Suspended Stone

We live with the assumption that anything stone or brick should be directly connected to the ground. In class this week we proved that doesn’t have to be true. In Traits & Form with Benjamin Ibarra Sevilla, we built an irregular elliptical vault at one-fourth scale to the original Rafeal Guastavino vault in the Municipal Building, NY.

Marcus and Peter preparing for our second day

We used similar materials to Guastavino’s methods: plaster and thin ceramic brick. Typically in arch or vault masonry, the structure relies completely on compressive forces of the form acting as one. When building these traditional arches it is necessary to have framework holding every stone in place until the keystone is in place and the individual stones work together as a complete form.

With Guastavino’s method, the bricks are so thin and the mortar is strong and quick-setting. Each tile can be placed with mortar holding it to the previous tile and it will just stay there. It could be thought of as quick-set concrete with really large aggregate.

Incomplete Arch, aka: cantilevered Tile

Before actually building this vault, I couldn’t imagine placing a tile without it falling to the ground immediately.  We started slowly in the corners of the vault, where the tiles were still only tilted slightly and wedged between two former-arches. Then we reached the point where the ellipse was practically horizontal and we were placing full-sized tiles with just plaster on two sides, place it, tapped it, and held it until it stayed. It worked! The plaster set quickly enough that we only had to hold some in place for 5-15 seconds and they would stay.

The tiles are not even relying on the formwork we had in place, it was more of a guide to keep the directrix straight.

It got to the point where we were almost too confident and instead of building up both sides of an arch, we were just reaching across from one side. This meant that we were placing tiles that were only connected to the vault on the two sides away from the ground. These were completely suspended and staying in place! It felt like we were doing what this artist has done with suspended stone.

It was a very successful project and we will be letting it stay up all winter. In the Spring we will test to see what it takes to knock it down. To see the video of all of us climbing onto the vault to test its structural capabilities, please see the following link:


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