Is that top the hearth where your fire bricks or tiles get laid or are you sitting a whole new hearth on top? I am only asking because my top was almost black when it cured but I used a brand of refractory cement called La Farge.I then laid firebricks on their narrow side on a bed of sand & fire clay. Would do tile next time.I know I already said this but Man your contracter is neat.
We just finished a layer of fire bricks and are discussing with the manufacturer about a second layer. We want to bake bread too and I have read that the second layer of firebrick gives you a lot better heat control on the floor of the oven and for $60 that is cheap insurance. I will post the next pics in a few minutes