Becker’s Blog #10: Floor It!
The existing cathedral floor was one large pattern of 12” X 12” X 1” Mankato limestone quarried 200 miles from the church. The limestone was installed in a fresh mud bed and bonded/adhered to the concrete slab floor with Portland cement.
From what we’ve seen in old buildings, the mud bed was always bonded to the concrete slab. They didn’t use isolation membranes as we do now; because of this, a crack in the concrete slab often transferred up through the mud bed and cracked the stone paver. The concrete floor, mud bed and stone moved as one.
Sioux Falls Construction began the demolition of the old limestone pavers and found a good bond. The jackhammers made the inside of St. Joseph Cathedral one of the noisiest and dustiest places in eastern South Dakota for three weeks. With the limestone removed and the dust settled, what was left was a rough floor with high and low areas that varied up to 1 1/2”, which wasn’t what we expected to inherit as a working surface.
In bidding the project, we priced the installation using the TCNA F-111 specification, which has the stone and mud bed isolated from the concrete floor with a cleavage membrane. In our case, we would use tar paper as the membrane.
The theory behind F-111 is that if the floor slab would move or crack, the membrane left a separation that would stop the crack from transferring to the stone. The floor slab and stone can move independently from each other.
However, the rough floor of St. Joseph’s created a problem on several levels. First, there was no way we could work over the floor as moving 2,500-lbs crates with pallet jacks would be impossible.
Second, there would be thousands of air pockets below the tar paper, as it wouldn’t completely conform to fit the rough slab. Air pockets are bad news in a stone floor, as they create hollow sounds when walked upon. Hollow sounds are bad news for the stone contractor. (The sounds do happen from time-to-time, even on the best-laid floors, but that’s a whole separate discussion.)
With a rough floor in front of us, we worked with the people from Custom Building Products to find a solution.