About 18 months ago I made a mail box from some old silky oak. The timber looked to good to paint over so I decided to finish it with marine varnish. The sides are still in excellent condition but the top has crystallised, hard loose and flakey. The finish used was Feast watsons Spar Varnish. It can't be wet weather because rain is a naughty 4 letter word here.As I am about to try and get it looking good again can I ask what has gone wrong and what would you suggest as a finish? vinnie