This form of construction involves the use of no-fines concrete, ie concrete containing cement and graded aggregate (often 12 or 19mm in size), but no sand nor fine aggregate. The lack of fines results in a wall that can be cast more economically than a normal concrete mix and which contains many air gaps, giving some improved insulating capability. It is also more resistant to damp penetration as its wide pore structure reduces capillary action (refer to Chapter 14 on Damp).
The first recorded no-fines house was constructed on the Isle of Wight in 1852 and several hundred were built in England and Scotland between the wars. Over 72,000 of these low and medium rise houses were constructed by Wimpey in England and Wales from 1945 to the early 1960s and a further 128,000 between 1964 and 1979. Several thousand were erected by a number of other contractors, whilst in Scotland, the Scottish Special Housing Association, Wimpey and other contractors commissioned or constructed several thousand more. The majority of the dwellings were low/medium rise, although a certain number of high rise buildings were constructed.
The Wimpey version had external walls formed with 200-300mm thick no-fines concrete poured on site into prepared shuttering containing continuous reinforcement. External elevations were
finished with a wide range of materials, although cement render was very commonly applied. Internal walls were of breeze blocks or timber studwork. Very little prefabrication was involved except for the shuttering panels which were re-usable.
Common problems include:
• Rotting windows and external doors caused by poor joinery design and/or inadequately sealed gaps between joinery and structure.
• Excessive heating loss due to poor thermal insulation. This is often combined with an inadequate or expensive to run heating system.
• Surface condensation and mould as a result of poor ventilation, cold bridging, and inadequate thermal insulation/heating.
• The wall construction should reduce capillary action but there have been rainwater penetration problems
• Cracking and spalling of render on external wall faces often caused by lack of suction in the no-fines concrete, or unsuitable mortar mixes, eg strong over weak.
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