Mixing and Blending

Rammed earth is traditionally made from the soil the building stands on, and this remains a preferred solution. In many places in the world this remains the case, and this allows substantial buildings to arise where vehicles and even the roads they need travel on are in short supply. The Kasbahs of Morocco, the Dzongs of Tibet, the barns of central France and the Great Wall of China were all built from the ground they stood on.

So for these buildings there is only the matter of mixing to consider. Unless of course the material could be improved with the addition of material from near or far. This might be the addition of one of the basic ingredients, clay, sand or stones. Or it might be that for some reason burnt lime, bitumen, blood, casein or some other 'exotic' might be added.

Mixing is either manual or mechanical, both can be highly effective, both can be poorly done, both can use more energy than is strictly necessary. Given the mass nature of the material doing anything more than is necessary should be avoided

Manual mixing can be done with a shovel, spade or highly effectively with a hoe. It may be that if you are extracting the material on site how you dig can also help the material mix at the same time, by digging across the face of a slope or 'cliff' rather than sinking a hole or shaft. Using the landform to help extraction can also be an effective way to mix.

Once extracted material may need further breaking up, may need turning to reduce or increase the moisture content. As much as possible handling should be kept to a minimum, it's hard work! But we have found that hoes are a highly effective way to handle material, increasing the work rate without increasing the energy used.

Mechanical mixing can be done in many different ways. The one thing that doesn't work well is a standard cement mixer as this is designed to mix liquids and rammed earth mix is too dry. That said big horizontally mounted cement mixers can work as the breaking action is different to a mixer which is mounted at an angle.

Front end loaders, backhoes, drum or forced action mixers, even tractor mounted muck spreaders have all been used very effectively. As with manual extraction using the right bucket of a digger can help to break the material up as part of the extraction process and this will reduce the time taken in mixing.

Whether by hand or machine adding materials to the mix can be done more or less easily. Making dry mixes is less hard work than making mixes with water added so adding dry powder clay is advisable over adding already wet clay. Likewise adding dry sand and gravel together before adding clay is much easier.

Finally adding water is the most labour intensive activity as the clay becomes more active and stickier. Its also the thing to take most care of, too wet a mix and you will have to wait while it dries out again, both expensive and time consuming. When working in wet conditions it is better to keep the mix a little dry so that rain is adding water to the mix for you rather than working against you!