When I first built my wood fired brick oven, it took an age to get the floor dry. There is vermiculite based concrete under the bricks as an insulating layer, and it's a slow process getting the water out.
Naturally, while this was happening the undersides of the pizza were not cooking well at all.
So I used a 3/4 thick slice of natural sandstone on top for the first 1/2 dozen pizza nights.
Pt worked great.
I cannot see any reason that the opposite wouldn't work. You should be able to put a biscotto stone on a deck to reduce heat transfer to the bottom of the pizza.
