Saturday, 8 August 2015

Forming Rammed Earth Walls (Wall A)

Welcome to the latest update about building "The Cabin in the Woods".  We are underway forming the first rammed earth wall (Wall A).  It is almost 24 feet long and turns 90 degrees.  There is some forming complexity as it also has two window "knockouts".  Knockouts are spaces in the rammed earth wall for windows to be installed later.
Wall A looking east from the interior of the building.  
Wall A looking north from the interior of the building.
I had a team of surveyors visit the site and locate the corners of the walls in relation to each other. The layout of the Cabin in the Woods is not an easy one and to do this using my rudimentary layout tools would be laborious and inaccurate by comparison.  The surveyors are able to create points they can locate to within 1/8" (3mm).  At every corner the surveyors insert a metal spike into the footing. We are using these spikes to locate our wall corners.

Surveyors spike in the footing tells us within 1/8" (3mm) where the corner should be.
Nothing in this world is perfect and so tolerances need to be considered when forming a wall.  An acceptable flatness variation in our wall is going to be 1/8" over 10 feet.  That means that a ten foot straight edge should remain in contact with the walls surface or (as a maximum) come 1/8" (3mm) off of the wall in any direction.  We avoid accumulating error by using the surveyors corner locations as our guide and not assuming that our constructed rammed earth walls are accurate enough to measure from.  For instance, if a wall reaches its maximum flatness tolerance error of 1/8" (3mm) and we measure from that wall to build our next wall it too could reach a maximum permissible error of 1/8"(3mm) creating an accumulated error (total error) of 1/4" (6mm).  In order to create a flat wall, our form work needs to be rigid enough to resist the forces created when compacting earth inside of them. We are building a series of strong backs (2x12 vertical supports) that support wailers (2x10 horizontal planks) that back onto the form ply.  Both the wailers and strong backs were milled from the Douglas fir timbers that were harvested on site.
2x12 Douglas fir strong backs with 2x4 wailer supports.  They are built for walls up to 16 feet tall.
All lumber shown was harvested on site.
"X's" for connecting the inner and outer wythes of the rammed earth walls.
"L's" for connecting the walls to the concrete slab to aid in seismic stabilisation.
"Foamglas" material.  These are impervious blocks of glass bubbles that can bear load.  They will be used below the inner wythe as shown in the drawing of Wall A near the beginning of this blog.  They help keep the thermal envelope more continuous.

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