GB2053184A

GB2053184A - Plaster composition

Info

Publication number: GB2053184A
Application number: GB8016558A
Authority: GB
Original assignee: Stockton L W
Current assignee: Stockton L W
Priority date: 1979-05-22
Filing date: 1980-05-20
Publication date: 1981-02-04

Abstract

A composition comprises a water settable plaster, water, a polymeric material, and a fibrous reinforcing material. The polymeric material may be polyvinyl acetate, styrene butadienes, acrylics, polyesters, epoxies or other resinous or rubber band materials. Lightweight fillers or other fillers may be present.

Description

SPECIFICATION Improvements in or relating to gypsum plaster The invention relates to gypsum plaster and its principal object is to provide a novel composition employing gypsum plaster in combination with other organic and inorganic materials which would result in products which, in comparison with existing products, are either lighter or more flexible, or less brittle, or more water resistant, or easier to cut or nail, or having properties which are a combination of two or more of the above properties. It thus relates to substantial improvements on the existing compositions. The invention also relates to products made from the novel composition and to methods of making them.

The use of gypsum plaster has been known to the civilised world for the last few thousand years. The pyramids at Giza and the tombs of Saqqara are examples of early applications. Throughout the ages, use has been made of gypsum plaster for building, decorative, sculptural, medical and other purposes, taking advantage of some of the desirable properties. Some of the gypsum plasters (e.g. Plaster of Paris) set very rapidly when mixed with water - which is a useful property in some applications - but to make it usable for building work small quantities of Keratin or similar glue-like materials are added to retard the set. The material so produced is known as retarded hemihydrate plaster. The an hydros calcium sulphate on the other hand does not set and harden in a reasonable time and accelerators of various types have to be added.

This has resulted in the production of a number of proprietary brands of plaster, for example Keenes', Parian and Martin's.

Thus it will be seen that the gypsum plasters are available with varying degree of setting times. However the products made from plaster suffer from the following defects: (i) they are heavy in weight; (ii) they are rigid and lack that degree of flexibility which is desirable to fit in with the tolerances found in the building trade; (iii) they are highly brittle which results in a considerable amount of wastage; (iv) they are very weak in tension - this would put limitation on the size as well as usage, e.g.

(a) the length of the product will be limited as the product might crack under its own weight: (b) the products will be totally non-structural; (v) At present the products are liable to severe degradation resulting in loss of shape and strength when exposed to damp conditions and hence the existing products are only suitable for internal use; (vi) the setting time for most of the decorative plasterwork is very short, this therefore results in limitation of the size of the product and its ability for moulding or pattern making. In the past when expert pattern making plasterers were available many of the intricate designs were carried out by taking a small quantity of plaster, putting it on the ceiling or wall and working very swiftly on the plaster before it set.

Patterns and designs were also obtained. by carving or sculpture on hardening or hardened plaster. The process was therefore time consuming and the objects of art like churches, cathedrals and palaces took years to be decorated. In the present day and age we have neither those master plasterers nor the time to do the job by the methods they adopted; (vii) as mentioned earlier the poor tensile strength and brittle nature of the material resulted in incapability of the material to absorb stresses and shocks caused by cutting or nailing. Attempts to cut or nail the products therefore resulted in cracking, spalling, local and sometime total deformation or destruction of the products - thus further limiting its use.

Some of the defects mentioned above have been dealt with on an individual basis e.g. vermiculite has been added to the plaster to make it light weight and more workable, fibres have been added to improve tensile or impact strength. However, little or no attempt has been made to improve the properties or eliminate most of the defects so as to radically change the performance and usage of the products by adopting a novel composition consisting mainly of gypsum plaster and water in combination with other materials to eliminate its defects.

According to the present invention, the novel composition suitable for the manufacture therefrom of the improved product which may be highly patterned, decorated or could become part of an overall design, comprises: (i) a water-settable inorganic binder which is one or more of a calcium sulphate binder, Plaster of Paris, Retarded Hemihydrate plaster, Anhydrous Calcium Sulphate, Anhydrate or any of the propriatary brands of plaster; (ii) water; (iii) Polymers, and Copolymers which may be water dispersible e.g. polyvynyl acetates, styrene butadienes, acrylics, polyesters, epoxies, and other resinous or rubber based materials; (iv) fibrous reinforcing materials, comprising inorganic or organic fibres or combinations of both.

The composition preferably includes an aerating agent in the form of a light weight filler - e.g. expanded vermiculite, expanded perlite, sawdust, p.f.a. floaters, polystyrene beads and such other light-weight materials or any combination of the above materials.

The invention also provides a composition suitable for the manufacture of plain, patterned or decorative product comprising (i) compounds necessary for the formation of calcium sulphate binder; (ii) water; (iii) compounds necessary for the formation of liquid Polymer; (iv) fibrous reinforcing material comprising inorganic and/or organic fibres. An aerating agent or light weight filler is also preferably included.

The composition of the invention may be used in the manufacture of all kinds of shaped articles such as ceiling rose, coves, friezes, dado rails, cornices, fire-place surrounds, ceiling tiles, ceiling decorations, wall decorations, wall panels, door panels, boards, skirting boards, architraves, door casings, door heads, pilasters, decorative moulding strips, etc. The composition of the invention may also be used for medical orthopaedic plaster casts, busts, statues, decorative and artistic pieces for chess boards, draft boards, carrom boards etc.

Polymers and rubbers are preferably in liquid form and the suitable rubbers and polymers are those the use of which within the prescribed limit would impart flexibility and also increase tensile and/or impact resistance of the final product. The polymers may comprise 1% to 75% (preferably 1% to 30%) of the total weight of the composition. The solid content of the liquid polymer may comprise not less than 10% (preferably 40% to 60%) of the weight of the liquid polymer.

Polymer addition will also decrease the modulus of elasticity of the matrix and thus improve the efficiency of the reinforcing fibres, so that a lower concentration of fibres in the proposed matrices is as effective as a higherconcentration in normal plaster matrices.

The inclusion of the light weight filler material up to 49% of the total weight of the solids (i.e. binder, fibres, and light weight filler if any) will help to reduce the weight and the density of.the product making it comparatively a lighterfinal product. It also confers very desirable nailing properties and in some instances fire resistance. The suitable examples are exfoliated vermiculite, expanded perlite pulverised fuel ash floaters etc.

The fibrous reinforcing material may comprise inorganic or organic fibres or a combination of both.

Preferably the fibres comprise from 1% to 25% of the total weight of the solids.

The inorganic fibres in reinforcement are low-alkali borosilicate glass fibres commercially available and popularly known as "E" glass and glass of similar as well as alkaii resistance compositions. The inorganic fibres would also include mineral wool, fibres, slag wool fibres, rock wool fibres, ceramic fibres, aluminium fibres, silica-alumina fibres, aluminium silicate fibres and metal fibres.

The organic fibres include cellulose fibres, polyamid fibres, (e.g. Nylon), Polyester fibres (e.g. Terylene) polyolefin fibres, polypropylene fibres, carbon fibres, viscose fibres, jute fibres, flax, cotton, straw, grass, sisal, hemp, bamboo etc.

The fibrous reinforcing materials will improve tensile and/or impact resistance and will impart the useful property of holding the matrix together after cracking. Certain inorganic fibres will help to improve the fibre resistance of the product.

The inorganic binder is a water-settable calcium sulphate binder, plaster of paris, Retarded Hamihydrate plaster, Anhydrous Calcium Sulphate, Anhydrate or any of the propriatary brands of plaster, or a mixture of any two or more of these. The term 'water settable binder" used herein means a binder which is caused to set by the action thereon of H20 in any of its forms, i.e. water, atmospheric moisture, steam, water holding polymers or rubber in solution or suspension.

Preferably, the binder forms between 50 to 99% by weight of the total weight of solids.

For some purposes other filler materials may also be present in the composition and when present they may be used in amounts up to 50% by weight based on the total solid content of the composition. Typical fillers include perlite, mica, pulverised fuel ash, fillite, cenospheres, lime, china clay etc.

When making a product from composition according to the invention, it is normal practice to mix the dry materials together, i.e. plaster vermiculite and fibres. The mixing may be achieved depending on the quantities by stirring with a stirrer, in a pan, paddle drum or any other type of mixer suitable for the purpose.

Water and liquid rubber or liquid polymer are mixed together in a separate container with or without the help of stirring device. Additional material may be added as accelerators or retarders to reduce or increase the setting time depending upon the circumstances. The liquid and solid contents are thoroughly mixed together. The mix may be either stiff or in the form of a slurry depending upon the relative proportions of solids and liquid contents. Since the setting of the plaster is comparatively a quick process, the mix is very quickly transferred on to the mould. The process of vibration may be used to help to fill every minute detail in the mould and to remove air bubbles at the surface. The mould must be rigid, semi-rigid or a flexible one and may be mounted on a rigid or a non-rigid base and the entire assembly may be subjected to vibration.The term mould includes any flat or curved surface on which the mix composition is applied and would therefore include parts of the human or animal body when the composition is used for medical purposes.

When the initial set has taken place, the composition can be cured under warm or hot air for the drying purposes and for strength development.

For the purpose of illustrating the invention, the following examples are given. All parts are by weight.

Example 1 A mixture of 3000 parts of British Gypsum coarse casting hemihydrate plaster was mixed with 400 parts of exfoliated superfine vermiculite and 90 parts of 25 mm long "E" glass fibres. The dry constituents were thoroughly mixed. 2000 parts of water and 600 parts of copolymer emulsion "Emultex AC 43" were thoroughly mixed. The liquid portion was then added to the solid constituents previously mixed and stirred continuously for about a minute. The resulting slurry was poured into a mould while the entire mould assembly was vibrated. The entire operation was completed in a matter of minuted. The specimen was ready for demoulding within half an hour.

Compared to an equivalent plain plaster product, the novel composition casting has: (i) a dried density reduction of 20%; (ii) a flexural tensile strength increased by 300%.

(iii) an impact strength increased by 30%.

Consequent on these strength improvements, the thickness of the casting could be reduced by at least 50%, thereby reducing the volume of the casting by approximately 50%. This then results in massive weight savings.

In addition, the novel composition can be: (i) nailed without cracking; (ii) sawn, planed, whittled without causing surface damage.

Example 2 A mixture of 300 parts of hemihydrate plaster was mixed with 30 parts of exfoliated superfine vermiculite and 6 parts of cellulose fibre. The dry constituents were thoroughly mixed. 310 parts of water and 30 parts of copolymer emulsion "Mowilith D55" were thoroughly mixed. The liquid portion was then added to the solid constituents previously mixed and stirred continuously for about 30 seconds. The resulting slurry was poured into a mould. No vibration was employed. The specimen was ready for demoulding within half an hour.

On drying, the specimen was tested, the properties are as follows: (i) dry density = 670 kg/m3 (i.e. approximately 1/3 lighter than water); (ii) flexural tensile strength = 7.375 N/mm2; (iii) impact resistance - even after dropping on the floor for several time the specimen remained intact.

(iv) can be nailed without cracking; (v) sawn, planed, whittled without causing surface damage.

Example 3 A different technique was adopted for the construction of a complicated patterned ceiling rose. Two stage pouring technique was adopted: 12 mm long Plaster Vermiculite Eglassfibres AC43 Water MIXA 1500 200 - 300 1000 MIXB 1500 200 45 300 1000 The ceiling rose was placed on the vibrating table and vibration started. As described in Example 1, the solids and liquid constituents were mixed together for each mix in separate containers. The Mix A was poured into the mould and was immediately followed by Mix B. This resulted in the first Mix A filling up all the minute details of the mould. This was achieved by the weight of the second mix and vibration which displaced the surplus quantity of Mix A. As there was very little time lag between the two pours, the final product was a strong, nailable, well formed ceiling rose with very fine details and no honeycombing.

Number of mixes with varying properties have been evaluated. These confirm the versatility of the new composition.

The invention includes a composition co-ordinating gypsum plaster, poly-vinyl acetate (or another similar bonding material) and an aerating agent, therefore producing plaster cornices, niches, statues, wall panels, etc. from this mater al, which, as far as we can see, can be fixed with no difficulties whatsoever. Also nails can be driven through this material and mitres can be cut off at angles without the material crumbing away.

The reason for this is the mix of plaster poly-vinyl acetate (or another similar bonding agent) and an aerating agent.

Claims

1. A composition for use in the manufacture of a plaster product, the composition comprising : (i) a water-settable inorganic binder which is one or more of a calcium sulphate binder, Plaster of Paris, Retarded Hemihydrate plaster, An hydrous Calcium Sulphate, Anhydrate or any of the proprietory brands of plaster; (ii) water; (iii) Polymers, and Copolymers which may be water dispersible e.g. polyvinyl acetates, styrene butadienes, acrylics, polyesters, epoxies and other resinous or rubber based materials; (iv) fibrous reinforcing materials, comprising inorganic or organic fibres or combinations of both.

2. A composition for the manufacture of a plain, patterned or decorative plaster product comprising (i) compounds arranged for the formation of calcium sulphate binder, (ii) water; (iii) compounds arranged for the formation of liquid polymer, and (iv) fibrous reinforcing material comprising inorganic and/or organic fibres.

3. A composition as claimed in Claim 1 or Claim 2, including an aerating agent in the form of a lightweight filler.

4. A composition as claimed in Claim 3, in which the lightweight filler comprises expended vermiculite, expanded perlite, sawdust, pulverised fuel ash, floaters, polystyrene beads, or any combination thereof.

5. A composition as claimed in any one of the preceding claims, in which the polymer is in liquid form.

6. A composition as claimed in any one of the preceding claims, in which the polymer is such as to impart flexibility and also increase tensile and/or impart resistance to products manufactured from the composition.

7. A composition as claimed in any one of the preceding claims, in which the polymer comprises 1% to 75% of the total weight of the composition.

8. A composition as claimed in Claim 7, in which the polymer comprises 1% to 30% of the total weight of the composition.

9. A composition as claimed in any one of the preceding claims, in which a liquid polymer is used, the solid content of the liquid polymer comprising not less than 10% of the weight of the liquid polymer.

10. A composition as claimed in Claim 9, in which the solid content of the liquid polymer comprises 40% to 60% of the weight of the liquid polymer.

11. A composition as claimed in any one of the preceding claims including a liquid weight filler comprising up to 49% of the total weight of the solids of the composition.

12. A composition as claimed in any one of the preceding claims, in which the fibres comprise from 1% to 25% of the total weight of the solids of the composition.

13. A composition as claimed in any one of the preceding claims incorporating inorganic filler in the form of low-alkali borosilicate glass fibres, mineral wool fibres, slag wool fibres, rock wool fibres, ceramic fibres, aluminium fibres, silica-alumina fibres, aluminium silicate fibres, metal fibres, or any combination thereof.

14. A composition as claimed in any one of the preceding claims, incorporating organic filler in the form of cellulose fibres, polyamide fibres, polyester fibres, polyolefin fibres, polypropylene fibres, carbon fibres, viscose fibres, jute fibres, flax, cotton, straw, grass, sisal, hemp, bamboo or any combination thereof.

15. A composition as claimed in any one of the preceding claims, in which the inorganic binder forms from 50% to 99% by weight ofthetotal weight of solids of the compositions.

16. A composition substantially as hereinbefore described, with reference to any one of Examples 1 to 3.

17. A method of manufacturing a plaster product using a composition as claimed in any one of the preceding claims, comprising mixing the dry materials together in a first container, mixing water and liquid polymer together in a separate container, and then thoroughly mixing together the dry and liquid materials.

18. A method of manufacturing a plaster product as hereinbefore described, with reference to any one of Examples 1 to 3.

19. A plaster product when manufactured using the composition as claimed in any one of Claims 1 to 16, and/or the method as claimed in Claims 17 or 18.

20. A plaster product as claimed in Claim 19, comprising a ceiling rose, cover frieze, dado rail, cornice, fireplace surround, ceiling tile, ceiling decoration, wall decoration, wall panel, door panel, board, skirting board, architrave, door casing, door head, pilaster, decorative moulding strip, medical orthopaedic plaster cast, bust, statue, chess, draughts or other games piece, or carrom board.