I received this question in episode 6 of the Ask Brian Boggs Show:
How do you protect the mating surfaces of a glue joint from a finish that you are applying prior to glue-up?
I mostly use a very slow-drying, Tried-and-True, old-fashioned linseed oil for finish, and Titebond 2 for glue. “Tried-and-true” is a little bit of an issue in this. It’s just pure linseed oil, and I have used it before. It tends to wick across and into the wood more than some other oil finishes. I’ve had better luck with General Finishes, the ArmorSeal that we use, and we use a Seal-a-Cell as a sealer. They are chemical … there’s a lot of toxins in there, so if you really want to stay away from that you can continue to use the Tried-and-True, but you’re not gonna be able to get all the way up to a glue service, if you’ve got a tenon for example that’s flush with the outside of the piece. You’re not gonna be able to glue up to that and not have some of that tried-and-true creep into that. It’s designed to penetrate wood, and that’s what it does. And so it wants to creep along any scratches or any pores along the way, and it will get up on the glue area.
Even masking those joints will not help you. In fact, I would strongly advise against masking, because masking tape can leave a residue that can interfere with the bonding. Not quite as much, maybe, as oil itself, but I would stay away from that. One of the things that I know people have done when they’re going to use an oil finish, and tried-and-true would cooperate with this, is you can just use a wax, a furniture wax, right around those joint areas. Furniture wax is not gonna creep, it’s gonna hold really still. It’s a paste, it’s gonna sit right there and allow you to pop that glue right off or clean that glue off easily. Then when you rub in the oil later, it’ll blend with that wax and mix up with it, and it’s just not likely to be a problem.
Tried-and-true … if you’re using that much, you probably know it’s really not much of a protective finish. It’s a very open finish. It will color the wood nicely, but it will hold dirt. It’s not easy to clean, and while it will (in theory) dry eventually, it’s not your best finish from the standpoint of durability and protection. There’s a whole lot of economical and environmental reasons to use that, so if that’s the one you want to stick with, I would either just plan on spending a lot of time washing glue off or wax those areas rather than oiling them.