Protecting "tree trunk" slab tables

I have two chunks of maple that came from a tree that have been squared off. They've been indoors for many years and were lovely but now we'd like to use them outside as tables for a patio. As they are extremely heavy, (200-300lbs each) we've been lazy about sanding and sealing them with spar varnish. Now with a wet Spring, a weird white/blue mold is forming and we are going to take them back indoors to dry out. The question is, certain parts that had been damaged/cracked in the past have become a little spongey in the elements, clearly the early stages of rotting. If they dry out for a month or so, would it be cool to just spar varnish over the spongey parts, or do I need to chisel those out?

 

That wood is not in good condition. I would rub on several, very liberal coats of linseed oil and use the tables. The nice thing about linseed oil is you can apply more coats anytime you wish.