In-Situ Concrete Laing Easiform House

Manufacturer: J Laing Construction Ltd
Alternative name: Easiform
Period built: 1919–1928
Number built: 2100

The Easi-Form method of building was first designed by Laing and Co in the early 1900's which involved pouring concrete into various types of mould designs which had been set up on site, otherwise known as in-situ.
The first house was successfully constructed in 1919, and a further 5000 dwellings were built during the inter-war period, with construction peaking in the mid-1920s.
The now proven Easiform system was swiftly reintroduced shortly after the war in 1946 and production continued right through to the early 1970s providing around 85,000 dwellings in total.

Due to the walls being constructed from cast-in-situ concrete using varying types of mould layouts, the system was adaptable, easily allowing for a wide variety of layout configurations which could be easily adapted for different types of accommodation.
Over 25 different types of Easiform buildings were produced, including houses, flats and maisonettes.

Two, three and four-storey buildings were common and roof designs included hipped and gabled roofs. Front porches were frequently varied in design, with some properties benefitting from bay windows and even the application of brick skin outer cladding to the front, rear or side walls, giving the outward appearance of traditional brick construction.

Structurally the Easiform house was essentially built in a very similar way to a traditional cavity walled brick dwelling. The poured concrete was moulded in-situ into into a inner and outer skin with a central cavity.  The floor and roof loads are carried directly down to the foundations via the load bearing inner skin of the external walls, which were stabilised and stiffened using wall tie connections from the inner to outer skin.
This system was strong yet simple and could tolerate even considerable damage without affecting the overall stability of the structure. Cast-in-situ cross walls also provided substantial lateral bracing, and in the very unlikely event of partial failure of an external wall, damage would not necessarily spread to the remaining structure.

Two Storey Laing Easiform - Built during 1919-1928

The very early and now very rare Mk1 versions of the Easiform houses had 8 inch thick solid concrete walls, built using no-fines clinker concrete. Typically, No-fines concrete of the time contained no fine sand, hence the term 'No-Fines', and often used single size stones or in this case 3/4 or 1/2 inch clinker as the main aggregate. Around 2100 were built using this method before 1928.

Properties Built during mid-1920s to 1945

The more common Mk2 version had cast in situ cavity walls, 3 inches (7.6 cm) thick inner and outer Leaves with 2 inches (5.1 cm) cavity, usually finished externally with stone dashed render coat.

All cavity-walled Easiform constructions were constructed using a similar principle to traditional brick cavity construction as mentioned previously. The external skin of the cavity was cast using normal dense gravel aggregate and the internal skin was cast using clinker aggregate concrete, linked together using conventional wall ties.

In the first cavity-walled Easiform dwellings, the outer skins were 3 inches thick with a narrow 2-inch cavity. The outer dense concrete skin incorporated 1/2-inch diameter, mild steel reinforcing bars which were laid horizontally at 2-foot vertical centres but the inner concrete skin was not reinforced.

The external walls were typically finished with a dense stone-dashed render coat to provide further protection from the elements and which was often painted over to provide an attractive finish.

Party walls were typically 8 inches thick and the partition walls of the ground and first floor 3 inches thick, both cast in non-reinforced clinker concrete. The suspended floors were typically fitted with timber joist and boards. The joist ends were covered in bituminous felt and supported in notches that had been cast in the inner skin of the external walls.

Houses Built after 1945

The Mk3 version which make-up the majority of houses, was modified to specification, and hence had cast in situ concrete walls, inner and outer leaves of 3 inches (7.6 cm) thickness separated by a 2 inches (5.1 cm) cavity, and reinforcement in both skins located in four horizontal bands above and below window openings.

The large proportion of Easiform houses still in existence today were built during this period. However several modifications were incorporated during this period compared to the pre-war examples.

The external cavity wall skins were thickened from 3 to 3 1/2 inches retaining the 2-inch cavity.

The inner and outer skins were both reinforced with steel rods encased in dense concrete strips, laid in four horizontal bands above and below window openings to provide increased strength.

The ground-floor partitions were typically cast using in-situ clinker concrete but the first-floor partitions were constructed using traditional breeze block.
Limestone quarry waste or Lytag replaced the typical clinker aggregate in some later builds and was used to construct the inner leaf and load bearing partitions. There are also examples of the external outer concrete leaf layer having been replaced with vertical hanging tiles or external brick skins, which can make identification of the build type difficult to the untrained eye.
Cavity Party walls, as expected, extend the full height of the dwelling with both inner and outer leaves constructed from clinker aggregate concrete.

THREE- AND FOUR-STOREY CONSTRUCTION
Post 1945, three- and four-storey blocks of Easi-form flats and maisonettes were constructed across the UK using a similar construction method to the post 1945 houses.

These properties do not not fit into a one type fits all approach as there were many variations incorporated into these builds, mainly in relation to strengthening the structure to accommodate significant load increases through additional storeys.

Some loadbearing walls were made thicker, floors alternated between reinforced concrete and traditional timber.
Some floors were constructed as solid in-situ slabs,, some employed lighter weight in-situ concrete ribs and hollow blocks which was sometimes overlaid with a structural layer of concrete.
Further reinforcements were made using reinforced concrete frames within the walls or increased use of reinforced steel, each with varying degrees of strength and success making it difficult for proper strength and integrity appraisal today.