Laing Easiform Cast-in-Situ House

The Easiform system of building is a cast-in-situ
concrete form of house construction developed by John Laing plc.
The first house was built in 1919, and approximately 5000 dwellings were completed during the interwar years, with most being erected in the mid-1920s. The Easiform system was reintroduced in 1946 and was in production until the early 1970s, providing a further 85,000 dwellings.

Since the walls are of cast-in-situ concrete the system is adaptable, giving many different plan configurations suited to varying types of accommodation. More than 25 basic types of Easiform houses, flats and maisonettes were produced, in two, three-and four-storey buildings, incorporating hipped and gabled roofs, porches of different designs, bay windows and brick outer cladding to the front and rear or side elevations.

The structural system of the Easiform house is essentially the same as that for a traditional cavity- walled brick dwelling. The floor and roof loads are taken directly to the foundations via the load bearing inner skin of the external walls, which in turn are stabilised and stiffened by wall tie connections to the outer skin.
The systems is simple and robust and can tolerate considerable damage without affecting the stability of the structure.
In addition, cast-in-situ cross walls provide substantial lateral bracing, and even in the unlikely event of partial failure of an external wall, damage to the rest of the structure would be limited.

Two storey Easiform constructions

Built during 1919 to mid-1920s
The very first Easiform houses have 8 inch thick solid concrete walls built with no-fines* clinker concrete, and approximately 2100 houses of this type were built before 1928. This report does not apply to this form of construction.

Built during mid-1920s to 1945
All cavity-walled Easiform construction is similar in that it has cast-in-situ concrete cavity construction for the external walls, not dissimilar to traditional cavity brick construction.
The outer skin of the cavity was cast with normal dense gravel aggregate and the inner skin was cast using clinker aggregate concrete. The two skins are connected with wall ties in the conventional manner.

In the first cavity-walled Easiform dwellings the two skins of the outer envelope are 3 inches thick and separated by a 2 -inch cavity. The outer dense concrete skin was specified with 1/2-inch diameter mild steel reinforcing bars placed horizontally at 2-foot vertical centres, whereas the inner clinker concrete skin had no reinforcement specified.
The outer skins of the external walls were usually finished with a dense stone-dashed render coat which has often subsequently been painted with a decorative finish.
The party walls are 8 inches thick and cast in clinker aggregate concrete, the partition walls to the ground floor and first floor are 3 inches thick, again cast in clinker aggregate concrete.
The suspended floors are usually of traditional timber joist/board construction and the ends of the joists are wrapped in bituminous felt and supported in notches cast in the inner skin of the external walls.
The rest of the construction is traditional.

Built after 1945
The majority of Easiform houses in existence today are of this later type, and differ in a number of respects from the pre-war dwellings. The thicknesses of the skins of the external cavity walls was increased from 3 inches to 3% inches with the 2-inch cavity retained. Reinforcement was specified both in the inner and outer skins and is grouped in four horizontal bands above and below window openings. Dense concrete strips encasing the reinforcement within the inner skin were also specified.

The ground-floor partitions were usually cast with in-situ clinker concrete, the first-floor partitions being provided in breeze block.
In some later dwellings, limestone quarry waste or Lytag was used instead of clinker aggregate in the inner leaf and load bearing partitions, and tile hanging or brickwork was sometimes substituted for the outer concrete leaf.
The party walls extend the full height of the dwellings and are of cavity construction similar to the external walls, except that both skins were cast using clinker aggregate concrete.
In other respects the construction is the same as that described for the earlier cavity-walled Easiform houses.

THREE- AND FOUR-STOREY CONSTRUCTION
After 1945, three- and four-storey blocks of flats and maisonettes were constructed. The form of construction is similar to that described in Section 2.3, except that some loadbearing walls may be thicker to accommodate the structural requirements, and alternate floors were sometimes constructed in reinforced concrete.
These floors may have been constructed using: solid in-situ slabs, in-situ ribs and hollow blocks, or occasionally precast ribs with hollow blocks with a structural topping.
Additional reinforcement was also incorporated in some developments to provide an in-situ reinforced concrete frame within the walls. In these circumstances there may be a considerable degree of redundancy in the structure and any appraisals should be carried out on the basis of the individual structure.

NOTES FOR SURVEYORS
(a) Since carbonation has usually occurred most rapidly from the cavity faces of the walls, if measurements of carbonation are required they should be made from cores taken through the complete thickness of the wall skins. The freshly fractured surface obtained by splitting the core longitudinally may then be sprayed with phenolphthalein solution in the usual way4.
(b) The original dense render coats, where used, are usually hard and well bonded to the concrete walls. Removal of this render may cause extensive damage to the outer skin of the concrete wall.
(c) Very small diameter reinforcement bars (2 to 3mm) may not cause cracking in the walls even in cases of severe corrosion.
CONCLUSIONS
(a) The cavity-walled Easiform houses have in general been constructed as designed, although variations in thicknesses of wall skins and types of reinforcement are common. These constructional variations have not affected the structural adequacy of the dwellings materially.
(b) Because three- and four-storey blocks may not be alike in their construction, they need to be appraised individually.
(c) The quality of concrete used throughout the Easiform system has not been sufficient to prevent carbonation from penetrating the walls down to the reinforcement. Carbonation to the depth of reinforcement may be expected to have
occurred in most Easiform properties over 30 years old.
(d) In the absence of chlorides, the rate of corrosion of reinforcement in the walls, once carbonation has reached the reinforcement, has been slow with approximately 10 to 15 years elapsing before corrosion sufficient to cause cracking has occurred.
(e) The onset of minor cracking has had no substantial effect on the stability or integrity of any of the dwellings inspected.
(f) After extensive and repeated cracking in some older houses (60 years old), larger movements and bowing have occurred in a few gable walls. In none of the cases inspected was the stability of the house in doubt.