Mortar and Foundation for Bottom Of Hearth Addition

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New Member
Feb 16, 2024
Washington DC Metro
Hi, I have a floating flagstone hearth on my fireplace from the 1950s. I recently had the top of my brick chimney rebuilt with new brick, and decided I want to use the original brick to build a foundation under the floating hearth (so it will no loner be floating) for a more classic look. It will take 3 courses from the floor to the bottom of the flagstone hearth. I have two questions:

How do I match the color of the mortar on the new part to the mortar of the existing brick on my fireplace? The existing mortar is very light in color (see photo) as opposed to the very grey looking mortar I typically people using now.

Also, I want to leave the wood floor in tact underneath. What should I set the bricks on? I'm thinking I would install quarter round to it instead of the floor so maybe plywood or cement board? I read that plywood will soak all the water from the mortar and not to do it, but I don't see a need for mortar under the first course of bricks. Thoughts?? I was also thinking maybe cement board or plywood with some roofing felt underneath or something to preserve the floor just in case. I probably will leave this brick in place, but don't want to destroy the floor just in case I ever want to remove it for the original look.


I'm thinking of filling in the bottom under the hearth like this:

The One.jpg