Hello, I had a joiner in to fix a sill with rot and asked what I should use to seal the vertical wooden frame to the masonry which looks very messy and has holes in. He said use decorators caulk and paint over. He used caulk to seal the sill to the window ledge. But when this came up in B&Q they said no way, caulk is for internal use only and won't resist frost even if painted. They said use silicone frame sealant instead. So I thought to ask people who'd done it themselves: who is right? This is for 4th storey window facing south in Scotland that get a lot of rain and weather wear. Also, should I remove the existing sealant on the verticals which is in a mess or just seal over the holes? I am a total novice at all things diy...