1 1.10 Trampling The traditional way of mixing tempered earths is to place the material in a pit or on a flat clean surface and to trample it using either a large squad of labourers or heavy animals such as oxen or horses. When carrying out this task using labourers, it is essential that they have heavy, well fitting laced boots. The best action is obtained using the heel of the boot rather than the whole sole. "Heeling" is also the traditional way of applying puddle to the base of canals or aqueducts.
MIXING
1 1.08 Forks A fork is a pronged agricultural implement used for digging, lifting, carrying and throwing. It has been developed for working heavy mixes or materials containing a high percentage of fibre. When turning heavy clay soils or heavy tempered mixes, a fork is easier to use than a spade. It can also be used to form a rough dressing to mudwvall as it is being built, making the surface easier to pare to the correct plane.
The trampling effect for mixing materials can be achieved mechanically by laying out the materials on a solid base then driving a tractor back and fonvnrds over the mix. Whether using a tractor or traditional trampling, the flattened mix must be regularly turned over and piled up before repeating the process till the desired mix is achieved.
1 1. I I Mechanical Mixers Various types of mechanical mixers are available that are capable of mixing earth mortars, but, as the mives should be kept as dry as possible, only heavy duty equipment is successful.
Forks
The ordinary cement mixer is useless for this type of work as the stiff mix sticks to the blades inside the drum and simply revolves wvith the drum without any mixing action taking place. A motor driven pug-mill with two pulverising wvl~eels can handle about 71n"er day. A horse driven pugmill suitable for this type of work was surveyed by RCAHMS on Islay, Argyll.
1 1.09 Riddles A riddle is a coarse sieve used to size gravel, cinders, earth, etc. A set of riddles is useful to ensure that there is no oversized aggregate or lumps of other material in the mix.
Linear mixers are widely available in Europe. There are a number of variations each adapted to the type of mix required and the weight of the soil. Some operate with a single-shaft, others with double-shafts: some are designed to operate on a continuous flow action, others on discontinuous flow. Capacity ranges from 4 to 5m2 per day for the smaller machines to 50m2 per day for the largest. A similar h e a d i n g action can be obtained from a second-hand commercial dough-mixer as used by some of the larger commercial bakeries. This type of machinery is used for many commercial potteries for mixing their clay. Vertical mixers can be made using basic materials. These are horse driven and have not been examined by the authors but designs may be available from CRATerre-EAG, Grenoble, France. Concrete mixers, screw mixers and planet wheel mixers can all be used for mixing muds or plasters but generally these are not suitable for structural earth-building mixes.
TAN 6
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Earth Structures