In particular the present of invention relates to a slurry, which contains a binding agent, such as a cement slurry used for coating walls.

During the manufacture of walls and wall elements for buildings etc., the conventional method is to apply grout or plaster or alternative cementitious coating on the walls or wall elements by spraying coating material on the walls. This can be done on both exterior end interior walls. The material is then in the form of a slurry, which contains a binding agent, normally cement-based or cementitious as mentioned above, and a filler such as sand for example. In order for the slurry to adhere to the wall surface, the wall surface is usually provided with some type of reinforcement. This increases both the adhesion of the slurry to the surface and enhances the mechanical strength of the resulting coating. The reinforcement may consist of a wire mesh net, woven glass fibre fabric etc. The reinforcement is in- stalled separately, and this is naturally a cost-increasing factor in the process.

During the spraying of the slurry, special equipment is used. This equip- ment may consist of a mixer for mixing the slurry, a pipe or flexible hose for trans- porting the slurry to a mouthpiece where compressed air is added to the slurry, a compressed air source and a pump for the slurry. The compressed air is mixed with the slurry at the outlet opening of the mouthpiece, where the compressed air is added via a separate channel on the outer perimeter of the mouthpiece, in order to achieve the spray effect.

As an alternative the slurry may be applied to the wall by means of a manually driven apparatus including a container for the slurry and a manually ope- rated means for throwing and spreading the slurry onto the wall, mostly including some type of the shovel element. Also manual plastering equipment may be used, e. g. trowels etc.

In the case of using the latter type of manual equipment, it is possible to have a slurry that contains reinforcement elements, such as for example fibres.

However, the automatic equipment described above does not allow this possibility, since a slurry containing fibres will lead to congestion of the mouthpiece, and the frequent cleaning operations that are required will result in it not being economi- cally motivated to use automatic application equipment for fibre containing slurry.

The purpose of the present invention is to solve the general problem of obtaining a good mixture of a slurry and a propellent gas in any context when such a mixture is used. It is also a purpose of the present invention to solve the above described problems in particular in connection with the coating of walls with a slurry containing reinforcement elements, such as fibres.

The purpose of the present invention is achieved by the method including the advantageous features stated in the characterizing portion of claim 1, as well as by an apparatus including the advantageous features stated in the characteriz- ing portion of claim 5.

According to the inventive method, the slurry is fed into the cavity, the pro- pellent gas is added to the slurry inside the cavity, the resulting gas-added slurry is allowed to undergo a first expansion step while it is still inside said cavity, before it is allowed to exit from the cavity, and it undergoes a second expansion step while exiting from the cavity into the ambient air, whereby it is sprayed onto a de- sired object. By mixing the slurry and the propellent gas inside the cavity, prior to the spraying, a first expansion step can be achieved in the cavity, offering a vol- ume which is considerably larger than the relatively narrow passages available when the expansion takes place in the opening of an ordinary mouthpiece. Con- sequently, it will become possible to use a slurry mixed with particles or elements that are considerably larger than the filler elements, such as reinforcement ele- ments or elements used in view of obtaining a specific surface structure.

The expansion in two steps will occur since the propellent gas cannot ex- pand directly to the external air pressure. This is due to the fact that the slurry pre- sent between the gas outlet and the gas/slurry outlet in the cavity will function more or less as a plug, and prevent an immediate complete expansion of the gas.

To continue, due to the expansion of the mixture in two steps, the slur- ry/gas mixture leaving the mouthpiece will have a conical shape and the slurry will be finely"atomized", thus achieving a superior spray effect. The slurry can thus be

sprayed in thin layers, which improves the drying process and decreases the risk for cracking. In addition, this has the advantage that a certain evaporation takes place, which also reduces the time required for drying.

The inventive apparatus, according to the present invention, includes a cavity surrounded by a cavity wall and in which cavity the propellent gas and the slurry are mixed, further containing an inlet opening in the cavity wall for feeding the slurry into the cavity, means for feeding the propellent gas into the cavity, whereby the slurry is brought to a first expansion step inside the cavity by the add- ing of the propellent gas to the slurry, and further including means for spraying the gas and slurry mixture onto a desired object, during a second expansion step. The advantages achieved by this apparatus correspond to the advantages above, mentioned in connection with the inventive method.

Advantageously, the slurry contains a binding agent, preferably a hydrau- lic binding agent, for example cement, and also a filler, such as sand, cinder, fly ash etc. The slurry may also contain reinforcement elements, which may be or- ganic or inorganic. Examples of such elements are vegetable fibres in the form of soaked cutter shavings, straw, chaff, strips of corrugated cardboard or paper, etc.

The slurry may also contain particles or elements, which gives the coating surface a certain structure, such as sand particles or gravel, plastic granules, etc.

Advantageously, the means for feeding the propellent gas into the cavity include a tube connected to a gas source, and which is inserted through the wall of the cavity and is moveable inside the cavity, and has a gas outlet opening in- side the cavity. In a preferred embodiment, the tube is moveable in different posi- tions inside the cavity. These positions are chosen depending on the properties of the slurry fed into the cavity. Preferably, the apparatus also includes means for adjusting the position of the tube inside the cavity.

Further features and advantages will become apparent from the depend- ent claims.

The present invention will now be described in further detail, with refer- ence to different embodiments, given by way of example only, illustrated in the appended schematic drawings, in which:

Figure 1 shows a side view, partially in cross section, of a first embodiment of an apparatus according to the present invention: Figure 2 shows a side view, partially in cross section, of a second embodi- ment of the apparatus, according to the present invention, Figure 3 shows a side view, partially in cross section, of the second embodi- ment; Figure 4 shows a side view, partially in cross section, of the second embodi- ment; Figure 5 shows a side view, partially in cross section, of a third embodiment of the apparatus, according to the present invention; and Figure 6 shows a side view, partially in cross section, of a fifth embodiment of the apparatus, according to the present invention.

In the first embodiment of the apparatus illustrated in figure 1, the appara- tus comprises a cavity 1 into which a slurry is fed through a inlet opening 3 and propellent gas is fed into the cavity via a gas feeding means 5. The gas feeding means comprises a tube 6 inserted through the wall 8 of the cavity and having an outlet opening inside the cavity. The tube is connected to a compressed propellent gas source, not illustrated. The slurry inlet opening 3 is located at the bottom of a funnel shaped container 10, into which the slurry is fed. The slurry itself has al- ready been previously mixed in a separate mixer. The cavity 1 has an outlet open- ing 4 for the gas and slurry mixture. In the illustrated first embodiment the gas/slur- ry outlet opening is designed as a mouthpiece with an essentially cone-shaped design. This outlet for the gas/slurry mixture, or spray outlet, has an opening with an area (SOA) in relation to the area of the gas outlet opening (GOA) which pref- erably is in the interval of 10 to 30 times the latter.

The tube 6 is moveable in such a way that it can adopt different positions within the cavity. This is more clearly illustrated in figures 2-4. The opening of the tube is directed towards the gas/slurry outlet 4. The tube can in fact also be re- movable, in order to facilitate cleaning of the tube and the outlet opening of the tube.

A second embodiment of the apparatus according to the present invention is illustrated in figures 2-4. This embodiment mainly differs from the first embodi-

ment in that the slurry is not fed into the cavity via a funnel-shaped container. In- stead, the slurry is fed by means of a tube or pipe 20 directly connected to the cavity 1 by means of an inlet opening 13. The tube 20 preferably has the same di- ameter as the diameter of the cavity 11. The means for feeding the propellent gas 15 into the cavity 20 comprise a tube 16 inserted through an opening in the cavity wall 18. The tube is moveable and can adopt different positions inside the cavity, as illustrated in figure 3 and figure 4. In the position adopted by the gas inlet tube illustrated in figure 3, the apparatus is particularly suitable for a slurry containing fibres or other reinforcement elements. As can be seen, this position is a position where the tube 16 is in a rearward position, i. e. with its outlet relatively close to the cavity wall. The gas fed into the cavity 11 mixes with the slurry fed into the cavity via the inlet 13 and the gas/slurry mixture undergoes an essentially cone-shaped, first, partial expansion step, illustrated by the cone 22. The mixture is then pro- pelled towards the outlet of the cavity 14, where it undergoes a second expansion step, illustrated by the cone 23 in figure 3.

Figure 4 illustrates the apparatus according to the second embodiment when it is adapted to a slurry, which contains little or no fibre. For this purpose the gas inlet tube 16 is inserted further inside the cavity 11, i. e. with its outlet further forward, in the direction towards the outlet for the gas/slurry mixture, then the po- sition illustrated in figure 3. Also in this case, the slurry and the gas are mixed in an essentially cone-shaped expansion, illustrated by the cone 32. This is also a partial expansion, in a first expansion step. The mixture is then directed towards the outlet of the cavity, where it undergoes a second expansion illustrated by the cone with the reference number 33. It is during the second expansion that the slurry is sprayed onto the surface, which is to be coated by the slurry material.

A third embodiment is illustrated in figure 5. This only differs from the em- bodiment in figure 4, in that the outlet opening 34 for the gas and slurry mixture has a much less accentuated conical form. This allows for the spraying of a slurry containing much larger reinforcement particles or other particles or fibres. This slurry is fed into the cavity 31 via a tube 40 with the same diameter as the cavity, and the gas is fed into the cavity 31 by means of a feeding device 35, designed as a tube 36. In this figure is also illustrated means for controlling the feed of the pro-

pellent gas into the cavity. Said control means may comprise a valve, not illus- trated, and a pressure gauge 39. By controlling the gas flow and the gas pressure it is possible to control the flow of slurry through the cavity, as well as the charac- teristics of the spray jet. For example, if the pressure is too high, the impact veloc- ity of the spray against the surface will be too high, which will result in that larger particles in the slurry will bounce off the surface. The pressure must also be adapted to the friction of the slurry within the cavity. The gas pressure inside the tube may be in the interval 150 kPa-700 kPa, preferably approximately 200 kPa.

In the fourth embodiment illustrated in figure 6, the outlet opening of the cavity 51 is not cone-shaped. Instead it has essentially the same diameter as the cavity itself and it also has essentially the same area as the slurry inlet opening 40 of the cavity. The gas feeding means 45 are arranged in an opening in the cavity watt, in a way similar to what has been described above.

The present invention shall not be considered as limited to the embodi- ments above, given by the way of example only, but may be varied and modified in numerous ways by the persons skilled in the art, within the scope of the ap- pended patent claims.