Biological Agents

• Attack by rodents , insect , fungi , algae , & plants may cause serious deterioration in various parts of a building .
• Rodents may cause considerable damage to timber & other organic material .
• Insect attack is generally confined to timber , but some other materials derived from organic fibres or pulp may also be affected .
• Fungal attack occurs only in the presence of sufficient persistent moisture . Fungi are parasitic & attach themselves to surface which supply nutrients .
• Algae , being chlorophy11 - bearing , grow on walls ob buildings to which they are transferred by wind as spores . Algal growths resemble dirt deposits on external paint surfaces & porous concrete .
• Plant life in the form of ivy , moss & lichens , if allowed to develop , will cause deterioration of the material surface & the jointing materials . The damage is done by the penetration of roots into crevices as they grow to extract moisture from the damp materials .