I suppose the comments re stabilization and Cactus Juice have a lot of credibility but the cost is something I considered and found the Minwax hardener to be a very cost effective and functional product. Typically I rough turn any punky wood to about 1/8"-1/4" of desired finished product. Paint it on, allowing it to soak in and when it leaves a shiny surface, I re-turn and have been very happy with the final result. I use cheap disposable brushes. Stinky yes, but then so are many finishes we use. Use appropriate protection. My only negative comment has to do with sanding, and it probably is a reflection of my less than ideal sanding technique. Easy to burn with sandpaper. Easy fix; go slower. I have a great looking piece of pretty rotten BLM burl waiting for final finish (otherwise I would add pic) and the final cuts and sanding give no suggestion of soft, rotten wood but the grain is fantastic. Also I see no indication in the final finish in other pieces of finish problems using shellac, WOP, lacquer or WTF.
Minwax Wood Hardener review. *****