Because the outside walls of the wood box's barrel vaults are not buttressed, the immediate space above the barrels will be reinforced with concrete and steel. This will eliminate outward thrust and convert all the individual elements of the vault into a solid unit able to withstand both compression and tension.
At this stage, concrete has been poured over the barrel of the arch and pieces of #4 rebar have been fitted to the radius of the barrel and placed on 4" centers within the concrete.
Concrete is then poured again, and pieces of #4 rebar have been placed laterally on 4" centers within the concrete. A grid was later established by placing rebars in the opposite direction.
On the other side of the fireplace, the second barrel vault form has been set in place and is ready to receive masonry.
Second barrel vault completed.