What type of caulk or sealant should I use to fill a space on my fireplace hearth between the slate & the wood frame that surrounds it. The hardwood floor was refinished, but the wood framing around the fireplace hearth needed to be replaced. Afterwards, there was a gap between the new oak wood frame and the slate hearth. The hearth seems to have some kind of concrete or bonding material holding the slate pieces together.
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:
How about replacing the strips of hardwood you removed? This is an easy project for any finishing carpenter and most general handymen.
You could either try to match the rest of the flooring—which isn't that hard. Or us a dark wood, maybe dark stained wood for some contrast.