Buildings and natural finishes

Building design

Lime- and earth-based plasters, renders and paints are highly suitable, if not essential, for use in conjunction with sustainable and traditional wall-building materials. Examples include earth (clay), timber, hemp, reed, straw-bale, low-energy bricks and stone. Many of these traditional walling materials have been used successfully for thousands of years and are now enjoying a renaissance, as the foundation for many of the contemporary 'eco-building' methods. A unifying characteristic between these walling materials is that they are all, to a degree, porous. They allow the free passage of moisture into and out of them, and therefore need to 'breathe' to remain healthy. Because of this, they are highly responsive to changes in relative humidity and temperature in the atmosphere. This means that structures made out of these materials will naturally move in response to these differences. All finishes applied to these materials must therefore match the hardness and porosity of the walling substrate below. They must be flexible enough to accommodate natural movements in the building without cracking, and need to have a high degree of vapour permeability to eliminate the potential for trapping moisture within the wall. A case can also be argued for the use of lime- and earth-based plasters, renders and paints (with certain preparatory measures in place) on some of the modern, conventional building materials, such as concrete block and plasterboard. Though their qualities of softness, breathability and flexibility are not essential when used with these conventional materials, lime- and earth-based finishes can bring benefits in the areas of decreased impact on the environment (their production, toxicity and ease of disposal), improved internal air quality, and by improving the look and general 'feel' of the building and the spaces inside.

Wall systems

This section introduces different walling systems that are compatible with lime and earth-based finishes. It also outlines the suitability of applying the various finishes to different substrates.

Earth walls

Earth walls can be constructed in many different ways. Building with earth (clay-rich subsoils) is the most ancient of all building methods. Many variations of earth building have been used throughout the world since man began building shelters. Most earth building methods consist of mixing together a clay-rich subsoil with other ingredients. These are most commonly some form of fibre (straw) to provide tensile strength, and aggregates to provide strength and stability to the mix. Most buildings made out of earth must be raised off the ground at least 450 mm (18?), and should have large roof overhangs to protect the walls from rain.

Many of the earth building methods are currently enjoying a revival because they provide a sustainable way of building. This is because most forms of building with earth have an incredibly low environmental impact, especially when locally resourced materials and simple techniques are used. Earth building materials can be indefinitely recycled, and biodegrade easily. They have tremendous health benefits, such as temperature and humidity regulation, high thermal mass (they can absorb and store large amounts of heat), good toxin and odour absorption, and excellent sound insulation properties. Some of the earth building variations include:

Monolithic earth walls, such as cob, clob, wychert, clom, mud, clat, clay & clunch

A load-bearing walling system – an ancient building technique and material that is used throughout the world, with regional variations, such as 'cob' in the southwest of England. It is composed of clay subsoil, aggregate and straw. These ingredients are mixed together with water to produce a homogenous, malleable and sticky material, which is laid in 'lifts' of 300-600 mm (12-24?) in one building session. Once the previous one has hardened, consecutive lifts are laid until full wall height has been reached. The cob is built up without forms or shuttering, but is compressed in place by foot or with a garden fork. It is then trimmed with a sharp spade to maintain a plumb line.

Unfired earth blocks, such as adobe, cob block, and clay lump

A load-bearing material used throughout the world for thousands of years. This is a system of creating building blocks out of raw clay-rich subsoil, aggregate and sometimes fibre. The material is either moulded in a plastic state into forms, or compressed by machine in a dry state. The blocks are laid in bonded courses, with either a mud or lime mortar, or simply wetted down and bonded through suction if the blocks are made with dry material.

Rammed earth & 'pise de terre'

Monolithic earth walls built up between temporary shuttering. A load-bearing material, which is sometimes mixed (slightly moistened) with aggregate, or it can be used in its raw form if the right proportions naturally exist. It is tamped by hand or with a pneumatic tamper, between wood or steel shuttering. The shuttering is moved up until full wall height is reached.

Light clay & light straw clay'Leichlem' (pronounced 'lie-klem')

A non-load-bearing walling material. Straw is coated with a clay-rich slip which is compacted between temporary shuttering, set within a timber structure.

Wattle & daub

A non-load-bearing walling system of tightly woven sticks (usually a green and flexible wood, such as hazel, willow or maple), set within a timber-framed panel. This lattice (the wattle) is then coated with a 'daub' mixture: a thick clay-rich subsoil mixed with chopped straw or hair, and sometimes animal dung for extra weather resistance and durability. This is squeezed into place between the sticks. The daub can either be finished with a limewash or coated in a lime plaster/render for extra protection. It can be used for exterior walls or interior partition walls.

All lime- and earth-based finishes are ideally suited for all types of raw earth construction. Cement and synthetic paints must not be used.

Straw-bale wall construction

Straw-bale wall construction originated in the USA around the end of the nineteenth century. It coincided with the development of baling machines. The straw bales are used like large building blocks, stacked on top of one another in staggered courses. They are usually speared onto pins – often sharp rods of hazel or steel. This ties them into the foundation and provides structural stability for the walls. There are many different methods of building with straw bales, but these can be broadly categorized into (a) load-bearing, where the bales take the full weight of the roof, and (b) non-load-bearing, where the bales are set within a timber structure and used as a wall infill between the posts....