Need help for the first course

[tutti_frutti]

Hi guys,

Today i'm starting my oven dome

I am laying my first course on the paste made out of clay and sand (1:1), just like the paste my floor is laying on.
Can i also use this pase to fill the gaps that i have between my first course and the oven floor? Or should i use refractory mortar? or nothing and leave the gap?

Thank you in advance for your answers

[UtahBeehiver]

Leave gap, it is an expansion joint, will fill in with ash later. Be sure to cover gap when building dome so mortar does not get in or drop down the gap. Some builders reported cracking because the mortar caused stress on the floor since it had no where to move as it expanded during fire up. PS a good rule of thumb is a gap about the thickness of corrugated cardboard.