I'm making a live edge table top out of two pretty "rustic" walnut planks with some cracks and voids. I am planing on filling them with clear epoxy. One of the voids is pretty large and has some soft slightly rotted wood and some with carpenter ant holes along one edge. Do I need to remove all of the soft material, or will the epoxy penetrate it a little bit and harden it? I would like to leave it in if possible since it adds to the rustic look. I would post a picture if I could figure out how.
I wouldn't count on standard epoxy penetrating the punky wood very far. However there are some super thin epoxies just for that purpose. Check with Jamestown Distributing.
As for filling a large void, you may need a special epoxy for that too. Most will generate enough heat to boil if the hole is too large.
I have been thinking about Epoxy and tables for a while. Trying to get an answer about how long they hold up. It seems to me the epoxy and wood would have differing responses to changes in moisture content and temperature and that over time the wood would "squirm" loose from the epoxy. I also wonder if the epoxy would not get dull, scratched and hazy over time and need re-polishing. I have asked several purveyors of river tables about this and get no answer.
As for your punky wood I seriously doubt you should leave it without hardening it first. I wonder about the chemistry of mixing Minwax Wood hardener and epoxy. I would do a test with the water thin version of epoxy and the filler epoxy.
On youTube check out Canadian Woodworks. Been watching their blog and they make a lot of such tables and seem forth coming with ideas and supply's. They sell custom made C channels for the underside and the inserts to put into the wood to bolt in the channels. They also sell Chill Epoxy that is suitable for deep pours. Matthew Cremona has also done some large pours using buckets full of epoxy with success. (He also has an interesting sawmill he built himself)
There are lots of other people on youtube doing similar work. Check it out carefully, the epoxy gets pretty expensive. Too costly to create some sort of poorly thought out blunder.
The hard maple "river" top I did and wrote up here was attached to the cabinet such that the 2 halves could expand and contract as a unit so the epoxy-filled center can move with them in unison and stay tight and bonded to the wood. The cross-joint dominos no doubt help on this issue as well.
Conversely, if your design and build pits the wood against the plastic, something's gonna give, namely the epoxy/wood interface.
If I recall correctly, the Minwax wood hardener wants you to essentially remove the soft, rotted wood as much as possible. I don't know how much penetration it gives you and it may only go in a small distance, leaving a soft core that isn't hardened. You might want to experiment on a scrap piece and let us know your findings.