GB2069522A - Paint strippers - Google Patents

Abstract

The present invention relates to a spreadable aqueous paint stripper composition comprising an alkali in an amount capable of stripping paint. The composition includes one or more skin forming promoter components whereby when the composition is applied as a layer over a painted surface to be stripped it forms over the surface a peelable skin, the skin having a tear strength sufficient for it to be separated and removed from the underlying surface and an adhesive strength sufficient to separate and remove from the underlying surface paint softened by contact with the composition. In one embodiment the skin forming component comprises a fibrous material, preferably together with one or more gelling agents and/or a filler. In a second embodiment the skin forming components comprise a filler, a xanthan gum and a synthetic hectorite clay. The composition forms a peelable skin greatly facilitating the stripping operation.

Description

SPECIFICATION Paint strippers This invention relates to paint strippers, and in particular to alkali-based stripping compositions.

When redecorating it is frequently desirable to remove old layers of paint, either to provide a good basis for new paint or to expose the underlying surface. Traditionally, a blow-torch has been employed to soften the old paint which is removed with a scraper. However, this requires considerable skill, and even experienced decorators can scorch the underlying surface. This may not be a serious drawback when the surface is to be repainted, but where, for example, a cleaned wooden surface is to be left unpainted scorch marks are unsightly.

The amateur decorator therefore generally avoids using a blow-torch, and instead relies on chemical paint strippers. In general, such paint strippers are applied to the painted surface, left to allow the paint to become soft and then paint and stripper are removed together with a scraper. Paint strippers fall into two broad categories: organic solvent-based strippers and aqueous, alkaline strippers.

Organic solvents are used as the basis for the first category of conventional strippers, often in conjunction with an alkali. These are very effective but extremely unpleasant to use because of the presence of the solvent, and the "thin" nature of the composition which leads to drips and runs.

In place of the organic vehicle water has been used to form aqueous compositions which usually contain an alkali as the active paint-stripping ingredient. Again the "thin" nature of such compositions makes them inconvenient to use, and also the tendency of the composition to evaporate and to run off vertical surfaces means that the active ingredient is not in contact with the paint long enough to result in efficient stripping.

A recent improvement is aqueous strippers has been obtained by including a gellant and a filler such as chalk in the composition to give a pasty consistency. This makes application of the stripper to a painted surface much easier and removes the problem of dripping, while removal of the stripper and softened paint from flat surfaces is greatly facilitated since is can be virtually lifted off the surface using a paint scraper. The combined stripper/paint layer has no lateral cohesion, however, so that it is necessary to remove it by passing the scraper over the entire area between the layer and the underlying surface. On flat areas this causes no difficultly but over complex curvatures, such an on chair legs or cornices, the removal is not readily accomplished with a scraper.

It has now been found that remarkably good paint stripping may be achieved particularly on surfaces bearing oil-based paint, with a stripper which forms a peelable skin over the painted surface.

The alkali is held in contact with the paint to be stripped which is thus efficiently softened, and the subsequent removal of the stripper/paint layer is greatly facilitated, particularly on complex shapes.

Accordingly, in one aspect the present invention provides a spreadable aqueous paint stripper composition, which composition comprises an alkali in an amount such that the composition is capable of stripping paint, together with one or more skin forming promoter components whereby when the composition is applied as a layer over a painted surface to be stripped it forms over the surface a peelabie skin, the skin having a tear strength sufficient for it to be separated and removed from the underlying surface and an adhesive strength sufficient to separate and remove from the underlying surface paint softened by contact with the composition.

The composition of the invention is applied as a layer over a painted surface to be stripped, and forms a peelable skin thereover. The peelable skin has a tear strength sufficient for it to be separated from the underlying surface as an integral gel. Thus, the layer of composition develops a lateral strength which permits its removal as an intact skin. However, the lateral strength need not be high for the advantages to be achieved, and the skin need not, for example, possess lateral elastic properties.

The means for providing the peelable property in the skin forming using the compositions of the invention may take a number of forms. In a first embodiment the composition may comprise fibrous material as a skin forming promoter component which bonds together the aqueous alkaline composition to form a peelable skin. Such compositions generally contain a gelling agent as a skin forming promoter component in addition to the fibre. In a modification of this embodiment the composition may contain a filler as an addition skin forming promoter component to thicken the composition and increase the absortive properties of the peelable skin.

In an alternative embodiment no fibrous material is employed, but the peelable property is achieved by thickening the composition with filler and employing a particular combination of gelling agents.

Thus, in its broadest aspect the first embodiment of the invention mentioned above is a spreadable aqueous composition comprising an alkali and an appropriate amount of fibrous material, the composition being sufficiently alkaline to strip paint.

The alkali is most conveniently an alkali metal hydroxide since these give a highly alkaline composition and are readily available and are cheap; sodium and potassium hydroxide are preferred.

However, it is possible to use other alkalis having a pH in aqueous solution greater than 10, such as alkaline silicates, for example, sodium metasilicate, and phosphates, for example, trisodium phosphates.

Other highly alkaline materials, preferably with a pH greater than 12 and most preferably with a pH greater than 1 3, are well known in the art and could be used in the conpositions of the invention.

Sodium hydroxide is generally most preferred for use as the alkali, as other compounds are more expensive and milder or slower acting. If desired sodium hydroxide may be provided by using a mixture of sodium carbonate and calcium hydroxide.

In some applications, such as where there may be a danger of staining the surface under the paint, it may be desirable to select a milder alkali, and in that case trisodium phosphate might be used.

The concentration of alkali in the composition will be selected according to known criteria, and this selection is believed to be within the competence of one skilled in the art. When sodium hydroxide is used as the alkali, it would be possible to employ concentrations of 25% by weight or higher.

However, it is preferred to use no more than 12% sodium hydroxide since this avoids restrictions in use resulting from regulations for handling poisons in the U.K. The lower concentration limit is determined by the paint stripping job for which the composition is intended, and could be as low as 1% or even lower. However, the usual concentration range for sodium hydroxide is from 3% to 12% and most preferably from 3% to 7%. Within those preferred ranges the particular concentration is selected having regard to the speed of stripping that is required, set against the effect on the cost of the stripper.

When other alkalis are used the preferred concentrations would be judged on a similar basis.

Potassium hydroxide may be used at concentrations of up to 17% without requiring special treatment under U.K. poisons regulations, so this alkali might be preferred when a higher concentration was needed. A likely concentration range for the alkaline salts mentioned hereinbefore is from 30% to 40%.

The compositions preferably contain a gelling agent as an additional skin forming promoter component, and this may be a natural or synthetic, water-soluble polymer, Such gelling agents are well known to those skilled in the art. Examples of appropriate agents are polyacrylic acid and its esters, starch, natural gums such as gum tragacanth or British gum, cellulose ethers, hydroxyethyl cellulose, xanthan gums and synthetic clays such as montmorillite clays. Preferred gelling agents are the xanthan gums and synthetic clays. An example of a commercially available xanthan gum is Kelzan, a high molecular weight natural polysaccharide produced in a pure cuture fermentation process by the microorganism Xanthomonas campestris, and available from Kelco, a division of Merck and Co. Inc.A preferred synthetic clay is Laponite, which is a synthetic hectorite-a magnesium silicate containing lithium, and fluorine or hydroxide groups in a layered structure. This clay is available from Laport Industries Limited.

The amount of gelling agent used is selected on the basis of the thickness required for the composition having regard to the properties of the particular gelling agent used. It is not possible to indicate preferred ranges for gelling agent in general, since different agents are used at different concentrations to achieve the same degree of gelling. However, it is believed to be within the competence of one skilled in the art to select an appropriate gelling agent concentration. By way of illustration only, it may be said that it is unlikely that the gelling agent will be used in concentrations in excess of 10% by weight, while a convenient lower limit is 0.1%. Examples are given hereinafter which further illustrate suitable concentrations of gelling agent in particular compositions.

The fibrous material in the first embodiment of the invention functions to hold together the gelled layer of compositon on the painted surface, and so make the layer peelable. A wide variety of organic and inorganic, natural and synthetic fibres may be used to contribute peelability to the compostion, provided that the fibre is not degraded by the other components of the composition at the concentrations employed. The fibres may be, for example, ground paper, flaked paper, paper punchings, wool, textile fibres asbestos, wood pulp, or plastics material fibre such as a viscous fibre or ground synthetic leather. These forms of fibre are relatively cheap since they are derived from waste materials, and ground paper in particular provides a cheap source of fibre and for that reason is preferred.

The fibre used is preferably in the form of relatively short individual fibres, by which it is meant that the fibres do not exceed 10 mm in length. A preferred form of random ground paper fibre has fibres with iengths of up to 2 mm.

The fibre content of the compositon is chosen to give the desired degree of peelability in conjuction with the selected gelling agent. Typically the fibre will constitute no more than 25% by weight of the compostion, and in general compositions will contain no more than 1 5% fibre and preferaqbly no more than 12% fibre. Too much fibre may lead to the composition being too thick for it to be applied conveniently to the surface being stripped. A preferred lower limit is about 5% fibre, while excellent peelability is achieved with fibre contents of not less than 8%.

The fibre-containing compositions of the invention may also contain a filler-that is to say, a solid particulate component substantially inert to the other components of the composition and to paint, again as an additional skin forming promoter component. This filler acts to bulk out the composition and increase its thickness. In addition, when the composition is in use the filler absorbs the liquified paint which has been attacked by the alkali, and helps to prevent runs. Suitable fillers which may be used include powdered chalk, clay, fly ash, vermiculite and wood flour. Of these powdered chalk is most preferred for use in the invention.

The filler should not be employed in a concentration at which the composition becomes too thick to be spreadable, and clearly the amount of filler which may be employed to give a spreadable composition is affected by the amount of fibre present. In general, when filler is present the amount of fibre may be reduced. It has been found desirable for up to 64% filler to be used in conjunction with up to 20% fibre, and effective compostions may be obtained with filler and fibre even when the amount of fibre is below 5%, which is the preferred lower limit for fibre content in the absence of filler. It has been found that the ratio of filler to fibre is most conveniently in the range of from 6:1 to 1 :1, and most preferably in the region of 4:1.

It has also been found that peelable compositions may be obtained without the use of fibre, by using filler in conjunction with a specific combination of gelling agents. Thus, in the alternative embodiment this invention provides a spreadable composition comprising an alkali, filler, a xanthan gum and a synthetic hectorite clay, the composition being sufficiently alkaline to be capable of stripping paint.

The alkali used in this embodiment is selected according to the criteria set out hereinbefore and employed at the concentrations previousiy suggested.

The filler may be selected from those materials identified hereinbefore, but is generally used at somewhat higher concentrations. The filler will generally be present in an amount of at least 25% by weight, and preferably of up to 75% by weight Most preferably the amount of filler lies in the range of from 50% to 70% in the fibre-free compositions. The actual amount of filler used is determined by the rheological properties of the compositions, which are in turn set by the nature and concentrations of the gelling agent. In qualitative terms, the amount of filler should not be so low as to result in a slurry which would tend to run off a surface being stripped, neither should so much filler be present that the composition cannot readily be spread onto a surface.

In a preferred embodiment the composition is thixotropic, but naturally even when it exhibits this property it should become sufficiently mobile on being worked to permit spreading.

It has been found that a particular combination of gelling agents is required to obtain peelability in a composition containing filler and no fibre. The xanthan gum is preferably Kelzan gum, and the clay is preferably Laponite. These gelling agents are preferably used at concentrations of from 0.2% to 4% Kelzan and from 0% to 2.0% Laponite, the ratio of Kelzan to Laponite being in the range of from 5:1 to 1:1.

Both types of compositions of the invention, and thus whether or not containing fibre, may also include other standard ingredients for paint stripping compositions such as wetting agents, dyes, preservatives and water-miscible organic solvents. All such additives must of course be compatible with the other ingredients, and in particular be compatible with the alkalinity of the compositions, as well as being water-miscible. The selection of these conventional ingredients and suitable concentrations for them is believed to be within the competence of one skilled in the art.

By incorporating a bleach into any of the compositions of the invention it would be possible to provide a paint stripper which would bleach the underlying surface. Conventional bleaches such as sodium chlorate or hydrogen peroxide may be used, typically at a concentration of from 0 to 1 0% by weight of the composition.

In use the compositions of the invention are applied to a painted surface typically as a layer of up to 3-4 mm thick. It is convenient to apply the composition to the surface with a trowel or similar spreader. the composition is then left until the paint bas been softened; typically this will be a period of from 1 to 6 hours, although longer periods of contact may be desirable when many coates of paint are to be removed. If the layer of composition dries out during this time, it can be sprayed with water to dampen it and ensure maximum contact of the alkali with the paint.

The layer of composition is then removed as a peelable skin using a scraper or similar tool although actual scraping of the underlying surface should not be necessary. The skin is lifted away from the surface together with the softened paint, and complex shapes can be readily stripped without having to scrape paint from every crevice.

In a second aspect the invention thus includes a method of stripping a paint layer from an underlying surface, which method comprises applying to the paint layer an effective amount of a composition as described herein, allowing the composition to form a peelable skin in conjunction with paint softened by the action of the composition, lifting the formed skin and peeling it away from the underlying surface to strip the paint therefrom.

The compositions of the invention have been described above in their ready-to-use form. It is to be understood, however, that the compositions of the invention may be produced for distribution and sale in dry powder form. Accordingly, the present invention in another aspect provides a composition in dry powder form which when mixed with water can form a spreadable aqueous paint stripper composition as described herein.

The dry powder composition may the same as the spreadable aqueous composition, except for the inclusion of water. However, since at least some of the alkali materials described above may not be conveniently handled in dry form, it is preferred to formulate the dry composition with a mixture of calcium hydroxide (lime) and an alkali metal salt, the anion of which forms an insoluble salt with calcium. The ingredients of such a mixture when mixed with water provide an alkali metal hydroxide e.g.

sodium hydroxide, but when in dry form are more easily handled than the corresponding alkali metal hydroxide.

Preferably, the alkali metal salt and the calcium hydroxide are employed in substantially stoichiometric amounts, the percentage of each in the dry composition being such as to provide a corresponding percentage of alkali metal hydroxide in accordance with the above description, preferably 3 to 12% by weight of hydroxide.

Since the dry powder composition is especially useful as a do-it-yourself product, it may if necessary be formuiated with an increased amount of filler (where present) to facilitate mixing with water. Thus, for example, where a filler and fibre together are employed the ratio of filler to fibre may be up to about 7:1.

Preferably the dry powder composition includes a mixture of lime and sodium carbonate to provide sodium hydroxide when mixed with water.

The following Examples are now given, though only by way of illustration, to show aspects of the invention in more detail.

Example 1: Paint stripper containing fibre and filler A composition was prepared from the following ingredients: Grams Kelzan 26.2 Sodium hydroxide solution (48% w/w) 104.6 Ground paper 104.6 Chalk 104.6 Water 660.0 1000.0 grams Example 2: Paint stripper containing fibre A composition was prepared from the following ingredients: Grams Kelzan 26.2 Laponite S 10.7 Sodium hydroxide solution (46% w/w) 104.6 Ground paper 104.6 Water 753.9 1000.0 grams Example 3: Paint stripper containing filler A composition was prepared from the following ingredients: Grams Kelzan 10.5 Laponite S 4.5 Sodium hydroxide solution (46% w/w) 83.3 Chalk 640.0 Water 261.9 1000.0 grams Example 4:Paint stripper containing filler and fibre A thixotropic composition was prepared from the following ingredients: kg Kelzan 1.00 Laponite S 0.50 Sodium hydroxide solution (46% w/w) 10.45 Chalk 34.83 ,16'ground paper (1.6 mm) 7.46 Water 45.77 100.01 kg Example 5: Paint stripper containing filler and fibre A composition was prepared from the following ingredients: kg Kelzan 0.871 Laponite S 0.435 Sodium hydroxide solution (46% w/w) 10.45 Chalk 37.31 81' flaked paper (3.2 mm) 8.71 Water 42.226 100.00 kg Example 6: Paint stripper containing filler and fibre A composition was prepared from the following ingredients: % wlw Kelzan 2.6 Sodium hydroxide 5.0 T ground paper (3.2 mm) 10.5 300 mesh wood flour 10.5 Water 71.4 Example 7:Paint stripper containing filler and fibre A composition was prepared from the following ingredients: % w/w Kelzan 2.6 Sodium hydroxide 5.0 500 mesh vermiculite 10.5 8 ground paper (3.2 mm) 10.5 Water 71.4 Example 8: Paint stripper containing filler and fibre A composition was prepared from the following ingredients: %w/w Kelzan 2.0 Laponite 0.8 Sodium hydroxide 5.0 Chalk 21.0 500 mesh vermiculite 10.5 r6 ground paper (1.6 mm) 5.0 Water 55.7 Example 9: Paint stripper containing filler and fibre A composition was prepared from the following ingredients: % w/w Kelzan 1.0 Laponite 0.5 Potassium hydroxide 5.0 Chalk 35.0 $" flaked paper (3.2 mm) 7.5 Water 51.0 Example 10:Paint stripper containing filler and fibre A composition was prepared from the following ingredients: % w/w Kelzan 2.6 Sodium hydroxide ' 5.0 Chalk 10.5 Viscose fibres 10.5 Water 71.4 Example 11: Paint stripper containing fibre and filler A composition was prepared from the following ingredients: % w/w Water 58.2 Chalk 15.7 41' Flaked paper (6.35 mm) 15.7 Sodium hydroxide (48% w/w) 10.4 100.0 The pH of the compositions of Examples 1 to 11 fall within the range of from 13 to 14.

Example 12: Paint stripper containing fibre and filler A composition was prepared from the following ingredients: /0 w/w Kelzan 1.0 Laponite S 0.5 Trisodium phosphate 10.0 Chalk 34.8 all ground paper (1.6 mm) 7.5 Water 46.2 The pH of this composition was 11.8 Example 13:Paint stripper containing fibre and filler A composition was prepared from the following ingredients: % wlw Kelzan 1.0 Laponite S 0.5 Sodium metasilicate 10.0 Chalk 34.8 8xZ flaked paper (3.2 mm) 7.5 Water 46.2 The pH of this composition was 12.7 % {w/wJ Gelling agent (viscalex HV30--an acrylic copolymer emulsion available from Allied Colloids Limited) 3.0 Sodium hydroxide 4.0 Chalk 66.5 Anti-foaming agent 0.2 Water 26.2 The following Test Results are now presented, again only by way of illustration, to show the results obtained when stripping paint with a prior art composition and with the composition of the invention.

Test Results Method Paint stripping compositions were tested for their efficacy in removing four layers of oil-based paint from a wood surface. The painted-surface was divided into tests areas approximately 6 inches (15 cm) x 4 inches (10 cm) using pieces of self-adhesive plastics tape. A paint stripper composition under test was applied to a test area using a trowel or spatula to a thickness of approximately 8 inch (3 mm) judged by eye. The composition was left in contact with the test area for a period of time and then removed using a spatula. The nature of the composition at the time of removal, the ease of removal and the amount of paint stripped was assessed. The results are set out hereinafter.

Results To provide a comparison, a prior art paint stripper was tested. The composition of this prior art stripper was: In separate tests this prior art composition was left in contact with test areas for 3 hour and 2 hours.

The results are given in Table 1 below.

TABLE 1

Nature at Paint Composition Gontact time (hours) removal stripped Prior art 2/3 Paste 80% Prior art 2 Paste 100% In each case the paint stripper composition was removed as a paste; it showed no cohesion and was not peelable. As a result it was necessary to scrape the paste off the stripped surface, which was a messy and time-consuming operation. After 32 hour 80% removal was achieved-that is to say, all four layers of paint were removed over 80% of the test area. After 2 hours 1 00% removal was achieved, and all four layers of paint were stripped from the test area.

The results obtained in testing compositions of the invention are set out in Table 2 below, in which the compositions are identified by reference to the Example in which the formulation details are given.

TABLE 2

Contact time Paint Composition (hours) Nature at removal stripped 1 1 Peelable ski n 100% 2 1 ,, 100% 3 1 " 100% 4 1 " 100% 4 2/3 ,, 100% 5 1 " 100% 6 1 ,, 100% 7 1 " 100% 8 1 " 100% 9 1 " 100% 10 - 1 " 100% 11 10 Dry peelable skin 100% 12 5 Peelable skin * 13 5 " " * One layer completely removed, a second layer removable with scraping ** Approximately 90% removal with scraping.

In each case the composition tested formed a peelable skin which could be lifted away from the test area in one piece together with the paint softened by the alkali. With the compositions containing sodium hydroxide or potassium hydroxide 100% removal was obtained without scraping; it was simply necessary to wash down the stripped area after removing the skin to leave a clean stripped wood surface. The compositions containing trisodium phosphate and sodium metasilicate are intended to be milder so that they may be used on delicate workpieces or where selective removal of only top layers of paint is required. Thus, in the test complete removal of all four layers of paint was not achieved with these alkalis, but the compositions displayed the advantage of the invention in that they formed a peelable skin facilitating the stripping operation.

Example 14: Paint stripper containing fibre and filler in dry powder form.

A dry powder composition was prepared from the following ingredients: Parts by weight Sodium carbonate 5.0 Calcium hydroxide 3.5 Chalk 34.0 Granulated paper " (3.2 mm) 5.0 Kelzan 0.75 Laponite S 0.38 The above composition was suitable for transport, storage and sale in dry powder form and when mixed with water to 100 parts w/w formed a spreadable aqueous paint stripper composition which in use formed a peelable skin and afforded 100% paint removal without scraping as did those compositions containing sodium hydroxide.

Example 15: Paint strippers containing fiber and filler in dry powder form.

The compositions described in Examples 12 and 13 were formulated without water in dry powder form. When required for use the compositions were mixed with water to 100% w/w and performed in the manner described above.

Claims (43)

CLAIMS:

1. A spreadable aqueous paint stripper composition, which composition comprises an alkali in an amount such that the composition is capable of stripping paint, together with one or more skin forming promoter components whereby when the compostion is applied as a layer over a painted surface to be stripped it forms over the surface a peelable skin, the skin having a tear strength sufficient for it to be separated and removed from the underlying surface and an adhesive strength sufficient to separate and remove from the underlying surface paint softened by contact with the composition.

2. A composition as claimed in claim 1, which has a pH of at least 10.

3. A composition as claimed in claim 2, which has a pH of at least 12.

4. A composition as claimed in claim 3, which has a pH of at least 13.

5. A composition as claimed in any one of the preceding claims, in which the alkali is an alkali metal hydroxide.

6. A composition as claimed in claim 5, in which the alkali is sodium or potassium hydroxide.

7. A composition as claimed in claim 6, which contains from 3% to 12% by weight sodium hydroxide.

8. A composition as claimed in claim 7, which contains from 3% to 7% by weight sodium hydroxide.

9. A composition as claimed in any one of the preceding claims, which includes a fibrous material as a skin forming promoter component.

10. A composition as claimed in any one of the preceding claims, which includes a gelling agent as an additonal skin forming promoter component.

11. A composition as claimed in claim 10, in which the gelling agent is polyacrylic acid or an ester thereof, starch, a natural gum, a cellulose ether, hydroxyethyl celiulose, a xanthan gum or a synthetic clay.

12. A composition as claimed in claim 11, in which the gelling agent is a natural polysaccharide.

1 3. A composition as claimed in claim 12, in which the natural polysaccharide is produced in a pure culture fermentation process by the microorganism Xanthomonis campestris.

14. A composition as claimed in claim 11. in which the gelling agent is a synthetic hectorite clay.

15. A composition as claimed in any one of claims 10 to 14, which contains from 0.1% to 10% by weight of gelling agent.

1 6. A composition as claimed in any one of claims 9 to 15, in which the fibrous material comprises ground paper, flaked paper, paper punchings, wool, textile fibres, asbestos, wood pulp or a plastics material fibre.

1 7. A composition as claimed in any one of claims 9 to 16, in which the fibres do not exceed 10 mm in length.

18. A composition as claimed in claim 1 7, which contains random ground paper fibre having fibres with lengths of up to 2 mm.

19. A composition as claimed in any one. of claims 9 to 18, which contains up to 25% by weight of fibre.

20. A composition as claimed in claim 1 9, which contains from 5% to 1 5% by weight of fibre.

21. A composition as claimed in claim 20, which contains from 8% to 12% by weight of fibre.

22. A composition as claimed in any one of the preceding claims, which also includes a substantially inert particulate filler as an additional skin forming promoter component.

23. A composition as claimed in claim 22, in which the filler is powdered chalk, clay, fly ash, vermiculite or wood flour.

24. A composition as claimed in claim 22 or claim 23, which contains up to 64% by weight filler in conjunction with up to 20% by weight fibre.

25. A composition as claimed in claim 24, in which the weight ratio of filler to fibre is in the range of from 6:1 to 1:1.

26. A composition as claimed in claim 25, in which the weight ratio of filler to fibre is substantially 4:1.

27. A composition as claimed in any one of claims 1 to 8 or any one of claims 10 to 1 5, 22 or 23 when dependent on each other or any one of claims 1 to 8, which includes a filler, a xanthan gum and a synthetic hectorite clay as said skin forming promoter components.

28. A composition as claimed in claim 27, which contains from 25% to 75% by weight of filler.

29. A composition as claimed in claim 28, which contains from 50% to 70% by weight of filler.

30. A composition as claimed in any one of claims 27 to 29 which is thixotropic.

31. A composition as claimed in any one of claims 27 to 30, which contains from 0.2% to 4% of xanthan gum and up to 2% of synthetic hectorite clay.

32. A composition as claimed in claim 31, in which the weight ratio of xanthan gum to synthetic hectorite clay is from 5:1 to 1:1.

33. A composition including means capable of binding a layer of the composition to form a peelable skin, and being sufficiently alkaline to be capable of stripping paint, substantially as hereinbefore described.

34. A composition including means capable of binding a layer of the composition to form a peelable skin, and being sufficiently alkaline to be capable of stripping paint, substantially as hereinbefore described with reference to any one of Examples 1 to 1 3.

35. A composition in dry powder form which when mixed with water can form a spreadable aqueous paint stripper composition as claimed in any one of claims 1 to 33.

36. A composition in dry powder form which can be mixed with water to form a spreadable aqueous paint stripper, which composition comprises calcium hydroxide and an alkali metal salt, the anion of the alkali metal salt being one which forms a water-insolible salt with calcium, to provide alkali in an amount such that the aqueous stripper is capable of stripping paint, together with one or more skin forming promoter components whereby when the aqueous stripper is applied as a layer over a painted surface to be stripped it forms over the surface a peelable skin, the skin having a tear strength sufficient for it to be separated and removed from the underlying surface and an adhesive strength sufficient to separate and remove from the underlying surface paint softened by contact with the composition.

37. A composition according to claim 36, wherein the alkali metal salt is sodium carbonate.

38. A composition according to claim 36 or claim 37, wherein the calcium hydroxide and the alkali metal salt together provide from 3% to 12% by weight alkali metal hydroxide in the aqueous stripper.

39. A composition according to any one of claims 36 to 38, wherein the ingredients and/or their percentages and/or their proportions are as defined in any one of claims 9 to 32.

40 A composition according to claim 35 or claim 36 substantially as hereinbefore described with reference to Example 14 or Example 1 5.

41. A spreadable aqueous paint stripper comprising a composition according to any one of claims 36 to 40 mixed with water.

42. A method of stripping a paint layer from an underlying surface, which method comprises applying to the paint layer an effective amount of a composition as claimed in any one of claims 1 to 34 or claim 41, allowing the composition to form a peelable skin in conjunction with paint softened by the action of the composition, lifting the formed skin and peeling it away from the underlying surface to strip the paint therefrom.

43. A method as claimed in claim 42 and substantially as hereinbefore described.