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Wimpey No Fines In Situ Concrete House  


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The Wimpey No Fines In Situ Concrete House.

  • Manufacturer: George Wimpey & Co Ltd
  • Type: In Situ Concrete
  • Number Built: 300,000
  • Period Built: 1940's-60's
  • AKA: Formwall - Gateshead AMD

Wimpey No-Fines Introduction

The phrase "No fines" relates to the name of the type of concrete that was used in the construction of this system of house building. No-Fines concrete is a non-proprietary material used widely in England and Scotland for the construction of walls in dwellings. It comprises of a mix of concrete that contains no sand or other small particles of very fine gravel, collectively known as 'fines'.
Often the mix used contains 3/4" or 1/2" sizes stones or gravel as the sole aggregate constituent. This mix creates a honeycomb structure within the concrete leading to a product with a higher insulation value (lower U-value) when compared to standard dense concrete.
The No-Fines mix is 1:10 with 20mm aggregate.

No Fines Aggregate

George Wimpey & Co Ltd developed their own patented housing construction system using no-fines concrete which resulted in the production of  around 300,000 low rise dwellings in the UK from the 1940's onward.Wimpey
The Wimpey houses were built mainly for Local Authorities across the country due to the speed of construction and the reduced need to employ skilled bricklayers who were often in short supply.
Most Wimpey no fines houses were built between 1947 and 1977. This form of construction tended to die out when cheap high insulation blockwork became readily available.


Structure

Foundation
Previous investigation of this type of house revealed that the foundations are generally conventional. Typically comprising of concrete strip footings laid atop a brickwork substructure that supports the external walls above.
External Walls
Generally, the no-fines external walls are approximately 12-13" thick, with a 1/2" - 3/4" " pebble dashed render finish externally and a 1/2" - 3/4'' hard plastered finish internally.
The external walls incorporate a series of steel reinforcement bars within cast in-situ dense concrete beams at eaves level.
Precast concrete lintels are incorporated into the no-fines walls to provide support above the ground floor openings. Projecting reinforcement from the lintels is lapped to continuous horizontal tie reinforcements located within the no-fines walls at first floor level.
Floors
The ground floor is of a solid concrete construction.
The first floor construction consists of timber joists onto which a tongue and grooved floorboard finish is fixed.
Roof
Generally, roofs are of traditional pitched timber rafter/ purlin construction, clad with interlocking roof tiles on felt and battens.
Other
The party wall construction is formed from no fines concrete, whilst internal partitions are typically of traditional masonry construction with both having a hard plastered finish.
Ceilings are formed with plasterboard.
The chimneys are of standard brick masonry construction.

Identification: Wimpey No-Fines

Cross section diagram wimpey no fines house

Built as bungalows and 2-storey semi-detached and terraced houses. Wimpey also produced flats, huts, commercial, civic and school buildings.

Houses generally have a medium pitch, hipped or gable roof covered with tiles, or sometimes a flat or a shallow valley roof that is covered with bituminous felt or asphalt.

External walls were coated in render throughout, or render to front and rear walls with the flank walls being of brick. Precast concrete corbels were noted to gable end eaves.
Some dwellings have bay windows to front.

Notes For Surveyors

  • Vertical cracking has been noted to no-fines concrete of external walls.
  • Horizontal cracking of render noted above window drips.
  • Scarcity and corrosion of wall ties to brick cladding.
  • Attention to variable high and low rates of carbonation of dense aggregate concrete ring beams.

Additional Information

The purpose of this form of construction was to reduce cost and leave the wall aerated and thus aid insulation. The wails are un-reinforced and rely on their mass for strength. The concrete was formed in-situ usually from a batching plant on site and the formwork used to frame out the wall removed after the concrete had set. It is normally the case that “No Fines” construction in domestic dwellings does not have a cavity.

In the case of some houses vents in the walls were found in the pantry area or boiler location. In a number of inspections there was no evidence of a cavity or any evidence which would suggest if a cavity ever existed. Cavity wall tie failure was found at a number of location.

In one house surveyed, the external walls and central party walls were found to be of ‘no fines concrete’, with the external face of the walls rendered to increase weather protection.

General Points

It can be difficult to replace the exterior render. The render achieves an excellent key with the concrete. As the concrete has no sand, sections can sometimes break away easily whilst removing the existing render. The same applies to internal plaster walls if they have not been dry lined.
As there is typically no cavity the walls can be affected by water ingress caused by leaking gutters etc. This was particularly evident in cases where the render was found to not be weatherproof.

Insulation in properties of this form of construction do not live up to expectations or current standards. Dry lining and additional render may help to solve this to a certain extent.
This method of construction was unconventional. As a result, some prejudice against this system was encountered. It should be noted that his form of construction is not classed as defective under the Housing Defects Act 1984.
Alterations and repairs to walls can sometimes prove more difficult than repairs undertaken to conventional types of brickwork.

Conclusion: Generally speaking, local authorities who hold this type of housing stock, report no significant issues other than those mentioned. This does not exclude faults or issues that have not been reported.

ADVANTAGES OF NO-FINES CONCRETE:

  • 1. Density of no fines concrete is very low.
  • 2. No fines concrete does not segregate and the capillary movement of water is almost nil.
  • 3. Better thermal insulating characters achieved by the presence of large voids.
  • 4. Concrete can be dropped into place from a permissible height.
  • 5. Shrinkage is lower standard concrete.
  • 6. It is lightweight.
  • 7. Allows for the early removal of formwork.
  • 8. No mechanical vibrator is required for compacting no fines concrete, a simple rodding method is sufficient for full compaction.
  • 9. It gives better and attractive appearances.
  • 10. Production costs are lowered through reduced cement content.

DISADVANTAGES OF NO-FINES CONCRETE:

  • 1. The strength of no-fines concrete is comparatively lower than standard concrete.
  • 2. No-fines concrete cannot be used in reinforced concrete structure.
  • 3. The consistency of no-fines concrete cannot be reliably measured.

External Wall Insulation (EWI) for Existing Properties

Solid wall or non traditionally built properties including Wimpey "No Fines", can have issues relating to heat loss. Retaining heat can be difficult as the thermal properties of the existing walls can allow for the rapid transfer of heat from the inner face to the outer leaf.

This can inflate energy bills and make budgeting through winter periods extremely difficult. Often the external walls of this type of property can experience degradation due to damp and moisture ingress which can sometimes lead to wider scale of structural and non structural defects.
One remedy to tackle poor thermal performance and increase the weather resistance is to wrap the building in an external wall insulation system commonly referred to as EWI. This type of external insulation is available in a wide variety of insulation materials and exterior finishes that will compliment any suitable property. One of the most cost effective insulation materials for most refurbishment projects is Expanded Polystyrene otherwise known as EPS. This is used in conjunction with advanced polymer based pebble dash or smooth silicone finishes. Specialist finishes are also available including brick slip effect render, real brick slips and other feature details such as quoins and header courses.

Additional EWI Benefits

Additional benefits to EWI include increased acoustic insulation, maintenance reduction and the aesthetic improvements that the building receives, which can often be transformative. Thermal performance improvement can also dramatically increase the building's Energy Performance Certification (EPC), whilst also reducing energy demand and reducing fuel bills. Properties treated with EWI typically increases in value by up to 38% in some parts on England, based on a study conducted by DECC.

EWI plays a significant role in regeneration schemes across the country. Evidence shows that streetwide refurbishment of existing housing can dramatically improve a streets appearance, increasing pride and reducing crime in certain areas. EWI can also help to increase the expected life expectancy of many properties by several decades to the added level of protection that EWI provides.

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