GB2275940A

GB2275940A - An arch former

Info

Publication number: GB2275940A
Application number: GB9305075A
Authority: GB
Inventors: Philip Thomas Corkill; Jeffrey David Adams
Original assignee: P T CORKILL Ltd
Current assignee: P T CORKILL Ltd
Priority date: 1993-03-12
Filing date: 1993-03-12
Publication date: 1994-09-14
Anticipated expiration: 2013-03-12
Also published as: GB9305075D0; GB2275940B

Abstract

The present invention concerns an arch former comprising a soffit portion (10) having a fully finished surface supported by side walls (12) and (13), which are preferably spaced apart, the space therebetween being preferably filled with a fire resistant polystyrene foam. The arch former may be readily attached by appropriate fixing means to the internal surface of a square arch opening, for example by screwing or nailing such to the existing walls and ceilings. The side wall portions are inset at a desired depth according to whether or not such are intended to receive a skim coat or full depth plaster, which in use can be skimmed to the finished edge provided by the preformed precast soffit portion (10). The side walls may be plaster, plasterboard, hardboard or metal mesh, and the plaster may be glass reinforced gypsum. <IMAGE>

Description

ARCH rORXER The present invention relates to an arch former for use in the construction of arched openings in buildings.

At present, in order to produce an arched opening in a building, a variety of techniques are used to produce an arch, utilising plywood, plasterboard, hardboard, or metal, or a combination of such materials and metal arch formers, which are constructed on site and to which plaster must then be applied in traditional manner to achieve a finished arch. Such techniques can be relatively laborious and time consuming and thereby relatively expensive. Furthermore, due to the relative difficulty in obtaining a smooth curve under such conditions, the finished product may not be a perfect curve, but merely a close approximation. Also, it is difficult to obtain a good edge at the corner of the soffit of the arch. Alternatively, finished archways are known which are precast in the solid from a casing plaster, which are merely positioned in the opening and secured. However, such cast archways are relatively expensive and also heavy and unsuitable for use in the construction of simple arch openings due to their cost and weight.

It is the object of the present invention to provide a low cost lightweight arch former which provides an easy and accurate method of forming arches for solid plaster work or dry lining.

According to the present invention there is provided an arch former comprising: a curved soffit portion of predetermined curvature and shape so as to form the interior curve of at least a portion of an arch having a finished surface; and support means for said soffit portion which extends from the rear of said soffit to form a corner, side walls of the support means being inset from the edges of the soffit.

Preferably, the side walls are inset slightly from the edge of the soffit portion to enable a skim coat of finishing plaster to be applied thereto in situ, the soffit thickness being sufficient to support a good finished edge for the plasterer to work to. If specified, the side walls could be inset more deeply to accommodate a full thickness of plaster.

The support means preferably comprises spaced-apart plaster walls cast integrally with the soffit portion, but such could comprise other materials capable of both supporting the soffit portion and accepting a finishing plaster or slurry. Plaster side walls should be of sufficient thickness to provide the necessary rigidity and support to the structure and may range from a minimum of approximately 6 mm up to, say, 20 mm, but are preferably 12 mm to provide the necessary fire retardant features. Further, the cavity between the supporting walls may be filled with a foamed material or expanded polystyrene or a suitable support structure, capable of providing the necessary rigidity and lightness in weight, so that the arch former is readily handleable in use without risk of significant damage thereto on site. Other materials which could be utilised to form the support means would include expanded metal mesh, or the like, plasterboard, or hardboard. Alternatively, the support means could be provided by a solid support member, possibly a composite plaster/polystyrene mixture, combining the desired robustness and lightness, whilst still capable of accepting finishing plaster.

In the preferred embodiment, the plaster utilised is preferably a medium grade casting plaster, although any suitable grade of casting plaster may be utilised according to specific requirements. In order to improve the strength and robustness of the casting plaster, it has been found preferable to incorporate a polymer modifier together with chopped strands of glass fiber to produce a glass reinforced gypsum, the combination of which improves the strength of the finished product. However, if higher grades of casting plaster are utilised, then it may not be necessary to utilise such additives to increase the strength.

The present invention will now be described further with reference to the accompanying drawings, in which: Fig. 1 is a top view of the arch former; Fig. 2 is a perspective view of the arch former; Fig. 3 is a section on the line A-A of Fig. 2; and Figs. 4a and 4b illustrate two styles of arch former in situ.

Referring to firstly Figs. 1, 2 and 3, the general design of the arch former can be seen, the shaping of the arch being provided by the soffit 10, the inward facing surface of which is a finished plaster surface requiring no additional plaster to be applied on site and the support structure for which comprises a support portion 11 from which extend a pair of spaced -apart wall portions 12 and 13. Between the spaced-apart wall portions 12 and 13, the space is filled with a fire resistant grade of expanded polystyrene, around which the arch former is preferably cast, which imparts necessary rigidity to the structure whilst maintaining the lightness. The walls 12 and 13 are preferably 12 mm thick, although this could be varied from between a minimum of approximately 6 mm and a maximum of approximately 20 mm, subject to maintaining the criteria of, on the one hand, retaining the necessary fire resistance, possibly by means of a suitable fire retardant filler, and, on the other hand, retaining the lightness of construction for ease of handling. Whilst a fire resistant grade of expanded polystyrene is the preferred filler, other suitable fillers could be utilised, subject to their meeting the criteria of fire resistance and lightness, or alternatively the spacing between the walls 12 and 13 could be left unfilled, in which case the wall thickness of the walls 12 and 13 may need to be increased and webs provided extending between the walls to provide the necessary rigidity. Alternatively, a preformed insert could be utilised which could be produced of a lightweight plastics material in the form of a honeycomb or box-like structure to give the combination of strength and lightness required.

The walls 12 and 13 are inset slightly from the external edge of the soffit portion 10 to provide a lip, of between lmm and 13mm, but preferably approximately 3 mm, to accommodate a finishing coat to be applied to the side walls in situ, whilst at the same time providing a finished edge for the arch itself.

The arch former may be secured in position by means of screws which can be located in pilot holes provided in the casting of the former, which may then be covered and skimmed over to conceal such in the finished arch. Additional fixing may be provided by adhesives along the top and side surfaces of the support portion.

Of course, the former could be simply nailed in position, but this is not recommended due to the risk of damage to the structure of the arch during fixing.

In order to accommodate the range of possible wall widths within which the arch may be located, such can be made in a range of sizes from a minimum of 50 mm rising to 450 mm and might suitably have a radius of say 380 mm, although a range of different radiussed castings could be provided to accommodate a variety of sizes of arch. Further, particularly in the case of an arch former incorporating an expanded polystyrene filler or core, the soffit width could be adjusted on site to accommodate non-standard wall widths by simply sawing through the arch former and removing a portion thereof and bonding such back together, which would of course require some dressing of the interior surface of the arch, but would retain the finished edges, which would not be effected by such process. Thus, it would simply be necessary for the user to purchase an oversize arch former and cut this to size on site. Due to the construction of the arch former, such can be readily sawn without damaging to any significant extent the integrity of the arch when such is bonded back together and located in place.

Thus, it can be seen from the above, the arrangement of the present invention provides a versatile lightweight and relatively cheap method of forming an arch which may even be suitable for use as a D.I.Y. product, having considerable advantages over prior art arrangements.

Examples of arches produced utilising such formers of different shapes and styles are shown in Figs. 4a and 4b.

Claims

1. An arch former comprising: a curved soffit portion of predetermined curvature and shape so as to form the interior curve of at least a portion of an arch and having a finished surface; and support means for said soffit portion which extends from the rear of said soft it portion to form a corner, side walls of the support means being inset from the edges of the soffit portion.

2. An arch former as claimed in claim 1 in which the side walls are inset sufficiently from the edge of the soffit portion to enable to skim coat of finishing plaster to be applied thereto.

3. An arch former as claimed in claim 1 in which the side walls are inset sufficiently for a full normal thickness of plaster to be applied thereto.

4. An arch former as claimed in any preceding claim in which the soffit portion is sufficiently thick to support a finished edge and is preferably substantially 10 mm thick.

5. An arch former as claimed in any preceding claim wherein said support means comprises spaced apart plaster wall portions cast integrally with the soffit portion.

6. An arch former as claimed in claim 5 in which the plaster side walls have a thickness of between 6 mm and 20 mm.

7. An arch former as claimed in claim 5 or 6 in which the plaster side walls are substantially 12 mm thick.

8. An arch former as claimed in any of claims 1 to 4 in which the support means comprises expanded metal mesh, plasterboard, or hardboard spaced-apart wall portions cast into the soffit portion.

9. An arch former as claimed in any of claims 5 to 8 in which the cavity between the side walls is filled with a foamed material or expanded polystyrene or receives a lightweight support structure.

10. An arch former as claimed in any of claims 1 to 4 in which the support means comprises a solid support member preferably of a plaster/polystyrene mixture of a suitable composition to provide lightness and robustness.

11. An arch former as claimed in any of claims 1 to 7 in which the plaster is a medium grade casting plaster.

12. An arch former as claimed in any of claims 1 to 7 in which the plaster utilised is glass reinforced gypsum which comprises a casting plaster together with a polymer modifier and chopped strands of glass fibre in a predetermined combination.

13. An arch former as claimed in any preceding claim in which the soffit portion forms a curve approximating a quarter circle.

14. An arch former as claimed in any of claims 1 to 12 in which the soffit portion includes a curved portion and at least one straight portion to provide for arches of different configuration.

15. An arch former substantially as hereinbefore described with reference to the accompanying drawings.