How do I fill a gap between my hearth and the hardwood frame around it?
Buy a small bag of concrete floor patch: it mixes like pancake batter and sets a light gray. This is what you fill that gap with. It gets hard as concrete and will adhere to the existing stone. If you don't want it to stick to the wood then mask off the wood before. It also helps to protect the top of the wood with masking tape. If you need more of a curb effect form at the edge of the hardwood with the propped height wood strip and remove when patch is dry. I have a picture of something like it: