I recently assembled a shed and one or two of the board on the wall are "leaking" sap:
I thought it might stop after I removed the first batch but a few days later, it came back. Is there anything I can do to stop this (while still preserving the natural wood look)?
I've already put three coats of polyurethane over the whole interior.
It's a pitch pocket.
Just give it time - "a few days" is not much time in this case - it might ooze for a year before it gets done. You could try heating it (to make it ooze out faster), but that might have detrimental effects such as checking, a.k.a. cracking; or in this case, cracking more.
I agree. It will eventually stop. This may sound extreme, but since it's localized around the knot couldn't you use a small mortise-type drill bit (the type that leaves a flat bottomed hole) to remove the offending sap knot and then fill with putty?
