MTO Firebrick Arch entry

Posted by Evert

Good day Rado! I tried to follow the MTO pictures but with my provisional test-arrangement have ended up with an entry to vault ratio of nearly 70%. I used 35mm firebricks at the front, started at the 203mm (8") level on the sides but ended up 276 (10.9")mm at the centre of the arch.

Now I know the difference to your photos is only at the centre of the arch (mine curves higher), but what would you suggest I do:

1) slot in underneath another arch(approx 20mm deep below the current arch) cutting in the sides to correct the percentage;
or 2) will it be OK with not too much temperature loss as the difference is only on the top centre 20%.

To remove this arch altogether would be very difficult as I have already encased the hearth with concrete cladding.