Help with bricks please

[Chubbychaser]

Hi all,

Currently embarking on building the dome. Floor is firebrick but due high cost of firebrick in uk I plan on using a Cheshire pre war Common brick for the dome. They are a little uneven on the edges and although the brick is fairly uniform inside it does have some small 'bits' in it, so I am a little worried about spalling after reading nightmarish stories on forums. I have around 25 half firebricks left so was wondering about using these for the top few courses of the dome (seems a shame to waste them and I dont fancy spending days crushing them.) has anyone any thoughts about mixing and matching different bricks for the dome in this way or any thoughts on the spalling? Half brick photo attached.

Any advice much appreciated. Thanks in Advance

[Toomulla]

Any well fired brick will probably outlast a you, having said that, as the most intense heat is the top of the dome I cannot see any reason not to use what toy have for the top courses