EP0247050A1 - Composite building unit. - Google Patents

Abstract

A composite building element (10A, 21), having the configuration and overall dimensions of a standard brick, comprises an external enclosure (10A, 19) of brick clay filled with a core (21) of thermally cemented material. insulation which is welded to fired clay. When this element is used with other similar elements for the construction of a wall, it makes it possible to obtain an improvement in the thermal insulation index of the wall, as well as to realize savings in terms of costs and labor, especially when it is desired to make a facing with exposed bricks on the internal surface of the wall. In variants of the invention, the core (21) may consist of alternating layers parallel to one face of the visible element, made of a high density cementitious material supporting the charges and a cellular or crosslinked cementitious material. Alternatively, or as a complement, a thermal barrier can coat the interior of the enclosure (10A) in the cement core (21). In other variants the enclosure (10A) does not extend under the element and may include only one end or one side of the element. Instead of a ceramic material, the enclosure (10A) can be composed of a vitreous material or of natural or synthetic stone.

Description

TITLE:

"COMPOSITE BUILDING UNIT"

This invention relates to a composite building unit, and more particularly to a polyhedral composite building unit for laying with other, similar units in the construction of a wall. Architects and builders are nowadays confronted with increasing problems. Their customers are on the one hand conservative in their taste, having a preference for walls made from traditional materials such as brick or stone but on the other hand overridlngly cost conscious. Additionally, different countries apply progressively more stringent building regulations both to ensure safety and, with an increasing awareness of the need for energy conservation, especially in the colder climates of the more industrially advanced countries, the inhibition of heat transmittance across external walls of a building primarily to avoid heat loss from building interiors.

A common way to achieve heat insulation is cavity wall construction. In the case of an external wall of porous material, such as relatively low-grade, common brick the βavity serves the additional and more important purpose of preventing water ingress. When the external brick wall becomes saturated the cavity acts as a vapour barrier. Thus to a eertain extent measures which are adopted to increase heat insulation after a building has been constructed, such as filling the cavity with a settable, heat insulating foam, can be counter-productive. These measures have in any event come into disrepute. Poisonous or noxious emission into the building interior can occur when certain foams are used. On occasions the interior surface of an external wall must have a "fair facing", i.e. must be more aesthetically acceptable than, e.g. exposed brieze block or concrete. A cavity wall consisting of two leaves or skins of brick without plaster or other lining would present a fair-faced interior. A brick interior is often specified by the Client, but the standard 105 mm brick used to build two walls with a 50 mm cavity or spacing would not comply with e.g. British building regulations, which require a heat transmittance value across the wall (hereinafter referred to as the "μ value") of less than 0.6 w/m² deg. C. This value could be achieved by additional measures, such as building with one of the walls a heat insulating or reflective layer adjacent one of the inwardly presented faces of the two brick walls, but any such measures would be highly labour intensive and therefore prohibitively expensive. The alternative of providing either or both of the outwardly presented faces of the two brick walls with a suitable layer would also be expensive and, more to the point, would destroy the intended aesthetic effect.

The internal leaf or skin of a cavity wall is more commonly provided by building it not out of brick but by laying brieze blocks or blocks of thermally insulating concrete. These are cheap to produce and blocks of substantial thickness can be used because the material is relatively light in weight. The required μ value is easily achieved, but such inner walls certainly are not aesthetically acceptable, so that subsequent rendering or plastering or some other form of lining is in almost all cases essential. Alternatively a cavity wall which will have the required μ value may be constructed with an inner leaf or skin consisting of a timber frame supporting a thermal insulation material, say 100 mm thick. This however will require a finish or lining of plasterboard.

To achieve the required μ value it is not essential to provide a cavity at all. A single-leaf wall constructed from 150 mm blocks of thermally insulating concrete lined internally e.g. with vermiculite plaster or a dry lining could comply with building regulations but it is rarely used in the construction of habitable dwellings in oool climates. It would require a weather- and water-proof external render. The application of such a render would involve high labour costs and the finished building, having an unfamiliar appearance, would not on the whole be acceptable to conservative customers or planning authorities.

It will be seen, therefore, that when the customer specifies a brick interior additional measures have to be adopted to comply wϊh building regulations. Either an insulating layer e.g. of fibrous material must be built up in the cavity adjacent the inner brick leaf or skin or the thickness of the inner brick leaf or skin must be "artificially" increased, e.g. by building a layer of 50 mm brick bats adjacent the inner brick skin (leaving, of course, a cavity of about 50 mm between the brick bat wall and the outer brick skin). Both of these measures axe highly labour intensive and moreover the latter, at least, requires brick laying skills of a high order, leading to greatly increased costs. A principal object of the present invention is to provide a composite unit which, when built using traditional brick-laying techniques into a wall, will present exteriorly of at least one face of the wall the appearance of a conventional wall but which, because it has better heat insulating characteristics than conventional "fair facing" materials will not require special, additional measures to achieve the necessary μ value for a two-leaf or double skin cavity wall presenting a fair-faced internal surface.

Preferably the unit will have the shape and dimensions of a conventional brick or stone block so that it can be used without special instruction or training by anyone capable of bricklaying. This will particularly be the case if, as in preferred embodiments of the invention, both sides and both end faces of the unit axe of fired clay. In this event the bricklayer need not exercise any thought to ensure that both surfaces of the wall are wholly of brick appearance, even if courses of the wall include "end on" or "header" units.

It is not envisaged that the production of the units will be appreciably more expensive than the production of all-clay bricks, but even if the units themselves axe more expensive than traditional bricks their use instead of bricks will, as explained above, eliminate the need for expensive, labour-intensive thermal insulation or "wet trade" operations and thus greatly reduce the overall cost of a building (bearing in mind that labour represents a much greater proportion of overall cost than materials and, for example, that plasterers are more highly paid than bricklayers). There is believed to be scope for a considerable increase in cost per unit while still achieving a considerable reduction in overall cost.

Measures have previously been proposed for improving the thermal insulation characteristics of concrete blocks. For example, British Patent Specifications Nos. 1 252562 and 1 525 238 propose filled and/or open cavities in such blocks. It is also known to provide apertures in bricks - an airbrick is one obvious example. However, although the adhesion of cement to brick in a phenomenon well known in the building industry for hundreds if not thousands of years (being the basis, for example, of plastering or rendering) it has not, to the Applicant's knowledge, been exploited to provide a substitute for a brick which, while having the external appearance and advantages of a brick, will additionally have the advantages of a thermal concrete block. Apart from better thermal insulation characteristics these advantages axe potentially manifold. Unlike the "fixed" nature of brick clay once it has been selected - cementitious materials can be given a awide range of desired characteristics simply by altering the mixture or providing suitable inclusions. If mutually incompatible characteristics (e.g. high heat insulation and high load-bearing) are demanded of the same unit the problem can be solved by the use of layers of different cementitious mixtures all, ofcourse hydraulically and mechanisally bonded together and to the "fair faced" external surface(s) of the unit.

In one aspect, therefore, the present invention provides a polyhedral building unit for laying with other, similar units in the construction of a wall, the unit having load-bearing top and bottom surfaces and opposite side or end faces which will be exposed when the wall is constructed, characterised in that the unit is a composite wherein at least one of said faces forms part of an enclosure of ceramic or vitreous material or natural or synthetic stone, which enclosure contains and is cemented to a body of cementitious material, the body having lower thermal transmission characteristics than the material of the enclosure.

Examples of ceramic materials are fired brick clay or diatomaceous earth. By a vitreous material is primarily meant glass or a glassy substance which is used, in building, either to admit light or for ornamental effects. The enclosure could be constructed by mortarring or otherwise fixing together pieces of fired brick or stone or it may be made by moulding wet clay or a synthetic stone material to the required shape and firing it or allowing it to harden before bonding it to the cementitious body. Within all these variables the intention is to provide a unit which, exteriorly of the wall into which it is built, will present the appearance of a traditional building material and yet will provide thermal insulation characteristics for the wall superior to those of such traditional materials.

The improved thermal insulation characteristics of the cementitious body can be achieved solely by the selection of suitable inclusions for the mixture, or by giving it a layered construction of different cementitious mixtures selected respectively for load-bearing and for thermal insulation characteristics.

Alternatively, or in addition, thermal barriers may be included in the body, integrated with the adjacent cementitious material(s) by hydraulic and mechanical bonding. Where these barriers span the body between opposite sides or ends they will be arranged generally parallel with the face(s) of the unit which will be exposed from the constructed wall. For example, if the unit has the overall shape and dimensions of a conventional brick longitudinal thermal barriers may be included in units intended as "facers" and transverse thermal barriers may be included in "headers".

In the case of "glass bricks" (i.e. units in which the enclosure is of a transparent or translucent material) colourants can be added both to the vitreous material and to the cementitious mixture to produce desired ornamental or practical effects. In accordance with another aspect of the present invention there is provided a method of manufacturing the unit defined in Four the three immediately preceding paragraphs, the method comprising prefabricating an enclosure of ceramic or vitreous material or naturalor synthetic stone, placing the enclosure in a mould having an internal shape corresponding to the intended external shape of the unit and introducing into the mould a cementitious mixture capable of bonding hydraulically and mechanically to the material of the enclosure.

Different cementitious mixtures may be introduced into different areas of the mould so as to produce a layered but unitary cementitious body, all the layers being generally parallel with said at least one face of the finished unit, the layers mutually differing in load-bearing strength and thermal insulation characteristics. This layering of the body can be achieved either by prefabricating the layers and positioning them in the mould cementitiously to bond to adjacent layers or to the enclosure or by sub-dividing the interior of the mould with removable partition means and introducing different mixtures on opposite sides of the partitions. The partitions may either be physically bodily removed after serving their purpose or may be of a degradeable material which will not prevent bonding of one layer to another. Alternatively, or in addition, one or more thermal barriers may be prefabricated and inserted into the mould, cementitious material subsequently being introduced into the mould on opposite sides of the or each thermal barrier. In preferred constructions the or each thermal barrier comprises air- or gas-filled spaces. When more than one such thermal barrier is used it is preferably ensured that the spaces of adjacent barriers are not in alignment in a direction perpendicular to said one face of the unit. In the case of a unit with a vitreous enclosure the or each thermal barrier may be prefabricated from a similar material and inserted in the enclosure while both components are heat softened so that opposite ends of the barrier(s) fuse in position.

Preferred embodiments of the invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which: Figure 1 is an isometric view of a composite building unit in accordance with the invention,

Figure 2 is a cross-sectional elevation taken on the line II-II of Figure 1,

Figure 3 is an isometric view of the enclosure component (only) of an alternative unit in accordance with the invention, Figure 4 illustrates an optional additional step in the construction of the enclosure component of Figure 3,

Figure 5 is a sectional elevation of a completed unit having the enclosure component of Figure 4,

Figure 6 is a sectional elevation showing the component of Figure 4 positioned in a mould, Figure 7 diagrammatically illustrates the use of thermal barriers in an enclosure component similar to that of Figure 3. and

Figure 8 is a sectional elevation, on a larger scale, of one of the thermal barriers of Figure 7.

As shown in Figures 1 and 2 a composite unit is provided which has the overall shape and dimensions of a conventional house brick and which may be used in the same way in the construction of a wall, i.e. it may be laid with other, similar units, with or without the interposition of mortar, according to established brick-laying techniques. Unlike a conventional house brick, however, the unit does not consist entirely of clay. Similarly, unlike a conventional ooncrete block it does not consist entirely of concrete. By contrast it is made up of two components: (a) a box-like enclosure 10 the base 18 of which constitutes one of the longer sides 38 of the unit and (b) a body 11 of cementitious material contained by and hydraulically and mechanically bonded to the enclosures 10.

The principal purpose of the enclosure 10 is to give to the unit, when included in a wall, the appearance of a traditional building material and for this reason it is prefabricated from a ceramic material, such as fired clay, from a vitreous material, such as glass, or from natural or synthetic stone. The box-like shape can be achieved by building the enclosure 10 from separate pieces e.g. of stone or fired clay or by moulding wet clay, heat softened glass or a synthetic stone mixture to the shape illustrated prior to firing, hardening or setting.

However it is prefabricated the enclosure 10 preferably has inwardly directed lips or flanges 16 at the free end edges of its four "walls" such as 12 and 14. For additional anchorage to the cementitious body 11 additional flanges, ribs or protrusions such as indicated in phantom lines at 17 in Figure 2 may be formed or provided on inner surfaces of the enclosure component 10. After its prefabrication the component 10 is placed in a mould (not shown in figures 1 and 2) the internal shape of which is the intended external shape of the finished unit. A cementitious mixture together with a measured quantity of water is introduced into the mould so as to form the body 11, which will be hydxaulically and mechanically bonded (cemented) to the internal surfaces of the enclosure 10, providing an integral unit 10,11 at least one face 18 of which is of a "fair facing" material.

To provide the unit thus formed with better heat insulating characteristics than a unitary body of the same material as the enclosure component 10 the cementitious mixture of the body 11 has suitable inclusions such as expanded polystyrene granules, expanded clay, fibreglass, exfoliated vermiculite and/or expanded perlite. Known technology for the production of aerated concrete may be exploited to ensure that, in addition to strength-imparting aggregates, the cementitious material contains air- or gas-filled voids to provide improved thermal insulation. For example 0.2% by weight of aluminium powder may be included in the mixture. This will react with alkaline substances in the mixture to produce hydrogen bubbles before the mixture hardens. Thus a unit is provided with has load-bearing top 36 and bottom 37 surfaces, "facer" sides 38 and 39 and "header" ends 40 and 41. By suitably filling the mould with the cementitious material the external surfaces of the "sides" of the"box" 10 are flush with the exposed surfaces of the body 11 to give a regular, rectangular contour.

It will be apparent that alternative units may be constructed for use as "headers" in which the box-like enclosure 10 contains not one side but one end, such as 40 or 41, of the body 11. The brick layer ensures that in the construction of a wall all the units are positioned with the "fair facing" side or end, such as 18, presented outwardly in the same direction.

An alternative unit constructed using an enclosure 10A such as illustrated in Figures 3 - 7 does not require the brick-layer to exercise any thought as to which way round to place the unit, and the unit can equally be used either as a "facer" or as a "header". Figure 3 illustrates an annular enclosure 10A made by moulding or e.g. by bending a strip of wet clay about three transverse lines and then joining the ends. Optionally, and as illustrated in Figures 4, 5 and 6 the enclosure component 10A is given a base 19 of the same material. If made of clay the constructed component 10A may be fired in a kiln before being filled with a cementitious core 21 as shown in Figure 5. This

Figure also shows that weep-holes 20 may be provided in the base 19 for theescape of surplus moisture from the cementitious core 21.

The choice of materials for the enclosure 10A, with or without a base 19, and for the cementitious core 21, is as indicated in connection with the embodiment of Figures 1 and 2. Preferably, and as shown in Figure 6, the prefabricated and hardened enclosure component 10A is placed in a cast-iron mould 23 before the introduction of the cementitious mixture. In the case of clay for the component 10A it may be fired while in the mould 23, the mould being covered by a removable lid 24 having perforations 26. The mould 23 may serve the secondary purpose of supporting the component 10A while a cementitious core 21 is formed therein. This will be particularly advantageous if, for example, polystyrene granules or other thermal insulation inclusions axe introduced under pressure into the cementitious mixture before it has hardened and before it has bonded to the enclosure 10A or if it is desired to impart vibration to the unit during the introduction of the cementitious mixture, e.g. to Impart improved load-bearing properties to the core 21. Although in Figure 5 the core 21 is shown as a homogeneous body it may alternatively be constructed from mutually bonded, adjacent layers all of cementitious material but differing in their load-bearing and thermal insulation characteristics. Thus certain layers may provide the unit with the requisite load-bearing strength, being of a dense, high-aggregate mixture while one or more other layers may be reticulated or consist of a high proportion of air- or gas-filled voids. Where layers provided for their thermal insulation characteristics span the length of the core 21 between the end walls 40 and 41 of the unit, or alternatively the width of the core 21 between the sidewalls 38 and 39 of the unit, it is desirable that they should be generally parallel to the sides, or to the ends, of the unit, i.e. that any thermally insulating layer should be perpendicular to the direction in which the unit will face outward of a wall, in use.

Individual layers may be prefabricated separately, e.g. by moulding, before introduction into the enclosure 10A or alternatively the interior of the enclosure 10A may be sub-divided by removable partition means (not shown) and the cementitious mixtures introduced on opposite sides of the partitions. The removable partition means may be physically removable before the wetted cementitious mixtures have hardened, allowing them to bond together, or degradable or porous membrane partition means may be used which, while serving to separate the dry mixtures when introduced so as generally to preserve the shape of the layers, will not prevent the wetted mixtures from bonding together. Figures 7 and 8 illustrate a further modification of the unit in accordance with the invention in which prefabricated thermal barrier elements 50A and 50B are positioned in the enclosure 10A, and their end edges fixed to the end walls 40 and 41 of the enclosure 10A, before cementitious material is introduced on opposite sides of each barrier element 50A and 50B. As shown in Figure 8 each barrier element such as 50A may itself be of cementitious material. A base member 51 is made, for example by moulding, from an aerated cementitious mixture so as to have recesses 52 distributed throughout one face. Subsequently a membrane 53 Is laid over this face and covered by another cementitious layer 54 so as to form a barrier element 50A a high proportion of the interior of which is made up of voids because the membrane 52 has prevented the added layer 54 filling the recesses 52. Subsequent to prefabricating the enclosure 10A arid the barrier elements 50A and 50B, e.g. in separate moulds, the barrier elements 50A and 50B are inserted into the enclosure component 10A so that their opposite edges bond to the end walls 40 and 41. Of course if both components 10A and 50A or 50B axe dry at this stage it may be necessary to use additional cement. Subsequent to the positioning of the barrier elements 50A and 50B In the enclosure 10A cementitious material is introduced on opposite sides of each barrier element 50A and 50B, as in the previous examples, to bond both to the barrier elements and to the interior surfaces of the enclosure 10A.

In a mass production process the two barrier elements 50A and 50B would differ in the disposition along their lengths and/or breadths of the voids 52 therein so that, in a direction perpendicular to the sides 38 and 39 of the unit, no two voids of the respective barrier elements 50A and 50B would be in alignment. Both the enclosure 10A and the barrier elements 50A and 50B may be made of glass, e.g. by moulding, in which case the barrier elements 50A and 50B may be inserted in the enclosure 10A while the glass is still hot so 'that the end edges of the Barriers will fuse to the enclosure. After allowing the assembly to cool it is filled with a cementitious mixture, and in this case the mixture(s) may include suitable colourant(s).

Although primarily intended as a substitute for a standard brick and as such of similar overall shape and dimensions larger units (e.g. 150 mm x 215 mm) may be provided for particular purposes, for example to build an external wall with a ceramic facing in a building of timberframe construction. In this case additional insulation between the studwork may be dispensed with if the units of the invention are given adequate thermal insulation properties.

Claims

CLAIMS:

1. A polyhedral building unit for laying with other, similar units in the construction of a wall, the unit having load-bearing top (26) and bottom (37) surfaces and opposite side (38,39) or end (40,41) faces which will be exposed when the wall is constructed, characterised in that the unit (10,11)(10A,21) is a composite wherein at least one (18) of said faces forms part of an enclosure (10,10A) of eeramic or vitreous material or natural or synthetic stone, which enclosure (10,10A) contains and is cemented to a body (11,21) of cementitious material, the body (11,21) having lower thermal transmission characteristics per unit area and in a given direction than the material of the enclosure (10.10A).

2. A unit as claimed in claim 1 characterised in that the body (11,21) comprises a thermally insulating cementitious material.

3. A unit as claimed in claim 2 characterised in that the cementitious material is aerated.

4. A unit as claimed in claim 3, characterised in that the cementitious material is aerated by the inclusion of polystyrene granules.

5. A unit as claimed in claim 3, characterised in that the cementitious material comprises expanded clay.

6. A unit as claimed in any one of the preceding claims, characterised in that the body (11,21) comprises exfoliated vermiculite.

7. A unit as claimed in any one of the preceding claims, characterised in that the body (11,21) comprises expanded perlite.

8. A unit as claimed in any one of the preceding claims, characterised in that the body (11,21) comprises a cementitious mixture including fibreglass.

9. A unit as claimed in any one of the preceding claims, characterised in that there is included in the body (11,21) at least one thermal barrier layer (50A,50B) generally parallel with said face (18).

10. A unit as claimed in claim 9, characterised in that the thermal barrier layer (50A,50B) comprises discrete, air- or gas-filled voids (52) distributed throughout its length and breadth.

11. A unit as claimed in claim 9 or claim 10, characterised by the provision of a plurality of thermal barrier layers (50A.50B) in mutually spaced relation within the body (11,21) and each generally parallel with said face (18).

12. A unit as claimed in claim 11 as appendant to claim 10, characterised in that the voids (52) of one barrier (50A,50B) are not aligned in a direction perpendicular to said face (18) with the voids (52) of an adjacent barrier (50A.50B).

13. A unit as claimed in any one of claims 9 to 12, characterised in that the or each said thermal barrier layer is a prefabricated unit (50A,50B) comprising a base (51) formed in oie face thereof with a plurality of recesses (52) and a covering element (54) extending over said one face of the base (51) without filling the recesses (52) but serving to seal the same.

14. A unit as claimed in claim 13, characterised in that the base (51) is moulded from aerated cementitious material and the covering element (54) is of cementitious material.

15. A unit as claimed in claim 14, characterised in that a degradable membrane (53) Is interposed between the base (51) and the covering element (54) to prevent the material of the latter filling the recesses (52) of the base (51) before the cementitious material has hardened.

16. A unit as claimed in claim 9, characterised in that the or each said thermal barrier layer (50A,50B) is of a vitreous material such as glass.

17. A method of manufacturing the unit claimed in claim 1, characterised in that the method comprises prefabricating an enclosure (10,10A) of ceramic or vitreous material or natural or synthetic stone, placing the enclosure (10,10A) in a mould (23) having an internal shape corresponding to the intended external shape of the unit (10,11)(10A,21) and introducing into the mould a cementitious mixture capable of bonding hydraulically and mechanically to the material of the enclosure (10,10A).

18. A method as claimed in claim 17, characterised in that the cementitious mixture includes fibreglass.

19. A method as claimed in claim 17, characterised in that the cementitious mixture includes polystyrene granules.

20. A method as claimed in claim 17, characterised in that the cementitious mixture includes expanded clay.

21. A method as claimed in claim 17, characterised in that the cementitious mixture includes exfoliated vermiculite.

22. A method as claimed in claim 17, characterised in that the cementitious mixture includes expanded perlite.

23. A method as claimed in any of claims 17 to 22, characterised in that different cementitious mixtures axe intxoduced into different areas of the mould so as to produce a layered but unitary cementitious body (21), all the layers being generally parallel with said at least one face (18) of the finished unit, the layers mutually differing in load-bearing strength and thermal insulation characteristics.

24. A method as claimed in any one of claims 17 to 23, characterised in that the enclosure (10A) is annular and is arranged around side-walls of the mould (23) so that the cementitious mixture, when introduced into the mould (23) forms a core (21) surrounded by the enclosure (10A).

25. A method as claimed in claim 24 characterised by the further step of separately prefabricating one or more thermal barriers

(50A.50B), inserting the or each thermal barrier (50A,50B) into the enclosure (10A) within the mould (23) so that the or each thermal barrier (50A,50B) spans the space between two opposed side- or end-walls of the enclosure (10A) in spaced relation to the other two opposed end- or side-walls of the enclosure (10A) and subsequently introducing the cementitious mixtureinto the enclosure (10A) on opposite sides of the or each thermal barrier (50A,50B).

26. A method as claimed in claim 25, characterised in that the or each thermal barrier (50A,50B) is prefabricated by moulding a base (51) to have recesses (52) in one face thereof and covering said one face with a cover element (54) to seal but not fill the recesses (52).

27. A method as claimed in claim 25 or claim 26, characterised in that both the enclosure (10A) and the or each thermal barrier

(50A,50B) are of a vitreous material such as glass and in that the or each thermal barrier (50A,50B) is inserted in the enclosure (10A) after the latter has been positioned in the mould (23) but while both the enclosure (10A) and the or each thermal barrier (50A,50B) axe in a heat-softened condition such that opposite ends of the the or each thermal barrier (50A,50B) fuse to opposite sides or ends of the enclosure (10A), and in that the assembly of the enclosure (10A) and thermal barrier or barriers (50A,50B) are allowed to cool before the introduction of the cementitious mixture.

28. A method as claimed in any one of claims 17 to 27, characterised in that the enclosure (10A) is prefabricated from fired clay before introduction of the cementitious material.

29. A method as claimed in claim 28 as appendant to claim 25, characterised in that the base (51) and the cover element (54) of the or each thermal barrier (50A.50B) are prefabricated from cementitious material and in that the or each thermal barrier (50A,50B) is cemented into position within the enclosure (10A) before the introduction of said cementitious mixture on opposite sides of the or each thermal barrier (50A,50B).