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All About Green Building Materials (page 2 of 3)

Learn about different types of eco-friendly bricks, blocks and other building materials.

Excerpted from Do It Yourself Home Improvement

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Finishes

The most common finishes for green materials are lime-based. Lime mortars and stuccos are considered greener than modern cement and gypsum-based stuccos because, although their manufacture gives off carbon dioxide, it is reabsorbed as the lime sets, making it a carbon-neutral product. Lime is also recyclable and biodegradable.

It is important to ascertain the type of mortar needed for a particular green block. While it will usually be lime-based, the particular type and strength of a mortar may be crucial.

Non-hydraulic lime
This mortar is so called because it does not harden underwater. It is produced by heating a pure form of limestone to a very high temperature, burning off carbon dioxide and leaving quicklime. This is then mixed with rainwater to form lime putty — a process known as "slaking."
Lime putty (Image 1): Left to mature for a number of months, lime putty is the raw material in stuccos and mortars that are completely lime-based. It is mixed with sand to create mortar.
Non-hydraulic hydrated lime (Image 2): Sold in bagged powder form, this has had less water added to it during production than lime putty. It is considered inferior to mature lime putty.

Hydraulic lime
This mortar is produced by heating up a less pure form of limestone than that used for non-hydraulic hydrated lime. The impurities found in the mix include materials such as clay. The manufacturing process for hydraulic lime means that it dries to a more hardened finish than non-hydraulic lime. It is breathable, but is much less flexible than non-hydraulic lime.
Hydraulic lime (Image 3): The manufacturing process for hydraulic lime means that it dries to a more hardened finish than non-hydraulic lime. It is breathable, but is much less flexible than non-hydraulic lime.

Additives
Sometimes small amounts of portland cement are added to lime, to hasten the setting processs. Purists do not do this, due to the possibility of segregation occuring as the mixture dries. Animal hair — typically horse or goat — can be added, as can modern, synthetic products. Minerals called pozzolans, which allow the mortar to harden quicker, are also used.
Horse hair (Image 4): For stuccos, horse or goat hair may be introduced to the mix. This lessens the chances of cracking in mortar that is still drying, or mortar that is prone to flexing.

Working safely
When mixing lime and water, be sure to add the lime to the water, and not the other way around. This is particularly important when making lime putty from quicklime, as there can be a risk of explosion. Lime is a skin, eye and respiratory irritant, so wear protective clothing.

Excerpted from Do It Yourself Home Improvement

© Dorling Kindersley Limited 2009

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