The Learning Process
Ed Crocker evaluating a test panel
There are very few people still alive who have expertise in building and maintaining stone-slab buildings.
The challenge for this restoration was to reverse-engineer the techniques used by the Hutmachers.
The next challenge was to modify these techniques to reduce the maintenance cycle while keeping the buildings authentic.
To help in this effort, Preservation North Dakota turned to Edward Crocker. Mr. Crocker is president of Crocker LTD, specializing in restoration of earthen structures.
While Mr. Crocker came to the Hutmacher project with considerable knowledge of earthen structures, the Hutmacher presented some unique challenges. Mr. Crocker’s experience was primarily in the southwestern United States, a warmer and dryer climate than western North Dakota. He was also limited to materials that would have been available to the Hutmachers.
The east wall of the Granary was used as a test section for the mud mortar used in the walls. The original mixture was analyzed and three alternative mixtures were developed and applied to test sections on the wall. After a winter of weathering, the sections were examined and the most durable “recipe” was selected.
The clay mixture used by the Hutmachers was modified to include autoclave lime and a controlled mixture of different sizes of angular aggregate. The native aggregate clinker, commonly referred to as scoria, was used for the mix. Scoria consists of clay, silt, and sandstone naturally baked or fused by the heat generated from the burning of underlying lignite coal.
While the new mix was a great deal more durable that the original recipe used by the Hutmachers, the scoria mortar had a more reddish color. To retain the original look of the buildings, it was decided that the final exterior rendering coat would have little of the scoria in the mixture.
The Learning Process
