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The 2018 FHB House is a net-zero energy, high-performance home in California’s Sierra Nevada foothills designed to meet the goals of the California 2020 initiative and comply with the most progressive energy code in the country. The project combines a very tight, well-insulated envelope, cutting-edge mechanical systems, and unique material choices, all wrapped up in a one-of-a-kind modern design.

California 2018

Tools & Materials

Breaking Apart the Toughest Rocks

Our strategy: A rock drill and Dexpan.

By David Good
Article Image

We had seen Dexpan used before. It is a mysterious powder that you mix into a batter and pour into a borehole in the rock. The mystery is how it can expand when it dries and how it can dry in a deep confined space, thus fracturing the rock.

Clyde had acquired a CP22 rock drill from an old miner friend but had not ever used it. He also has a large diesel compressor to run it. I ordered some drill steel and diamond bits and we got to drilling. Simply lay out a 12-in. grid where you want to cleave the granite, bore the holes, mix the Dexpan, fill holes, and wait 24 hours for the magic.

With a rock drill Dave prepares holes for the Dexpan

We had perfect results with the Shark’s Tooth and mixed results with the Thermal Bridge. The prescribed 24-hour dry time was too short for us but luckily by 36 hours we had good cracks. The Thermal Bridge probably could have been moved with the CAT 330 but we forgot about it after draining ourselves on the Shark’s Tooth and Basement Boulder last week. The fractures in the Thermal Bridge provided an escape route for the Dexpan pressure in some of the bore holes and the shape of the fractures formed a gravity trap that held it tight. It would not break apart as we had hoped.

A nice clean break here on the Shark’s Tooth after the Dexpan dried and expanded enough to fracture the rock.

 

After it’s been split you can see the dried Dexpan in the bore hole.

My foreman Todd hammered some steel wedges and finally developed the fractures enough to ‘break’ the Thermal Bridge! Now there is room for the continuous Rockwool insulation under the basement slab.

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California 2018 Videos Behind the Build: Rhode Island 2016 Behind the Build: Vermont 2017 Behind the Build: Kentucky 2019 Behind the Build: Connecticut 2020

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View Comments

  1. CT_Yankee | Jul 26, 2018 05:20pm | #1

    "Thermal Bridge", Shark’s Tooth", and "Basement Boulder" . It's nice that y'all tagged the rocks with nicknames, although it does nothing for those of us unfamiliar with the excavation.

    "Dexpan" is a trade name for a non-explosive demolition agent, as are "ECOBUST", "BETONAMIT", "Bustar", "THE CRACKER", "Bristar", etc.

    All they are is an expansive grout (probably containing a high amount of gypsum). Most "non-shrink" grouts exhibit limited expansion as they begin to cure and then shrink back to the original volume as the cure completes.

  2. ptygmatic | Aug 18, 2018 02:05pm | #2

    Very Cool! Rock mechanics in action!

  3. User avater
    DianeCPfarr | Oct 29, 2018 03:35am | #3

    Good job you are doing here!

  4. User avater
    devinkoblas | May 07, 2019 03:03am | #4

    Good Job!

  5. User avater
    JohnPrice6 | Jun 11, 2019 07:51am | #5

    It's too good!

  6. User avater
    ArmandLewis | Jul 03, 2019 06:23am | #6

    Nice job!

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