WO2007063178A1

WO2007063178A1 - Coating mixture and method for its preparation

Info

Publication number: WO2007063178A1
Application number: PCT/FI2006/050516
Authority: WO
Inventors: Esa Silfverhuth
Original assignee: Hirvi, Antti; Railonkoski, Make
Priority date: 2005-12-02
Filing date: 2006-11-24
Publication date: 2007-06-07
Also published as: FI20051243L; FI20051243A0

Abstract

The present invention relates to a coating mixture, which comprises fine fibre material mixed into water and a water-soluble or miscible binding agent together with a mineral filling agent, to be used for coating using a method where in a first phase the binding agent is added to the water under vigorous mixing, in a second phase an optional foaming agent is added, in a third phase the fibre is added under vigorous mixing to form an airy, homogenous pulp and in a fourth phase the mineral filling agent is added.

Description

Coating mixture and method for its preparation

The present invention relates to a coating mixture according to the preamble of claim 1.

Such a mixture usually comprises a fine fibre material that is mixed with water and at least binding agent, which is water-soluble or miscible.

The invention also relates to a method for preparing the coating mixture according to the preamble of claim 13, the use according to claim 19 and a coated board according to claim 21.

Wall and ceiling coatings containing cellulose fibres and with a purpose to improve the acoustics are known in the construction industry.

FI 95041 and the corresponding EP 0,681,600 describe a coating mixture, a method for preparing it and the use of the mixture. The known mixture contains cotton fibre as well as CMC and a foaming agent. The mixture is prepared by mixing the CMC used as a binding agent in water and then adding the foaming agent and the cotton fibre. A sprayable mixture, which can be used for coating e.g. concrete and board surfaces, is achieved.

European Patent Application 0,759,110 describes a sound absorbing system, which is meant to be used in buildings, such as in concert halls, for indoor walls, ceilings and corresponding targets. The publication also describes the method for producing these sound absorbing systems. Correspondingly EP application 0,944,560 relates to a concrete based finishing plaster, which is meant to be used as a sound absorbing coating, as above, on inside walls and ceilings of buildings.

US 6,828,027 discloses fire proof, coated building boards, which are produced by using a coating, which contains loose material of porous particles, a silicon binding agent, a polymer dispersion, water, xanthan and optionally aluminium trihydrate.

EP application 0,165,880 discloses a method for preparation of a coating mixture meant for interior design. The known coating mixture contains cellulose fibres and/or synthetic fibres and/or mineral fibres, a filmogenic polymer and a bactericide agent. A significant disadvantage of the coating mixture used in the known art is the large amount of additives contained in these mixtures; these additives are among other things used for improving the fire resistance, the humidity resistance and the preservation of the boards and coatings. A further purpose of the additives is to produce an in beforehand chosen colour to the mixture. When added into the total mixture these additives nevertheless have an adverse effect on the mechanical properties of the coatings that are to be formed - the coatings become easily cracking and crumbling. Their adhesion properties also weaken and the mixtures become difficultly attachable to surfaces that are not completely flat.

Object of the present invention is to eliminate at least some of the disadvantages associated with the known art and to provide a new coating mixture that can readily and evenly be applied to any surfaces and that can be produced without using a large amount of harmful, expensive and complex mixtures of additives.

The invention is based on the idea that particle-like, typically mineral based filling agents are introduced into the coating mixture to produce a product with a flat surface and substantially adjustable acoustic properties. The acoustic properties of the attached layer produced from the mixture can be modified by varying the amount of these agents.

Hence the coating mixture of the present invention comprises fine cellulose or similar fibre material mixed into water and at least one binding agent, which contains e.g. carboxy methyl cellulose (CMC) or its alkali metal salt, a potato starch derivative or polyvinyl acetate or a mixture of these or a corresponding water-soluble/miscible binding agent.

Said coating mixture is prepared by mixing the fibre material and the binding agent with water using a spiral agitator optionally in the presence of a foaming agent to produce a mixture with the desired fluidity and then the optional additives, such as a boron mixture, are added and finally the particle-like filling agent.

The coating mixture according to the invention can be used to form a coating for walls and ceilings. More specifically, the coating mixture of the present invention is characterized by what is stated in the characterizing part of claim 1.

The method of the present invention on the other hand is characterized by what is stated in the characterizing part of claim 13. The use according to the invention is characterized by what is stated in claim 19 and the coated board according to the invention is characterized by what is stated in claim 21.

Substantial advantages are achieved with the present invention. Thus, the risk of undesirable chemical reactions between the coating mixture and the surface to be coated can be decreased with the help of the invention. The mixture according to the invention can provide smoother and larger surfaces compared to the known solutions. The amount of water and the amount of different additives needed to form the coating mixture is also smaller.

Another further advantage of the present invention is that it provides a coating mixture, which can be used on light materials and therefore, among other things, on materials that can be adjusted at different heights, such as on wool boards, whereas in the known art mainly gypsum boards are used as the material to be coated. The present invention also offers a faster and cheaper solution to change the acoustic properties of a room compared with the known art.

Hereinafter the invention will be viewed in more detail with the help of a detailed description and with reference to the appended drawings.

Figures Ia and Ib show a schematic view of a spiral agitator, which is used to mix the components of the coating mixture according to the invention, whereby a side view of the agitator is shown in figure Ia and a cross-section in figure Ib.

Figures 2a - 2c are graphic presentations of the absorption ratios (α_s) of mineral wool boards coated with the coating mixture according to the invention and placed against a concrete surface as a function of the frequency. Figures 3a - 3c are graphic presentations of the absorption ratios of mineral wool boards coated with the coating mixture according to the invention and placed at a distance of 200 mm from the concrete surface as a function of the frequency.

In association with the present invention "particle-like" means a powdery or finely ground filling agent, which can be mineral based or synthetic. "Finely ground" refers to an average particle size or fibre length, which generally is about 0.0001 - 50 mm, preferably about 0.01 - 50 mm, particularly preferably about 0.1 - 50 mm.

The term "mineral" or "mineral filling agent" refers to filling agents obtained from mineral material, such as limestone (GCC) or synthetic calcium carbonate (PCC). This type of filling agents contains relatively light particles, which facilitate the forming of a homogenous and smooth resulting coating mixture. Other suitable mineral filling agents are e.g. kaolin, gypsum, talc, wollastonite and calcium oxalate.

Also synthetic particles i.e. plastic particles, which e.g. can be "high filler"-type, light particles, such as plastic pellets, can be used in the mixture. Mixtures of mineral and synthetic filling agents can be used if desired. About 0.1 - 60 % by weight of the total amount of filling agent in the mixture is mineral filling agents, preferably 1 - 40 % by weight, particularly preferably 5 - 20 % by weight of the solids (the rest being fibres). 0 - 60 % of the solids can additionally consist of plastic particles.

The term "boron mixture" refers to a mixture, which contains boric acid and borax. This mixture preferably reduces the need for e.g. fire retardants or preservatives in the coating mixture.

The mixture according to the invention comprises fibre material mixed into water and a water-soluble or miscible binding agent. In addition to these components the composition contains a mineral filling agent or a similar particle-like filling agent. Fibre based on annual or perennial plants, produced by chemical or mechanical defiberization, such as cellulose or lignocellulose fibres or cotton, hemp, jute or other plant fibres can be used as the fibre material. Particularly preferable are pure cellulose fibres, such as cotton fibres and chemical pulps. The average length of the fibres is generally about 0.1 - 50 mm, preferably about 1 - 10 mm. In addition to the fibres the mixture contains a binding agent such as a cellulose or starch based, water-soluble or miscible binding agent. As examples of these, alkyl ether derivatives of cellulose, such as carboxymethyl cellulose (CMC) and its salts (e.g. sodium- CMC), as well as starch derivatives such as starch esters, starch ethers, transglycosidized starch derivatives, cationic starches, anionic starches and similar, can be mentioned. Also synthetic or mineral based binding agents, such as polyvinyl alcohol, polyvinyl acetate and silicate adhesives, such as sodium silicate, can be used. It also possible to use two or more binding agents, whereby mainly e.g. cellulose or starch based binding agents can be used as binding agent for the fibres and synthetic or mineral based binding agents on the other hand as a binding agent for the mineral filling agents.

The amount of binding agent is generally 1 - 30 % by weight, especially 3 - 15 % by weight, preferably 3 - 11 % by weight of the fibres.

The solids content of the mixture of cellulose fibre and binding agent is more than 10 % by weight, preferably 12 - 25 % by weight, particularly preferably 15 - 25 % by weight, most suitably 15 - 20 % by weight.

Only a small amount of water is needed in the mixture compared to the known art. Therefore, about 0.1 - 5 kg, especially about 1 - 2 kg H₂O / kg mixture of fibres and filling agent can be used in a mixture according to the invention.

Foaming agents can, as in the known art, be used in the coating mixture but these can partially or completely be replaced by using a mixing device, which is described in more detail below. When using a foaming agent this can e.g. be a long-chain alkyl sulphate salt, such as sodium lauryl sulphate. The amount of foaming agent is 0.001 - 0.1 % by weight of the total mixture.

Of the total amount of filling agents, the coating mixture contains 0.1 - 60 % by weight mineral filling agents, such as lime stone, as well as optionally high-fillers, the rest being cellulose fibre. The diameter (average particle size) of the limestone or corresponding mineral filling agent particles is less than about 0.5 mm, especially less than 0.3 mm. The formulation optionally also comprises fire retardants and other additives in a total amount of not more than 8 % by weight, preferably not more than 6 % by weight, calculated from the total mixture.

In addition, the formulation optionally comprises also a water softening agent, e.g. trisodium phosphate, sodium polymetaphosphate or any ion exchanger, preferably sodium tripolyphosphate, 0.0001 - 0.01 % by weight of the solids, preferably 0.0001 - 0.009 % by weight.

Based on what is disclosed above, according to one preferred embodiment of the present invention, the coating mixture contains the following components:

- fine fibre in an amount of 10 - 95 % by weight of the total mixture,

- a water-soluble binding agent, preferably carboxy methyl cellulose (CMC), potato starch or polyvinyl acetate or a mixture thereof in an amount of 1 - 30 % by weight of the fibres,

- foaming agent in an amount of 0.001 - 0.1 % by weight of the total mixture,

- mineral filling agents, such as grinded limestone, as well as optionally synthetic filling agents, such as high fillers, in a total amount of 0.1 -60 % by weight of the total amount of filling agents,

- optional additives in an amount of not more than 8 % by weight of the total mixture, and

- water.

According to another preferred embodiment of the present invention no separate foaming agent is needed. Instead, the coating mixture comprises:

- fine fibre in an amount of 10 - 95 % by weight of the total mixture,

- a water-soluble binding agent, preferably potato starch or polyvinyl acetate or a mixture thereof in an amount of 1 - 30 % by weight of the fibres,

- a mineral filling agent, such as grinded limestone, as well as optionally synthetic filling agents, such as high fillers, in a total amount of 0.1 -60 % by weight of the total amount of filling agents,

- a boron mixture, which contains boric acid and borax, for fire inhibition and preservation in an amount of not more than 8 % by weight of the solids, and

- water. The use of a boron mixture containing boric acid and borax reduces the need for use of a fire retardant or an additive. The ratio of boric acid and borax is generally between 80:20 and 20:80, preferably between 60:40 and 40:60, more preferably about 50:50, calculated by weight.

The total amount of additives, such as fire retardants, is generally not more than 8 % by weight, especially about 0.1 - 6 % by weight, of the solids of the mixture.

The coating mixtures that are prepared from these compositions have the best possible emission classification, class Ml, and they are incombustible.

The solids content of the coating mixture is typically over 10 % by weight, preferably about 15 - 35 % by weight.

According to a particularly preferred embodiment the coating mixture according to the present invention is mixed using a spiral agitator according to Figure 1. The agitator includes the following components:

1 mixing container

2 mixing nozzles

3 air nozzle

4 air tube

5 spiral part

The components of the coating mixture are fed into a mixing container 1, which is preferably made of stainless steel. The container has sidewalls and a bottom part where two types of nozzles 2, 3 are placed, to which air can be fed through a tube 4 that passes outside the container 1. The air that is fed through the mixing nozzles 2, which nozzles can be found at the edges of the bottom, provides movement in the coating pulp, whereby the components of the pulp are mixed. The air that is fed through the air nozzle 3 on the other hand provides small air bubbles when this air permeates those about 1000, preferably about 100 - 1000 holes that are situated in the nozzle 3. The bubbles create a bigger contact surface between the air and the fluid, whereby the components of the mixture dissolve more readily and produce a more homogenous and bulky mixture. The big surface and the bulkiness of the mixture are further enhanced by the spinning of the spiral part 5 of the container 1.

The air can be fed through the nozzles 2, 3 with a speed of 100 - 600 1/min.

The agitator is also suitable for transporting the prepared coating mixture or the separate components of the mixture.

The coating mixture can be prepared by a method where the finely grinded cellulose fibre and the binding agent based on cellulose or starch are mixed into water in the presence of an optional foaming agent. After this the boron mixture and the other optional additives and finally the mineral filling agent as well as the other possible additional filling agents are added.

According to a preferred application, the coating mixture is prepared by first adding the optional water softening agent and the binding agent into the water under vigorous mixing with e.g. the mixing device described above, after which the optional foaming agent, the boron mixture, the cellulose fibre and the optional additives are added, again under vigorous mixing to form an airy homogenous pulp. Finally the mineral filling agent is added also in this alternative.

The resulting mixture can be used to coat the desired surfaces to alter their acoustic properties.

If the surface that is being coated comprises boards, the coating is performed by first adding airy coating mixture to the joints of the board that is being coated and then spreading it onto the surface of the board either by spraying or by using a spatula or by first spraying the mixture onto the surface and then evening it out using a spatula. It is possible to use lighter materials, such as mineral wool plates, as the underlaying to be coated, in addition to being able to coat the conventional gypsum plates. Sound absorbing, adjustable, coated inside walls and ceilings can thus be produced. When the same mixture is applied to both the joints between the boards and to the board surfaces, there is no risk of adverse chemical reactions taking place between the jointing material and the coating agent. The process of mounting the walls and ceilings will also take less time when a coating mixture according to the invention is used both for the joints and the board surfaces. Up to 30 m² of board can be coated in an hour.

The invention also relates to sound absorbing boards that are coated with the coating mixture mentioned above. The boards are made of a light material, such as mineral wool, or conventional inside wall and ceiling material, such as gypsum, onto which the coating mixture is applied either by spraying or by using a spatula or by first spraying the mixture onto the and then evening out the coating using a spatula. A rougher and more porous coating is achieved with spraying and correspondingly a flatter and smoother coating is achieved by using a spatula. In this way surfaces corresponding to the desired smoothness grade are achieved.

In order to spray the coating mixture onto the surface of the board, a sprayer, which has at least two nozzles, preferably 2 - 5, particularly preferably 3 or 4, is preferably used. Adhesive (80 -100 % by weight of the total mixture, preferably about 90 -95 % by weight), such as sodium silicate, which optionally also contains some another binding agent (0.1 - 20 % by weight of the total mixture, preferably about 5 -10 % by weight), is sprayed from one of the nozzles and from the other nozzles coating mixture prepared according to the above.

According to the present invention it is also possible to prepare the coating mixture without binding agent. In this case the binding agent can be added to the coating mixture in the phase, where the coating mixture is sprayed onto the surface of the board by using a sprayer, which has at least two nozzles, preferably 2 - 5, particularly preferably 3 or 4. Adhesive (80 -99.9 % by weight of the total mixture, preferably about 90 -95 % by weight), such as sodium silicate, which optionally also contains some another binding agent (0.1 - 20 % by weight of the total mixture, preferably about 5 -10 % by weight), is sprayed from one of the nozzles and from the other nozzles coating mixture prepared according to the above.

The used boards that are to be coated are generally 5 - 100 mm thick, preferably 10 - 50 mm thick and most preferably 10 - 30 cm thick and a coating mixture is sprayed or applied to their surface, whereby a coating layer, which is about 1 - 30 mm, preferably about 1 - 10 mm, particularly preferably about 3 - 8 mm and most suitably about 5 mm thick, is provided.

The colour of the coating mixture is varied using colouring agents, which are bound to the fibres before the preparation of the coating mixture, instead of mixing pigments into the coating mixture, to give additional variability to the coated boards. Separately added pigments would also make the quality of the coating mixture lower by making it crack and crumble more easily. The possibility to use different colours also helps to cover the coated boards, as surfaces of desired colours are easily provided with colouring agents.

The boards according to the invention are mounted against ceilings or walls, whereby sound absorbing surfaces are provided in the spaces, where they are needed, such as in concert halls. As a board that is mounted directly against a ceiling or wall according to Examples 3 and 4 absorbs sound more effectively than a board that is mounted at a small distance from the ceiling or wall, can surfaces with adjustable absorption capacity be produced by simply attaching the boards at a mobile structure, such as a rack, with the help of which the boards can easily be moved, if required, to various small distances, preferably not more than 500 mm, particularly preferably not more than 300 mm and most suitably not more than 250 mm, from the ceiling or wall to achieve the desired absorption.

The following non-limiting examples describe the invention.

Example 1 - Preparation of the coating mixture

The coating mixture was prepared by mixing fine cellulose fibres (20 kg) and CMC 700- 2000 (1,5 kg) to water (65 - 75 litres) containing a small amount of water softening agent in the presence of sodium lauryl sulphate (4 dl). Hereafter the boron mixture (1 - 6 dl) was added together with the limestone or the high-fillers (2 - 15 kg), an optical clarifier (0 - 5 ml) and Amgard TR fire retardant (2 - 3 litres).

With the prepared mixture a flexible and resistant coating was achieved, with which smoothness was obtained that corresponded to the smoothness of a surface that only is painted. Example 2 - Preparation of a coating mixture by using a spiral agitator

Water (17 litres) containing a tablespoon of water softening agent was mixed vigorously using a small spiral agitator. CMC (DP 700-2000, 1.5 - 1.8 kg) was added to the water while mixing, after which Amgard TR fire retardant (2.5 litres) and optical clarifier (40 drops) was fed into the mixture. The thereby resulting mixture corresponded to a homogenous gel. A boron composition (2 dl) was added, after which the total mixture was poured into the container/agitator 1 made of stainless steel (Figure 1). More water (55 - 60 litres) was added and the mixing was continued while air was fed into the container 1 (100 - 1000 1/min) through the nozzles 2, 3 at the bottom of the container 1.

The mixing was continued until the gel-like mixture (thickness like bun dough) has completely dissolved in the water. Fine cellulose was then added slowly while air was still fed into the container 1 through the nozzles 2, 3. Finally 2 -15 kg finely ground limestone (average particle size < 0.3 mm), of which a part can be replaced with plastic pellets (high fillers), was fed together with polyvinyl acetate.

The use of a spiral agitator according to the invention yields a very homogenous and flexible coating mixture.

Example 3 - Measuring the absorption ratio using the reverberation room method

Three different coating mixtures were prepared according to the previous examples and by using 20 kg of fibre in each mixture. There was 10 kg of mineral filling agent in mixture 1, 6 kg mineral filling agent in mixture 2 and 3 kg mineral filling agent in mixture 3. The coating mixtures were sprayed on 20 mm thick boards (onto a surface of 11.52 m²), which were made of mineral wool, and placed directly against a concrete surface. The coating mixture that was sprayed onto the boards was evened out using a spatula to an about 5 mm thick layer.

The measurements of the absorption ratio were performed at a temperature of 16 °C at 50 % air humidity according to the standards SFS-EN ISO 354-1985 and SFS-EN ISO 11654.

The results of the measurements for the mixtures are shown in Table 1. Table 1

Graphic presentations of the absorption ratio (α_s) of the mixtures as a function of the frequency (f) are shown in Figures 2a - 2c.

According to the test results and under these measurement conditions the coating mixtures belong to absorption class B according to the standard EN ISO 11654 and according to the same standard the coating mixture 1 has under these conditions a weighted absorption ratio (α_w) of 0.8, coating mixture 2 has an weighted absorption ratio of 0.8 and coating mixture 3 has an weighted absorption ratio of 0.81, correspondingly.

Example 4 - Calculation of the absorption ratio using the reverberation room method for coated boards at a small distance from a wall or ceiling

Three different coating mixtures (mixture 1, 2 and 3) were prepared according to Example 3. The coating mixtures were sprayed on 20 mm thick boards (onto a surface of 8.64 m²), which were made of mineral wool, and placed at a 200 mm distance from the concrete surface to be covered. The coating mixture that was sprayed onto the boards was evened out using a spatula to an about 5 mm thick layer.

The measurements of the absorption ratio (α_s) were performed at a temperature of 16 °C at 50 % air humidity according to the standards SFS-EN ISO 354-1985 and SFS-EN ISO 11654.

The results of the measurements for the mixtures are shown in Table 2.

Table 2

Graphic presentations of the absorption ratio (α_s) of the mixtures as a function of the frequency (f) are shown in Figures 3a - 3c.

Under these test conditions the coating mixtures belong to absorption class C according to the standard EN ISO 11654 and according to the same standard the coating mixture 1 has under these test conditions a weighted absorption ratio (α_w) of 0.69, mixture 2 has a weighted absorption ratio of 0.73 and mixture 3 has a weighted absorption ratio of 0.75, correspondingly.

Claims

1. Coating mixture comprising

- fine fibre material mixed into water and

- a water-soluble or miscible binding agent, characterized by

- a mixture of mineral and synthetic filling agents, whereby there are mineral filling agents at about 0.1 - 60 % by weight of the total amount of filling agent in the mixture.

2. Coating mixture according to claim 1, characterized in that its solids content is over 10 % by weight, preferably 15 - 35 % by weight.

3. Coating mixture according to claim 1 or 2, characterized in that its fibre material comprises cotton fibre or cellulose fibre.

4. Coating mixture according to any of claims 1 to 3, characterized in that the amount of binding agent is 1 - 30 % by weight of the fibre material, preferably 3 - 11 % by weight.

5. Coating mixture according to any of claims 1 to 5, characterized in that it contains a foaming agent, such as the salt of a long-chain alkyl sulphate, e.g. sodium lauryl sulphate.

6. Coating mixture according to claim 5, characterized in that the amount of the foaming agent is 0.001 - 0.1 % by weight of the total mixture.

7. Coating mixture according to any of the preceding claims, characterized in that the mineral filling agent is finely ground limestone or synthetic calcium carbonate, especially limestone.

8. Coating mixture according to claim 7, characterized in that the amount of mineral filling agent is 0.1 - 60 % by weight, preferably about 1 - 40 % by weight, particularly preferably about 5 - 20 % by weight, of the total amount of filling agent.

9. Coating mixture according to any of the preceding claims, characterized in that the mixture contains additives, such as fire retardants, in a total amount of not more than 8 % by weight, especially about 0.1 - 6 % by weight, of the solids of the mixture.

10. Coating mixture according to any of the preceding claims, characterized in that it contains a boron mixture, which comprises boric acid and borax, for fire inhibition and preservation.

11. Coating mixture according to claim 10, characterized in that the boric acid and borax ratio is generally between 80:20 and 20:80, preferably between 60:40 and 40:60, more preferably about 50:50, calculated by weight.

12. Coating mixture according to claim 9, characterized in that it contains a water softening agent, e.g. trisodium phosphate, sodium polymetaphosphate or any ion exchanger, preferably sodium tripolyphosphate, at 0.0001 - 0.01 % by weight of the solids, preferably 0.0001 - 0.009 % by weight.

13. Method for preparing a coating mixture according to any of claims 1 to 12, characterized in that

- the fibre material, the binding material and the water are mixed together in the presence of an optional foaming agent to form a viscous mixture, and

- a mixture of mineral and synthetic filling agents is added to this mixture, whereby there are mineral filling agents at about 0.1 - 60 % by weight of the total amount of filling agent in the mixture.

14. Method according to claim 13, characterized in that

- in a first phase the binding agent is added to the water under vigorous mixing,

- in a second phase an optional foaming agent is added,

- in a third phase the fibre is fed into the mixture under vigorous mixing to form an airy, homogenous pulp and

- in a fourth phase the mineral filling agent is added.

15. Method according to claim 13 or 14, characterized in that solids are added in an amount that is sufficient to give the mixture a solids content, before the application, that is over 10 % by weight, preferably 15 - 35 % by weight.

16. Method according to claim 13, characterized in that in the third phase a boron mixture, which comprises boric acid and borax, is added for fire inhibition and preservation.

17. Method according to any of claims 13 to 15, characterized in that the components of the mixture are mixed together in a spiral agitator, which comprises

- a mixing container (1) with side walls and a bottom part,

- mixing nozzles (2), which are connected to the bottom part of the mixing container and through which air can be fed to mix the contents of the agitator,

- air nozzles (3), which are connected to the bottom part of the mixing container and which have small holes and through which air can be fed into a mixing tank to disperse the air into the fluid phase, and

- air tubes (4), through which air can be fed into the container (1) through the nozzles (2, 3).

18. Method according to claim 16, characterized in that 100 - 600 1 air/min is fed into the mixing container.

19. Use of a coating mixture according to any of claims 1 to 12 in a method for coating inside walls or ceilings, according to which method an airy coating mixture is applied by spraying or by using a spatula or by first spraying the coating mixture onto the surface of the wall or ceiling and then evening out the coating using a spatula.

20. Use according to claim 18 to produce sound absorbing, coated inside walls or ceilings.

21. Coated board, which can be attached to a ceiling or a wall, characterized in that it comprises a board made of a light material, such as wool, and coated with a coating mixture according to claim 1, whereby a sound absorbing material is provided.

22. Coated board according to claim 21, characterized in that it is 5 - 100 mm, preferably 10 - 50 mm and particularly preferably 10 - 30 mm thick.

23. Coated board according to claim 21 or 22, characterized in that it is coated with a coating layer, which has a thickness of about 1 - 30 mm, preferably about 1 - 10 mm, particularly preferably about 3 - 8 mm and most suitably about 5 mm.

24. Coated board according to any of claims 21 to 23, characterized in that the coating layer is applied onto the surface of the board by spraying or by using a spatula or by first spraying the mixture onto the surface of the wall or ceiling and by thereafter evening out the coating using a spatula.

25. Use of a coated board according to any of claims 21 to 24 in a method of producing surfaces on ceilings or walls having an adjustable absorption capacity, according to which method the boards are attached to a mobile structure, such as a rack, with the help of which the boards can be moved to a distance from the ceiling or wall to achieve the desired absorption.