GB2376229A

GB2376229A - Plaster composition containing a colourant

Info

Publication number: GB2376229A
Application number: GB0113869A
Authority: GB
Inventors: Paul Simon Woolfenden
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-06-07
Filing date: 2001-06-07
Publication date: 2002-12-11
Also published as: GB0113869D0

Abstract

A plaster composition comprises a plaster containing a colourant. Typically, the plaster is white and comprises gypsum. The colourant may be a water-based paint, an acrylic paint, or an emulsion paint. A method of preparing the plaster composition is also disclosed, which comprises mixing the plaster with water and the colourant. Preferably, the plaster and the water are at least partially mixed before the addition of the colourant. The plaster and water may be mixed in a weight ratio of 2:1.

Description

Plaster Composition and method of making the same This invention relates to a plaster composition having a desired colour and a method of preparing and using the same.

The covering of surfaces, e. g. walls, using plaster is a well-known method to improve finish. Plaster material used for covering interior surfaces typically comprises gypsum. The plaster itself typically has a plain or unattractive appearance since the plaster is usually pink or grey. Therefore it is common to paint, hang wallpaper or add other surface coating for decoration and/or protection of the surface.

However, the plaster must first be allowed time to dry sufficiently before applying the paint, wallpaper or other coating. Accordingly, the overall time from applying the plaster to achieving the finished, e. g. painted, surface can be considerable. Moreover, clearly this practice requires at least two distinct operations: plastering and a subsequent decorating step, having associated labour. Furthermore, if a coating such as paint has been applied over plaster a sizing step or abrasion step required to give sufficient adhesion before any further plaster can be applied on top. A further limitation of the common practice is that physical damage of the paint or other surface coating may lead to the colour of the plaster showing through. In addition, marking of the paint or other surface coating, e. g. by pens, crayons etc. , can be difficult to remove.

An object of the present invention is to overcome or reduce the aforementioned disadvantages.

According to a first aspect of the present invention there is provided a plaster composition comprising a plaster having mixed therein a colourant.

The invention has a number of advantages over previous methods, since the plaster is itself coloured by the colourant therein. The colour may be any chosen by the user. A

surface prepared using the plaster composition requires no subsequent painting or other surface coating. Therefore, no time is required for a subsequent operation and the total cost of labour is greatly reduced. In addition, if the plastered surface is indented, scratched or otherwise physically damaged, the damage is barely visible because the underlying plaster revealed by the damage is the same colour as the surrounding surface plaster. It is another advantage of the invention that the plaster surface can be effectively renewed by selectively abrading or polishing to reveal fresh underlying plaster. As a consequence of the last feature, the removal of graffiti or other marking of the surface can be readily achieved by abrading the affected plaster thereby removing the surface marking, in doing so creating a new, unmarked surface.

Furthermore, new coloured surface effects may be obtained, that were previously unobtainable, by actively using abrasion to create a novel coloured textured finish, for example by sand blasting. Moreover, because the plaster is coloured, a pleasing appearance may be attained even if the plaster surface is not particularly smooth or even. Therefore a person with a low degree of skill in plastering may adequately cover and decorate a wall or similar surface with ease. As mentioned, a disadvantage of the prior art arises from the fact that the painting of conventional plaster removes surface porosity and a sizing or abrasion step or application of a Poly Vinyl Alcohol/Acetate (PVA) building adhesive is typically required prior to further plastering. However, because the surface of the plaster according to the invention does not require painting, should the plastered surface require further coating, for example, in a redecoration process or repair process, then the surface can be coated for example by subsequent plastering, pasting or even painting, with less need for, for example, a sizing step or a PVA coating. However, an amount of PVA building adhesive, for example, may still be applied to the plaster surface of the invention to aid adhesion of subsequent plaster etc. Further advantages will become apparent from the following description.

The plaster of the invention is preferably a white coloured plaster. A near white plaster is also suitable, although this is not as preferred as pure white. For convenience, the term substantially white is used herein to mean a white or near

white plaster. Suitable plasters may have a gypsum purity of at least 95%. The plaster may comprise a pre-mixed retarded gypsum plaster. The gypsum may comprise the hemihydrate. A suitable plaster for the invention includes a white pre-mixed retarded calcium sulphate hemihydrate plaster having a gypsum purity of at least 95%.

Pink or grey gypsum plasters have been found to be less suitable for use in the invention. This is because for practical use it is necessary to re-produce a colour without recourse to sophisticated matching and adjustment techniques to take account of the base plaster colour. The use of a substantially white plaster is such that the colour of the colourant is substantially unaffected by mixing in the plaster.

Accordingly, the colour of the coloured plaster remains faithful to the original colour of the colourant.

Preferably, the plaster of the invention comprises gypsum (hereinafter a gypsum plaster) and more preferably a substantially white gypsum plaster. Such gypsum plasters are suitable for plastering the interior surfaces of a building.

The plaster may have a setting time when contacted with water in a weight ratio of plaster: water = 2: 1 of from ten minutes to twenty minutes. A suitable white gypsum based plaster material is available from KNAUF (Sittingboume, Kent), sold as the grade :"Universal Board Finish" (Article Number 729.02. 000) complying with British Standard 1230 (1985) part 1. Other suitable white gypsum plasters sold by KNAUF, are the products"Multicover", (Art. No. 788 02 000) ;"Ultimate Backing Plaster", (Art. No. 756 02 050) and"Gold Band", (Art No. 159 02 000). The foregoing examples of suitable white gypsum plasters have a gypsum purity of at least 95%. Moreover, such examples are pre-mixed retarded calcium sulphate hemihydrate plasters, needing only addition of water.

The colourant may be any substance suitable for imparting colour to the plaster. For example, the colourant may comprise a pigment, paint, dye or ink. However, paint has been found to be particularly useful. More preferably, the paint should be water

based. Such water based paints are readily available as shelf items and mix well with the plaster without significant separation. Preferred examples are acrylic or emulsion paints. Use of such paints moreover does not produce significant smell.

Advantageously, the water based paint does not weaken the plaster. The paint may improve the heat resistance of the plaster. i. e. reduce cracking of the plaster under heat.

Water proofing of the plaster composition may be achieved by including a latex bonding compound in the composition. Alternatively, a waterproof coating may be applied to the finished and applied plaster composition. The waterproof coating may comprise a clear impregnation of an amino functionalised siloxane polymer in water such as that sold as"Modified Nu-Sil AG"by Nucoat Protective coatings Ltd (Wolverhampton, England).

According to a second aspect of the invention, there is provided a method of preparing the plaster composition of the first aspect, comprising mixing a plaster with water and a colourant. Preferably, the plaster and water are at least partially mixed before addition of the colourant. Further preferably, the colourant is added after mixing the plaster and water for approximately two minutes.

Preferably the plaster and water are mixed in an approximate weight ratio plaster : water = 2 : 1. Further preferably, the plaster is soaked in the water prior to the mixing.

Additionally preferably, the plaster and water are mixed under low shear conditions, prior to addition of the colourant. Preferably, the low shear mixing of plaster and water is carried out using a paddle or stick. This is in contrast to conventional mixing of gypsum plaster which uses high shear conditions such as are provided by an electric whisk.

Preferably the colourant is in a liquid form. The weight ratio of plaster: colourant can be varied and depends upon the type of colourant, the strength of colour needed

etc. The colourant is preferably also mixed with the plaster using a paddle or stick, i. e. under low shear conditions.

The degree of mixing in of the colourant depends upon the desired colouration effect in the finished plaster. The colourant may be completely mixed in the plaster to give a homogenous colour to the plaster. Alternatively a series of decorative effects may also be readily produced from partial mixing of the colourant. This has the advantage that uneven plaster work may be further disguised by the uneven distribution of the colourant. Similarly, a plurality of colourants may be applied such that a surface may be coloured by several colours all in one process further enhancing the time saved as compared to a painting operation using several colours.

In a third aspect, the invention provides the use of the plaster composition for finishing a surface.

A particularly useful feature of the invention is the creation of a coloured surface which is porous. Conventional plaster coated surfaces when painted or when polished are liable to condensation as the surface cannot readily loose moisture or'breathe'as it is termed in the trade. Gloss paints particularly create such a problem by being water impervious. The present invention therefore gives a method of creating a plaster coating which is both coloured, whilst not requiring painting, and 'breathable'. It is therefore ideally suited to damp environments, such as kitchens and bathrooms. For such environments the invention may also be combined with a proprietary fungicide.

The invention is now illustrated by the following example; 10 kg of a white gypsum based plaster: KNAUF"Universal Board Finish", (article number 729.02. 000) supplied by Knauf GmbH, is added to a clean 25 litre container and then 5 litres of cold tap water are poured in. This is left to soak without substantial agitation for 1 to 2 minutes. Then, the plaster and the water are gently mixed using a stick stirrer. After about 2 minutes of mixing, 1 litre of water based

paint, Benetton (TM)"lime green", is then added. At this stage it can be chosen how much to mix in the paint depending on the desired end product. The mix may at this stage be optionally mixed thoroughly to remove inhomogeneity in colouration or may be left partially mixed to retain inhomogeneity as a decorative effect. For homogeneous mixing, the continued low shear stirring may be performed over a period of one to five minutes. This mixed coloured composition is then applied to a plaster board by a conventional plastering technique and left to cure for twenty four hours. This results in an evenly pastel coloured hard surface not requiring further decoration. As an optional further step, the above finished surface was waterproofed by the application of a water proof sealant,'Modified NU-SILTM A. G. supplied by NuCoat Protective Coatings Limited, UK. After 24 hours the surface was waterproof and more resistant to marking or staining yet the coloration remained.

Claims

Claims 1. A plaster composition comprising a plaster having mixed therein a colourant.
2. A plaster composition according to claim 1 wherein the plaster is white or near white.
3. A plaster composition according to either claim 1 or 2 wherein the plaster comprises gypsum.
4. A plaster composition according to any one of claims 1 to 3 wherein the colourant comprises a paint.
5. A plaster composition according to claim 4 wherein the paint comprises a water based paint.
6. A plaster composition according to claim 4 or 5 wherein the paint comprises an acrylic or emulsion paint.
7. A plaster composition substantially as herein before described with reference to the illustrative example.
8. A method of preparing the plaster composition according to any one of claims 1 to 7, comprising mixing a plaster with water and a colourant.
9. A method of preparing the plaster composition according to claim 8 comprising at least partially mixing the plaster and water before adding the colourant.
10. A method of preparing the plaster composition according to claim 9 comprising adding the colourant after mixing the plaster and water for approximately two minutes.

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11. A method of preparing the plaster composition according to any one of claims 8 to 10 wherein the plaster and water are mixed in an approximate weight ratio of plaster: water 2 : 1.
12. A method of preparing the plaster composition according to any one of claims 8 to 11 wherein the plaster and water are mixed under low shear conditions.
13. A method of preparing the plaster composition according to any one of claims 8 to 12 wherein the plaster and water are mixed with a paddle or stick.
14. A method of preparing a plaster composition substantially as herein before described with reference to the illustrative method.
15. The use of the plaster composition according to any one of claims 1 to 7 for finishing a surface.