Loam is a natural mixture of clay, silt and sand, in which the clay fraction acts as the binder while sand and silt form the skeleton. It is not a manufactured product but a soil type — and at the same time the oldest building material in the world, dug almost anywhere straight out of the ground.
The ratio between those three fractions governs the behaviour: a high clay content gives a rich, strongly binding but strongly shrinking loam, while a high sand content gives a lean loam that barely binds. Building loam is therefore nearly always adjusted — with sand to limit shrinkage, or with clay for more binding power.
Loam, clay and loess
- Clay consists of extremely fine plate-shaped mineral particles and is the binding component.
- Silt sits between clay and sand in particle size.
- Loam is the mixture of these fractions, with or without coarser material.
- Loess is wind-deposited fine silt and forms the fertile loam soils of many regions.
- Boulder clay is loam deposited by ice sheets with stones in it; it is dense and poorly permeable, which matters for drainage and infiltration.
Loam as a building material
Loam does not set chemically like cement or lime — it dries. What has dried can be softened again by water. That is at once the strength and the limitation of the material:
- Fully reusable. Old earth work can be wetted, remixed and reworked — with virtually no loss and no waste.
- Very low environmental impact. Nothing is fired; the energy is essentially all in transport.
- Moisture buffering. Loam takes up water vapour when the air is humid and releases it again when the air dries out. In a loam-plastered room the relative humidity stays remarkably stable — good for comfort and for timber components.
- Thermally massive. Solid earth work is heavy and stores heat, damping summer temperature peaks. What loam does not do is insulate: for that you need a separate insulation layer, or a light loam with straw or wood fibre.
- Not water or frost resistant. Unprotected loam washes away, and frost in wet loam causes damage.
The rule of thumb of earth building
Earth building calls for a good hat and good boots: a generous roof overhang that keeps the wall dry, and a water-resistant plinth of stone or concrete with a sound damp-proof course, so the loam never stands in rising damp or splash water. Where those two conditions are met, earth structures last for centuries — the countless timber-framed houses with earth infill panels prove it.
Applications
- Infill panels with staves, wattle and straw-loam between the timber studs.
- Adobe blocks, rammed earth (pisé) and loam blocks for internal walls.
- Clay plaster as a finish to walls and ceilings.
- Loam boards on battens, as a dry and fast alternative.
- Raw material for bricks and roof tiles, which only become frost and water resistant through firing.
Related terms
- Clay
- Boulder clay
- Adobe block
- Clay plaster
- Claystone
- Expanded clay pellets
- Sustainable building
Want to know more about building terms? Take a look at our knowledge base on fredsdiyplans.com.