Glad I could help.
As far as the hot water, that may or may not work. It depends on what kind of glue was used. If it's a natural glue, like they use to make from boiling up hooves and things, then yes. Drop the whole thing in boiling water for 20 minutes, and you'll be able to pull the bristles out very easily by hand.
If it doesn't work, it shouldn't do any harm.
The brush I restored was a rubber set brush, so that didn't work. instead, I grasped small clumps of bristles near the handle with needle-nose pliers, and rolled the pliers. Not twisted, but rolled. At first the bristles just broke off, but after a few tries, I started getting clumps, and the clumps got bigger and bigger until I was pulling the rest out by hand.
As far as gluing in the new knot, that's the easiest part of the whole process.
Pretty much any kind of glue will work, but ideally you want something that will set with little to no exposure to the air, and something relatively waterproof, so ideally we're talking about a 2-part epoxy.
Loc-tight makes a whole line of very inexpensive 2-part epoxies that you can get at virtually any hardware store. I like their orange epoxy. (they label and sell their epoxies with color names, and in color coded packages to make life easy if you didn't know)
I like the orange for several reasons.
- it sets fairly quickly, but slowly enough that you have time to work and clean up.
- it's sets clear so you don't have as much to worry about in terms of a mess.
- If you do make a mess, it cleans up VERY easily with denatured alcohol as long as you get to it before it sets. (keep some alcohol and cotton swabs handy)
I can give you a couple other tips about the gluing process.
- it's easier to glue the knot in if you get a knot that is just slightly smaller than the hole. The site I linked sells in metric sizes, so you may have to do some conversion unless you have a metric ruler. The sizes refer to the glue plug that the bristles come set in. Just measure the hole in the handle, and round down to the next millimeter, or deduct one millimeter.
- Mix the epoxy on a piece of tin foil or something else you can throw away, and then spoon it into the handle. If you try to mix it in the handle, you may not get good adhesion.
- Once the epoxy is in there, it will be tough to push the knot in, because the epoxy will be thick, and won't want to squeeze up the sides where you need it. If you twist the knot as you put it in, it will go much easier.
- Test fit the knot about 10 times because once that epoxy goes in, you're committed. The outside of the knot, where it's glued together, can be sanded a little if you don't feel there's enough room for the epoxy.
- The glue on the end of the knot should be sanded lightly regardless, and the inside of the handle should be cleaned with alcohol or acetone and sanded as well.
- If too much epoxy squeezes out, don't freak. Freaking out will just make a mess. Just grab the denatured alcohol and q-tips and clean it up. You'll have 5-20 minutes to clean it which is plenty of time. Other solvents may work, and other epoxies may require different solvents, but I can tell you from experience that denatured alcohol works perfectly on loc-tight orange.
I'm sure I've gone from making this sound easy, to making it sound complicated and scary, but it's really not. I can post pictures of the brush I restored if you're interested.