ACL Project List
 

Treatments were divided into two major categories: those addressing the structural support of the tile, and those addressing the terrazzo surface – the design layer with its insets.

 

Extraction
When originally installed, each tile was framed and locked to its contiguous neighboring tiles. As a result, any given tile could only be dislodged by sliding it out from its neighbors. As such, the tiles along the edge of the Pavilion had to be removed first. Since the plain grey tiles could easily be replicated and did not contain any map imagery, several of these were sacrificed to make room for the map tiles to be slid out of place. The first step was to carefully separate the map tiles from the under bed as well as from one another and then insert a specially designed “rake” that was used to pull the tile out onto a ¾” plywood board.

   
 

Facing
Once the tiles were separated, they were faced to hold all loose fragments in place and prevent further damage to the terrazzo during crating and transfer off site. “Facing” is a technique that involves adhering paper or fabric to a surface with a reversible adhesive for protection or support. 14 inch squares of cotton gauze were adhered to the tile using methylcellulose. The squares were slightly overlapped until the entire face was covered. The retention of soil and debris infilling areas of loss was beneficial in stabilizing the highly fragmented tiles during removal and could be removed later during treatment. To contain the tiles 2”x 6” wooden sides were attached to the ¾” plywood board base and a cover was added.

 

Once in the lab the tiles needed to first be inverted. Each terrazzo tile weighed approximately 400 pounds requiring only 4 people to turn over and place on the table. The structural integrity of each tile had been compromised. In situ, many tiles had developed a concave deformation as a result of the decay of the original plywood substrate. The facings were used to hold all the fragments in place and the flexibility of that fabric allowed the irregular terrazzo top surface to be pressed flat once it was turned over.

 

Structural Repair and Cleaning

Roots and soil embedded in the tile were removed by hand with brushes and a microspatula. In some cases, the soil was all that was binding the terrazzo and substrate in place. An effort was made to retain as much of the original fabric as possible, particularly portions that contributed to the design and integrity of the tile. However, there were sections of terrazzo and substrate that were too heavily disaggregated and damaged to be retained.

 
 

The original wood support had completely decomposed with the exception of a few small detached fragments. Once flipped, it quickly became apparent that most of the cementitious substrate was crumbling and detached from the terrazzo that it was intended to support. It was decided to remove any of this substrate along with structural rebar that was not well adhered to the terrazzo. The substrate was removed by hand or a metal putty knife assisting in prying up fragments that were lodged in place. Most of the rebar was very close to the surface of the substrate allowing for their easy removal.

 

The replacement substrate would fill in any loss on the back of the tile but in order to ensure that the terrazzo fills on the front would have enough depth and proper edges for the new infill material, Plasticine clay and silicone caulk were used to build up these areas from the back side. This material could later be removed to allow for fills on the front. Before the structural pour a framework was placed around the perimeter of the tile to contain the new substrate and create an even 4’ x 4’ square. With the clay/silicone in place, a liquid bonding agent was brushed onto the entire tile back and into the cracks to assist in bonding the new substrate to the original terrazzo. To ensure a good bond and consolidate the heavily cracked surface, a thin slurry coat of cementitious floor leveler was then brushed on, penetrating all cracks and fissures before the structural pour. Next a thin layer of floor leveler was poured up to the level of the original substrate. Once the tile had cured for at least 72 hours a 4’ X 4’ Phenolic honeycomb was adhered to the new substrate with an epoxy resin adhesive. Once fully set, the tile was inverted so that it was face up again.

 
Surface Repair and Cleaning

The first step was to remove the surface dirt. A solution was scrubbed into the surface for 2-3 minutes and then flushed with water. After the entire surface was cleaned and left to dry, Heavy Duty Concrete Cleaner was used to remove more stubborn stains and the white carbonate laitance that had formed through weathering, particularly on the red terrazzo. A wet/dry vacuum was always used to pick up the rinse water to prevent excessive moisture from penetrating the cracks. In some areas where the stains and laitance persisted, an additional application of the cleaner was used.


Loose original insets were reattached using epoxy putty placing place them at the level of the surrounding terrazzo. Insets that were heavily damaged or missing from the tiles were replaced with new Plexiglas insets in black, red, or green. The shapes of each element were drawn in AutoCAD by tracing insets from photographs of the tiles and using a scanned 1960 Texaco Road map recreating the missing shapes and letters.


Fills were made using pigmented Mortar. Areas of loss were filled to the level of the surrounding terrazzo, but were slightly recessed to indicate the repair. The application procedure included pre-wetting the substrate and applying a rough leveling coat of untinted mortar, followed by the tinted mortar, which was raised above the terrazzo and then shaved down using a palette knife. A natural sponge was used to compact the mortar, expose the aggregate, and remove any excess water.