Water

Do not underestimate water. It is one of the most common chemicals on earth, but it is also one of the most complex substances a surveyor will come across. It is a potent agent of decay in houses and is the cause of the majority of complaints from occupants.

'The smallest hole will eventually empty the largest tank (unless it is a drainage hole, in which case it will block).'

Key characteristics of water/water problems

• Water can travel a long way inside a structure before it exits (up to 15m).
• Corners and folds are weak spots in a building.
• Large stains can be caused by small amounts of water.
• Water is as harmful to houses as a vapour as it is as a liquid.
• Building materials can act as a wick, drawing water to areas where it can evaporate.
• Rain can travel vertically up a wall when driven by wind, yet most drip details assume rain will always run down a building.
• Water travels further through smaller gaps.
• Water can enter a building through multiple locations yet emerge in the same place.
• If a leak is caused when it rains, then knowing when the leak starts and stops in relation to the timing of a downpour is critical.
• The quicker water gets away from a building, the better it is for the building.
• Water-tolerant details are usually better than watertight details.

Facts that demonstrate that water is far from ordinary:

• It floats in its solid state.
• Unlike most chemicals, it exists naturally on the planet in all 3 physical states: solid, liquid and gas.
• It expands by 8% when it freezes, and can exert a force of 2 tons per cm2 as it expands.
• Water dissolves more substances than any other liquid.
• There are 12 different types of ice.
• Hot water freezes faster than cold water.
• It takes as much energy to take ice from 0°C to water at 4°C as it does to raise the temperature from 4°C to 80°C.
• A glass capillary tube 0.2mm in bore will lift (approximately) a 140mm column of water.
• Water has unusually high:
  • melting point;
  • boiling point (water has higher than expected boiling point from extrapolation of boiling points of other group 6A hydrides);
  • surface tension (it can bounce);
  • viscosity (it has unusually high cohesivity for a liquid);
  • heat of vaporisation (the highest heat vaporisation per gram of any molecular liquid).
• Water has a high density; it is at its most dense at just above freezing point (at 3.894°C); density then falls with temperature (hence convection in a heated vessel).
• Additional pressure reduces its melting temperature.
• Pressure reduces the temperature of maximum density.
• The speed of sound through water increases with temperature (up to a maximum at 74°C).
• Water's viscosity decreases with pressure (at temperatures below 33°C).
• Water has the second highest specific heat capacity of any known chemical compound, after ammonia.
• Water has unusually low compressibility. The compressibility drops as temperature increases, down to a minimum at about 46.5°C. Below this temperature, water is easier to compress as the temperature is lowered.
• Water's thermal expansivity reduces increasingly (becoming negative) at low temperatures.
• Water has over twice the specific heat capacity of ice or steam.
• Solid water (ice) exists in a wider variety of stable crystal and amorphous structures than any other material.
• The refractive index of water has a maximum value at just below 0°C.
• The thermal conductivity of water is high and rises to a maximum at about 130°C.
• Under high pressure, water molecules move further away from each other with increasing pressure.
• Water vapour as a gas moves from a centre of high concentration to low.
• The electrical conductivity of water rises to a maximum at about 230°C, and then falls.
• Warm water vibrates longer than cold water.

Relative humidity (RH)

• RH 85%+ over a sustained period causes microbial decay in materials, especially timber.
• RH 75%+ over a sustained period causes mould growth.
• RH 70%+ over a sustained period causes condensation if rooms are not vented.
• In a healthy well-vented house, RH is between 30% and 70%.

Moisture content in timber

• Under 17% is safe.
• Over 20%, decay is inevitable.

Common sources of moisture containing chloride and nitrate ions

Sulphates can also be found in ground sourced dampness and from the atmosphere in industrial areas, leading to failure of concrete solid floors and deterioration of mortar and brickwork. See Rubbing sat in the wound for more information.

Sulphuric acid can also be produced when, for example, rainwater penetration and/ or condensation forming in chimney cavities comes into contact with flue salts arising from the burning of wood and coal.