Bulding

Building with Hemp and Lime
By Ranyl Rhydwen, edited for Distance Learning by Damian Randle This lecture investigates hemp and lime as a building material, in use, and covers the properties of lime, characteristics of hemp and lime construction, thermal performance, costs, and quantities, building issues, and then finally hempcrete specifically: CO2 emissions and potential market. In the bookyou will find the ‘sister piece’, ‘Hemp (Cannabis Sativa L.)’, which should be read in order to understand the historical, agricultural, environmental and economic background issues.

Lime
Lime has many environmental problems associated with it. - It is mined on a large scale. - It has a moderately high embodied energy (800kg / tonne). - It is a finite resource. - It is processed centrally awayfrom the mining operations, necessitating the high haulage costs of a heavy material (heavy loads cause more CO2 emissions and pollution)( WWF 1994). - Lime Kilns use fossil fuels. - It is associated with biodiversity loss due its mining operations and its contribution to global warming. Despite this are many benefits to using lime. The following are the advantages of using lime as a plaster,render, and mortar in buildings; 1. It is “breathable” (high porosity, high water vapour permeability): breathable walls control internal humidity, reducing condensation and preventing mould growth. This improves the indoor air quality and the health of a building’s occupants. 2. Low thermal conductivity - ~1 W/(m K) - and a moderately high specific heat allow the plaster to act effectively as athermally massive heat store, contributing to the thermal comfort of the internal environment. 3. Lime is a long lasting material. (For example the Pantheon in Rome). 4. Lime is easily recyclable (re-burnt to form hydrated lime or used as aggregate) or is naturally absorbed into the land without causing toxicity. 5. Autogenous Healing: as lime buildings move small cracks can appear. Water penetratesinto the cracks and dissolves any free lime. This brings it to the surface where the lime carbonates and heals the crack automatically.

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6. Protection: lime acts as a very good ‘sacrificial’ external surface, protecting the essential structural elements of building from the weather, fire and vermin, although it must be maintained. 7. Lime mortars protect stone work and bricks, enabling themto be easily recycled, reduce material usage over time and lessen the need for major building repairs (Holmes and Wingate (2002), p..62). 8. Lime mixtures have good workability and are well suited for plastering. 9. Lime is alkaline, preventing mould growth and making it undesirable to small animals. 10. Lime washes are breathable and aesthetically appealing. 11. Lime allows for relatively easybuilding maintenance; regular lime washes or re-pointing prolong the longevity of a building. Sources: May (1998), Holmes and Wingate (2002), Building with lime forums (2005), BRE (2001). Lime is reasonably difficult to use in comparison cement and is more labour intensive. It requires patience to work with and careful site management to ensure the material sets properly. Lime requires several coatsover several days, has to be cherished (kept moist) and protected from the weather for up to a week for successful application. It takes time for lime renders and plasters to fully set (several months) and it can be damaged by frost before becoming fully set (Holmes and Wingate (2002), p. 126) meaning that construction is weather dependent and external work is not recommended in the winter months.All of these considerations mean that lime has become unpopular in modern, fast, economically driven building sites where time is money (May 1998). To minimize the environmental impact of lime, the smallest amount of lime possible should be used that maintains the benefits of using it outlined above. The carbon dioxide emissions, pollution, waste, haulage requirements and landscape disruption...