CORRUGATED OR RIBBED ROOFING SHEETS OF SYNTHETIC FIBRE-REINFORCED CEMENT, WITH A ROUGH SURFACE DUE TO THE PRESENCE OF GRANULAR MATERIAL

Abstract: Corrugated or ribbed roofing sheets for buildings, consisting of a mixture of cement and inerts reinforced with synthetic fibres either in fibrillated mesh form or not, characterised by having a rough outer surface due to the presence of surface granular material. Said granular material is applied to the sheets during their finishing but before the cement has started to set, by simply strewing it over the sheet surface.

Description: Granular material is of known use in building components such as insulating sheets (FR-A-2248384). Concrete components in the form of sheets with a rough surface and a vapour-impermeable film are also known (DE-A-3022266), as are asbestos-cement sheets with granular material applied by pressing onto the surface of a cement layer superposed on the asbestos-cement (JP-A-53144926). In addition asbestos-cement board, siding and shingle having incorporated finely ground mineral oxide pigments, inorganic or organic pigments, phthalocyanine pulp pigments, dyes, lakes or other coloring matter are known (US-A- 2 818 824). However, synthetic fibre-reinforced cement sheets with a rough surface having non-slip characteristics for roofing use in buildings are as yet unknown. We have now found it possible to produce corrugated or ribbed roofing sheets for buildings consisting essentially of a cement and inerts mixture reinforced with synthetic fibres either in fibrillated mesh form or not, which have a rough outer surface due to the presence of surface granular material applied by simple strewing. Said sheets are produced in known continuously operating plants, by: a) preparing a suitable thickness layer of a mix of cement with sand and other inert materials, and containing synthetic fibres in the form of fibrillated meshes or not, by either spraying the mix of cement and inerts or allowing it to fall onto a felt or cloth band which advances continuously while supporting the fibre layer to be impregnated; b) strewing granular material over the surface of said layer before the cement starts to set; c) removing excess water from said layer by fixed or mobile suction boxes; d) after the cement has set, brushing to remove from the surface those granules which have not been gripped by the cement. The sheets of the present invention have functional and aesthetic characteristics which represent a considerable advance over components of the known art used for the same purpose, and their production cycle has advantageous aspects. This invention relates to corrugated or ribbed roofing sheets for buildings, and the method for their production. Said sheets consist of a cement and inerts mixture reinforced with synthetic fibres, and are characterised by possessing a rough outer surface due to the presence of surface granular material. Said synthetic fibres are preferably polypropylene fibres in the form of a fibrillated mesh or not, and have a much larger diameter than the asbestos fibres traditionally used in this field, namely between 15 and 120 microns compared with the generally between 1 and 3 micron diameter of asbestos fibres. The granular material used for roughening the surface of the sheets according to the present invention is grit produced from mineral substances such as limestone, marble, silica, granite etc. by grinding the sieving to a particle size of between 0.1 and 4 mm and preferably between 0.5 and 1.5 mm. Said material can also consist of glass beads of the same size. Said granular material is applied to the sheet surface in a quantity of between 200 and 1500 g/m² and preferably between 500 and 1000 g/m². Said material is applied by distributing the granular material over the surface of the sheets during their finishing and before the cement has started to set. Thus, a layer of mix containing synthetic fibres is prepared to a thickness suitable for the sheet to be produced. The synthetic fibres are present to the extent of between 2.0 and 3.5% of the remaining solid material by weight. Said layer is prepared using a plant comprising a continuously advancing felt or cloth band on which the layer is deposited by free fall or spraying, so engaging the fibres which have been previously deposited. The layer surface consists essentially of cement, sand and any other additives, the synthetic fibres remaining well distanced apart and embedded in the mass as they are both thick and spread out. As the sheet advances it is subjected to known finishing operations such as smoothing. At this point the granular material is strewn over the sheet surface, consisting essentially of wet cement and any inert additives, before the cement has started to set, after which the normal operations are continued such as removing any excess water by suction boxes, cutting and corrugating, placing on steel forms and stacking. Specifically, water removal is continued until the residual water content is between 25 and 32% and preferably between 27 and 29% of the weight. As the cement sets it grips the granules with which it comes into contact, and when the cement is completely set the sheet surface is brushed to remove those material granules which have not been gripped by the cement. The sheet corrugation or ribbing profiles can be one of the known range corresponding for example to UNI 3949 177/6 or 146, ISO 691 or 692, or a different standard. The sheets according to the invention have production, functional and aesthetic advantages compared with the known art. Their production process has firstly the advantage of comprising a simple and economical method of applying the granular material. A further advantage is the following: the corrugated or ribbed sheets must be stacked with interposed plate steel forms between one sheet and the next in order to keep the shape of each sheet unaltered during the setting of the cement. During this operation, if the synthetic fibre-reinforced sheets were not covered with granular material they would become scratched and marked at their points of contact with the plate steel forms, so that their final appearance would be deteriorated. This defect is inherent in components consisting of a synthetic fibre-reinforced mixture of cement and inerts because their surface consists essentially of cement. This does not however happen in the case of asbestos-cement as the asbestos reaches the surface to protect it from scratching. In the case of synthetic fibre-reinforced sheets without asbestos, the presence of the granular material makes the sheet surface insensitive to the action of the plate steel forms, so that the sheets according to the invention preserve a perfect surface. The sheets according to the invention also have the following advantageous characteristics from the functional aspect: when used directly as roofing sheets they obstruct the slippage of snow by virtue of the increased friction determined by the surface granular material; when used as tile support sheets in which when the roof is finished their surface is not visible because it is covered by the tiles for which they act as a support, the increased friction between the sheet and tile prevents this latter slipping downwards. Furthermore if the tiles are fixed by mortar for example to resist the underthrust of the wind, the mortar adheres better to the rough surface of the sheet so that the fixing is more secure; in the case of only slightly inclined pitches, where the horizontal superimposed parts have to be sealed with mastic, the mastic is more easily retained by the rough surface, and consequently the seal lasts longer as it better resists the small to-an-fro movements which the roof undergoes due to temperature and humidity variations; there is a reduced risk of slippage of the load distribution boards which maintenance personnel lay on the roof when walking on it, or of slippage of the actual personnel if treading directly on the roof; in drilling the sheets to take the screws or nails used to fix the ridge tiles, the time loss due to easy lateral slippage of the drill bit on commencing drilling is avoided because when the drill bit touches the surface to be drilled, the roughness produces an initial guide sufficient to retain the bit in the required drilling position. From the aesthetic aspect the sheets have the following advantageous characteristics: absence of undesirable reflection by virtue of a non-shiny surface; better colour uniformity due to the absence of reflection; regular and uniform ageing of the surface, the appearance of which always remains uniform with time because the film which forms with age adheres uniformly to every point by virtue of the considerable surface roughness.

Claims: Corrugated or ribbed roofing sheets consisting of cement reinforced with synthetic fibres either in fibrillated mesh form or not, the sheets having a rough surface due to the presence of surface granular material consisting of mineral substances ground and sieved to a particle size of between 0.1 and 4 mm and preferably between 0.5 and 1.5 mm. Sheets as claimed in claim 1, characterised in that said granular material consists of limestone, marble, silica or granite. Sheets as claimed in claim 1, characterised in that said granular material is applied to said surface in a quantity of between 200 and 1500 g/m² and preferably between 500 and 1000 g/m². A method for producing sheets claimed in claims 1 to 3, comprising: a) preparing a suitable thickness layer of a mix of cement and inert materials, and containing synthetic fibres in the form of fibrillated mesh or not, by either spraying the mix or allowing it to fall onto a felt or cloth band which advances continuously while supporting the fibre layer to be impregnated; b) strewing granular material over the surface of said layer before the cement starts to set; c) removing excess water from said layer by fixed or mobile suction boxes; d) after the cement has set, brushing to remove from the surface those granules which have not been gripped by the cement. A method as claimed in claim 4, characterised in that the content of said synthetic fibres is between 2.0 and 3.5% by weight of the remaining solid material. A method as claimed in claim 4, characterised in that said synthetic fibres are polypropylene fibres. A method as claimed in claim 4, characterised in that said synthetic fibres have a diameter of between 15 and 120 microns. A method as claimed in claim 4, characterised in that said water removal is continued until its residual content is between 25 and 32% by weight.

Inventors: MAGNANI, SILVIO
Applicants: S.I.D.I.-SOCIETE INTERNATIONALE DE DEVELOPPEMENTS INDUSTRIELS S.A. HOLDING
Application year: 1988
Main classification: E04D3
IPC codes: E04C5, E04D3