Buildings and natural finishes

Wall systems

Moisture issues

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.

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