Monday, 29 June 2015

Strong Rammed Earth Basics and the Animals on Site

Welcome to the weekly update on The Cabin in the Woods.  Its been a hot week of milling and stacking lumber.  Recall that all of the lumber was harvested on the site with the intention of using it to construct parts of The Cabin in the Woods.  

We had several visitors on the site this week ... electrical inspectors, relatives, some enthusiastic friends who are passionate about building with rammed earth themselves, and quite a few four legged visitors as well.

A fawn and mother deer nursing.  These two are almost tame.  

We have nearly met all of our lumber requirements and now we just need to be patient and wait for the wood to dry out in the air.  Shade or cover definitely helps the wood cure straight and free of checks and cracks.

Extra long 2x10's and 2x12's that will become the strong-backs and wailers in our rammed earth formwork.  After the rammed earth walls are built, these boards will be re-sawn into suitable sizes or used elsewhere in the project.

A stack of 6x12 fir which will be used as beams in the Cabin in the Woods.  Beside the beams is a pile of 1x material to be used in a future footing form-work application or where aesthetics are not crucial (these are seconds).

Creating strong rammed earth mix designs is possible nearly everywhere there is sand and gravel available.  Very few locations have soil suitable to use the dirt directly from the building excavation. Although using this material would have many ecological and cost advantages, there are problems inherent in the lack of consistency and materials present in the resulting soil.   Almost all locations have a gravel pit within five to ten miles that can provide consistent screened (not washed) sub-soil excavations that can meet engineering strength requirements.  Sub-soil means below the top soil and containing no organic material or top soil.

Several properties of soils which will affect the strength of rammed earth are angularity, gradation, clay and silt present in the finer particles of the mix, and it seems there is a dash of luck or chance thrown in to the mix too.   The chemical composition of the sand and aggregate in the mix can also have an adverse or positive affect on rammed earths overall strength.

Traditionally rammed earth was compacted by hand using tamping poles.  Using Pneumatic ramming tools will nearly double the compressive strength of any rammed earth mix.

A floor rammer.  These are pneumatic tools used in foundries to compact sand or for compacting backfill in trenches or pole bases.  They are perfect for consolidating rammed earth into formwork.  Using a pneumatic rammer to compact rammed earth almost doubles the compression strength when compared to rammed earth compacted by hand.  

The foreman making sure all the lumber is properly drying.
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