Sap leaking from a new shelf - varnish or wait

Generalissimo

Hopefully this question's in the right place

Some friends of mine are in the process of finishing off their new house. They have a long shelf (which they think is made of sycamore) that they're planning to put between the divide between the kitchen and dining areas. There had been sap leaking from the shelf so they waited until it stopped leaking before taking it outside and giving it the first coat of varnish. The sap has been running mad since. My friend is wondering is that from the warmth from being out in the sun or is it because of the varnish? If it is the warmth would they be better off waiting until the summer before finalising the shelf or is there something they could be doing now so they can get the shelf finished and in place?

Many thanks for any comments/suggestions.

jack of all

Best thing to do is try and scrape off as much of the resin as possible and give it a good wipe with white spirit and a rag. Then treat with a shellac knotting solution before going at it again with the varnish. Shellac knotting is alcohol based and won't disturb or dissolve the resin which then bleeds through a finish. White spirit based finishes won't hold up to resin seeping through, so shellac knotting first and then varnish or paint.

Generalissimo

Thanks, that's a great help - I'll be sure to pass that on to my friends.