Algae are very small, simple plants, which can colonise damp, rough surfaces. Because they are green, they are very visible, and can cause unsightly staining. Heavy local algal staining of walls is an indication of dampness, usually due to failure of, for instance, rainwater disposal.
If the outer skin of a concrete structure is badly affected by water it can break up, allowing moisture to penetrate the structure, and causing rusting of the steel reinforcement, which splits the concrete. This 'rotting' of the concrete is known as 'concrete cancer'.
Minor cracks occur in many buildings, due to expansion and contraction as the building warms and cools, or during slight settlement, usually soon after the building is completed. It is important to find out the reason for the cracking. Cracking is worrying if the width or length of the crack is increasing, or if the individual masonry elements fracture. In that event a structural engineer should be consulted, urgently.
Used to describe the decay of a stone by the peeling off of outer layers (as in an onion), especially common when a stone is face-bedded.
A term used to describe a building, or element of a building, which is suffering from a long-term problem.
A fungus (scruple lacrymans) which lives on damp wood, destroying its cohesion. It needs dark, damp and unventilated space to thrive. Affected wood loses all its strength and breaks up into roughly cubic blocks. The fungus is aggressive, and can spread very rapidly. Early signs of an outbreak are red or brown dust (spores), dark tendrils in a veined pattern, and 'mushrooms' (fruiting bodies). The first steps to be taken when an outbreak is discovered are to ensure that it is not affecting the stability of the building, to remove the cause of the dampness, and provide ventilation to dry out the wood. It is wise to seek the advice of a conservation architect before bringing in a contractor.
When white crystals appear on the surface of masonry, or plaster, these are referred to as 'efflorescence'. The phenomenon is due to the movement of mineral salts from the body of the stone to the surface, as a result of movement of moisture. It may be an indication of water penetration or condensation, and thus a need for repairs.
This term is used to describe the decay of the body of a stone. It is usually the result, either of the use of a very soft stone, or of the decay of the bonding material that holds the stone particles together. It occurs as a long-term effect in a windy location (often on the side away from the wind), and is commonly accelerated by wetting and drying, by the application of salt in winter, and by unsuitable stone-cleaning techniques.
Here used to refer to a surface fungal growth, not harmful to structure, but unsightly, and often with an unpleasant smell. Moulds can cause breathing difficulties in susceptible people. They generally grow in spaces which are not properly ventilated.
A condition of roof in which the nails fastening the slates to the sarking have rusted away to the extent that the slates begin to slip over a significant area.