Masonary Help: How do I finish the Chimney top? (bridging a 2" airgap around 12"x12" flue?)

Hi -

I'm slowly getting the brick and mortar chimney extension completed. I've got a 25" outside dimension square of brick with the 12"x12" flue tile in the middle. This leaves a 2"air gap around the sides. Any suggestions on how to bridge this gap when I form the cap at the top?

It is coming along. Next week is liner time.

Ordered a Dolmar PS5100S saw... The old Mac's will be limbers now.

Thanks in advanse.

Mike P (who is not a mason)

many use alumium flashing in the last course of bricks to fillin the space before pouring in the cap.
spme make a form out of 2/4 or strapping out side. If you want a 1.5" overhang then space it witha 4/4 even with
the top brick and add more wood 2.5" up what ever height so desired

Domlar is now owned by Makita quality tools quality saw good luck with it