result you are getting.
As luck would have it I have been glassing the interior of my Yawl this week and had a trashcan full of hardened clear epoxy. I went out and dug down to the bottom for the oldest solo cup with an epoxy disk on the bottom, pulled the brush with the epoxy on it like a popcicle out of the cup and plunked it into another cup filled with denatured alcohol. Within an hour the brittle flakes and shards around the edge of the dick had softened into a rubbery clear substance that crumbled when rolled between the fingers. The solid disk has softened to the point where I can easily scrape it away with my thumbnail and leave a gouge about 1/16" deep in the surface. The removed material is jelly-like.
Denatured alcohol softens cured epoxy. Period, no doubt about it. Before anyone starts to quote the literature at me, just try it yourself. Do the experiment first before you deny that this is happening. This effect happens, it is real.
I'll back that up. I'm also using Kleen-strip alcohol on MAS epoxy. It takes a while for the alcohol to have an effect, so I never noticed it when just wiping the surface with a rag since even small puddles evaporated too quickly. But, if you soak the epoxy it definitely softens it. The epoxy hardens again when it dries out, but I would be curious to know if it loses any strength as a result.
Forgot to add, that with regards to solvents, impervious doesn't always mean "totally unaffected by." For example, with chemical gloves if you read the spec sheet the manufacturer will list all the different solvents that glove is effective against, and the breakthrough time for each one. You'd probably have to go back to the spec sheet for the epoxy and find out what the breakthrough time for alcohol is for a given film thickness and if there are any permanent effects on the epoxy. I'm going to go out on a limb and say there's probably nothing to worry about unless you plan on sailing on a lake of denatured alcohol (which I would advise against for other reasons anyway).
wow....had never really dove into this....thanks chester for the experimental results.
in all the things we do, i suspect there are some things we just pick up, they appear to work, and we don't get into the phsics or chemistry of it....and some things that catch our interest and we do a deep dive.
so i spent some time this morning doing a literature search on the topic and i think psimian probably described it best.
denatured alcohol is clearly a solvent that interacts with epoxy (in some cases used as a thinner)......albeit a relatively weak solvent compared to acetone and other solvents that came up in my read.
that said, used as a quick wipedown on a fully cured surface, it should evaporate quickly and does not appear to be a concern to any of the major manufacturers who happily endorse an alcohol wipedown as part of the surface prep instructions for re-coating a cured surface.
i think what was interesting in what i read was the number of physical factors that come into play when working with epoxy. for example, i was reminded that what we typically call fully cured is not where the process really stops and full curing activity can be occurring many days after an epoxy has acheived the majority (90%+) of its ultimate strength and is hard to the point of being non-dentable, though clearly at a very reduced rate. for those of you who have built and held epoxy boats for a long time, think 'print-through' and how long that takes to show up.
based on my read, my sense is that the differences in observations of 'tackiness' are probably due to variations across a number of factors including 1) how agressive and how much time the wipe down is, 2) temperature and other factors that effect the evaporation rate of alcohol, 3) variations in formulations of various denatured alcohol product, 4) where along the 'cured' continuum the underlying epoxy is and 5) how sensitive is one to determine that something is actually 'tacky'
my tune after all of this is as psimian says and chester's experiments point out, you definitely don't want to do an extended passage on a epoxy coated boat on a sea of denatured alcohol. save that for your plastic craft.
I don't think the alcohol is doing the slightest harm to the epoxy when used as a pre-paint or pre-epoxying wipe down. In fact, I wouldn't be surprised if it helped to promote a better chemical bond between the coats of epoxy, but am only guessing. I only posted about my observation because others were skeptical of the OP's experience when I had the same thing happen to me.
If you google denatured alcohol you get a list of all the denaturing additives and there are a lot of solvents among them. I suppose a MSDS (Material Safety Data Sheet) would have the contents, if not the proportions. Alcohol may not be the only active ingredient at work here....
Hey Chester Yall..for some reason I can only post from my phone and need to talk to you about this topic...could you please call me..830/997-8120...thanks!