I took down all the casings in a kitchen (6 doors and a window), had them stripped, and reinstalled them before repainting. Since the house had settled quite a bit in the ~80 years they were in place, the miter joints are all off, hidden by paint previously. My first idea is to Bondo them, or use setting type joint compound to fill the gaps. But other similar casings I've done in years past often show a crack in the paint at the miter, apparently due to seasonal changes. Is this a good place to use painter's caulk? I'm reluctant to use something I can't sand flat, and might bulge out or dip in.
(Architectural Woodworking Forum)
From contributor J:
A lot of the finger-jointed casings in our house were caulked, so I continued that trend when I started remodeling. I found that cheap painter's caulk and adhesive caulk would shrink upon curing, requiring a second pass to get ideal results. Higher grade siliconized latex caulk (like most 50 year exterior grade caulk) shrinks less, but still shrinks. I've tried Bondo - too much odor for staying in the house; had to evacuate for a day. I've tried putty, spackle and plaster type mixes - easy to tool, don't shrink much (spackle does a little), and is great for nail/brad holes, but wouldn't recommend for mitered corners or anywhere that seasonal humidity changes will cause the joint to move.
Overall, I typically go with a cheap latex painter's caulk. The technique I use for inside corners is to cut the tip with a slanted 90 degree chisel point, so that when the tube is at an angle of 45 degrees, the tip is totally flush with the inside corner. Then, knock off as much of the pointy tip (which is the trailing edge when you draw the bead) to give the size of bead you want - usually about 1/16". Drawing a damp finger is always best to give the caulk good contact and smooth finish. For nail holes and mitered joints that you want flush with the wood surface, I apply from the fingertip, and use a putty knife to smooth it across the grain (to follow the molding profile). By applying a little surplus, then drawing the knife in only one direction, you can usually leave the caulk a little bit high only over the holes - takes practice. It will cure to almost flush.
If in doubt, put on a little more, let it cure, then come back in two days to trim the excess across the grain with a chisel - that's why I use cheap caulk, easier to trim when dry.
Contributor R, that's a good idea in theory, but the job isn't the whole house, just the kitchen, so I only took casings off one side of the doorframe. I've also learned the hard way to keep dismemberment of 100 year old places to a minimum - you never know what can of worms you'll open with what seemed an easy fix. Chipping a little paint turns into a disaster when the paint is all that's holding the decayed plaster together! Yeah, the wall should be repaired, but it isn't what the customer signed on for.