Scenario: Had to remove baseboards, window, and door mouldings to take hideous panelling off the wall.
What’s the best way to put the moulding back on? If I use the same nail holes they’ll match the holes in the sheetrock and it won’t hold. Do I make new nail holes and use colored putty in the old holes?
That would be the approach I would take.
In fact, if you have a LOT of molding, I highly recommend an electric nail gun. They look like a staple gun, but fire little brads (nails). It makes the whole thing go a lot faster. You can get these in the local Home Depot next to the staple guns.
Your other option is to rent a small (called pancake) compressor and a finish nail or brad pneumatic nail gun. Compare the pricing of rental versus purchase.
As you remove them. make note on the backside where they go when you’re ready to re-install. (you’ll thank me).
I actually did this and as well as making little map! It was a fortunate “lightbulb going on over my head” moment.
I can’t afford a nail gun at the moment. Do I use the “headless” nails and a nailsetter to get them in a little below the surface?
Yes. Finish/Finishing nails. Take one of the old nails in with you when you by them. I suspect you will want 6 penny nails. And maybe some 4’s. Nails are cheep. Get a couple of different lengths. You can also buy tiny little jars of pre-colored wood putty to smear in the nail holes. So, also take in a small piece of molding if you can to try to match the color.
In the trade we use #6 finishing nails for standard baseboard and door casing. Sometimes #4’s if we need to tighten up the “inside” (the thinner edge) part of the door trim.
When driving nails by hand it’s easy to split the end of a piece, depending on the material. If it’s really nice stain grade stuff, we will sometimes drill a pilot hole at each end of the piece, or you can do the old the old trick of whacking the pointed end of the nail a few times to blunt it, just don’t bend the nail.
To do it right, drive the nails almost flush with the wood and use a nail set to sink them into the material. This prevents hammer marks and gives you a small hole for the putty.
Also, you don’t want to nail just into sheetrock, but into the framing material behind the rock. Try driving a nail partway through one of the old holes, if the carpenters who originally installed it weren’t idiots, you should hit solid wood, then just space the nails a bit away from the old holes.
Probably more than you wanted to know, but if you have nice material, it would be a shame to mess it up reinstalling it.
I would really look into renting or borrowing a nail gun and pancake compressor. This will save you tons of time, and if you aren’t perfect with a hammer you might end up dinging up the wood with regular nails. I’m thinking that when we rented a roofing nailer (which is quite a bit more expensive than a finishing nailer) it was about $20 a day. We already had the compressor, so I don’t know how much that would be, but I would think you could probably get both for about $50. It will save you sooooo much time, really.
Klaatu knows of what he speaks. Unless using a nail gun, you probably want to predrill all holes to prevent splitting. It may sound like a pain in the butt to do, but it is much better than trying to piece in new wood to match the old because you have split the trim. If using a nail gun, try it out on some scrap wood, to get a feel for the gun, how to use it, and to set the depth of the nail. Glad you figured out to mark the pieces, you simplified your life. If the moulding was resting on the panelling, you may have discrepencies in your mitres now. Just have to start nailing it on to see.
Thanks for all the great advice. The hot water heater just broke, so there go my dreams of renting a compressor for this job 
I’m going to try drilling pilot holes and using a setter. Ah, the joys of home ownership!
Sorry about your water heater. If we lived in your area I would lend you our compressor and gun, but I doubt you are in Japan. If you posted your location someone might take pity on you and let you borrow theirs. They are pretty idiot-proof, you wouldn’t be likely to damage the equipment (watch those fingers, though).