ZA200710726B

ZA200710726B - A method of rendering a wall surface

Info

Publication number: ZA200710726B
Application number: ZA200710726A
Authority: ZA
Inventors: Human Johan Leonard
Original assignee: Imison Proprietary Ltd
Priority date: 2006-09-18
Filing date: 2007-12-10
Publication date: 2008-11-26

Description

-2- pm 2007/7 19724

A METHOD OF RENDERING A WALL SURFACE

THIS INVENTION relates to a method of rendering a wall surface. ~ FIELD OF INVENTION

The method relates particularly to a method of rendering a wall surface using cement slurry.

SUMMARY OF INVENTION

According to the invention there is provided a method of rendering a wall surface using cement slurry, the method including: placing mesh against a surface defined by a wall; and by means of a hand held slurry spraying device, spraying cement slurry through the mesh onto the wall surface and onto the mesh to embed the mesh and to form a cover layer of cement slurry over the mesh.

The Applicant envisages that the method of the invention may be particularly suitable for rendering a wall that has an uneven surface, defining peaks and depressions. In this case, the method may include: placing the mesh against the peaks and spanning across the depressions; and spraying the cement slurry through the mesh into the depressions, filling the depressions.

In the said case, the mesh, when placed, may define a substantially even plane over the wall surface with gaps being defined between the mesh and the wall surface at the depressions. The cement slurry is then sprayed through the mesh into the depressions, filling the depressions. It is thus important that the consistency of the cement slurry, particularly its workability, is such that it can pass through the mesh to fill up the depressions without unduly deflecting the mesh into the depressions. The method is preferably executed with the mesh remaining as undeflected as possible after completion of the spraying of the cement slurry. With a substantially even cover layer of cement slurry formed over the mesh, the surface of the cover layer follows the shape of the mesh and is thus substantially even.

The mesh used in the method of the invention, at least to some extent, retains the cement slurry being sprayed and provides a reference for a workman spraying the cement slurry, thus facilitating spraying of the slurry to a substantially even surface, requiring only final finishing. A significant advantage of the method of the invention is thus that it does not require “levelling” using a straight edge or a long trowel, as is often required with conventional rendering methods. The method thus, in a sense, achieves “self-levelling” of the cement slurry.

The method may include a step of wetting the wall surface prior to spraying cement slurry onto it.

The method may include:

spraying a layer of cement slurry onto the wall surface to define a new, uneven wall surface prior to locating the mesh against the new wall surface; and pressing the mesh into peaks defined by this layer to adhere the mesh to the layer.

The mesh may be made of any suitable material, provided that the material of the mesh must be alkali-resistant or have an alkali-resistant coating. The mesh may, for example, be a steel strand mesh, with a strand gauge of between 0.25 and 0.5mm being suitable for many applications of the method, a woven fibreglass mesh, or, for some applications, a plastic mesh. The aperture size of the mesh may be in the range 9 to 225mm?2. To ensure “continuity” of the mesh used in the method, the method may include overlapping adjacent mesh sheets.

The Applicant envisages that, for use in the method of the invention, cement slurry with a water/cement ratio exceeding 0.45 may be particularly suitable. In order to obtain the required workability in some types of cement slurry, an additive may be used. The additive may include a polymer and the Applicant envisages that, in most slurries requiring an additive to obtain the required workability, a polymer content not exceeding 2% of the weight will be sufficient. Suitable alternative additives may be used, for example a plasticizer.

The cement slurry may include reinforcing fibres. The fibres may be made of polypropylene. The length of the fibres may vary according to the configuration of the slurry spraying device. The Applicant proposes a fibre length of between 4 and 16mm.

The method may include finishing the surface of the cover layer of cement slurry using conventional finishing means, for example at least one of a trowel and a sponge.

The cement:sand ratio of the cement slurry may vary according to the application.

Generally, a ratio of 1:5 should be suitable, say between 1:4 and 1:7. For the final layer, finishing may be facilitated by using slurry with a cement:sand ratio of 1:6. For use of the method on some surfaces, e.g. ones defined by expanded polystyrene or smooth concrete surfaces, a strong base layer may be formed using cement slurry with a cement:sand ratio of between 1:2 and 1:3.

The cement may, of course, be Portland cement.

The sand used is preferably, but not necessarily, graded sifted sand.

The method may be used to define a neat corner of a wall, be it an inner or an outer corner. In order to define such a corner, a mesh sheet to be used at the corner may be ~ bent to define a bend having an angle required for the corner, in most cases 90°. The mesh is then placed with its bend along the corner to be rendered. The cement slurry is then sprayed through and over the mesh, in accordance with the method of the invention, until a cover layer is formed over the mesh and around the corner. The cover layer then is finished, typically using a corner trowel at the very corner.

The hand held slurry spraying device used in the method may include: an open-topped container for holding the cement slurry, the container defining an outlet opening near a lower end thereof through which the cement slurry can be discharged from the container; and a discharge pipe having a substantially L-shaped pipe section that extends from the outlet opening of the container for discharging cement slurry from the container, the pipe section including a discharge nozzle which defines a discharge nozzle inlet opening through which cement slurry can enter the discharge nozzle and a discharge nozzle outlet opening through which cement slurry can be discharged from the discharge nozzle, the pipe section defining a gas inlet opening through which a propellant gas can be introduced into the discharge pipe for propelling cement slurry through the discharge nozzle, the gas inlet opening and the discharge nozzle outlet opening being aligned concentrically.

The container of the slurry spraying device may be in the form of a funnel-shaped hopper for feeding cement slurry into the discharge pipe under the influence of gravity.

The gas inlet opening may be configured to receive a gas pipe having a discharge opening, for operatively conveying a propellant gas into the cement slurry. The discharge opening may have a diameter not exceeding 6mm. The propellant gas may be air. For spraying the cement slurry, an airflow not exceeding 300L/min may suffice.

The slurry spraying device may include a reduction nozzle defining a reduction nozzle outlet opening, which may have a diameter in the range 6 to 18mm.

Further features of the invention are described herein after by way of a non-limiting example of the invention, with reference to and as illustrated in the accompanying diagrammatic drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a side view of a hand-held cement slurry spraying device for use in a method of rendering a wall surface using cement slurry, in accordance with the invention;

Figure 2 shows a sectional side view of the device of Figure 1, showing an exploded view of the reduction nozzle;

Figure 3 shows a part sectional elevation of a wall defining an uneven wall surface;

Figures 4 to 7 show the wall section of Figure 3 in consecutive stages of rendering, in accordance with a method of rendering a wall surface using cement. slurry, in accordance with the invention; and

’ Fos: -7- =20 0

Figure 8 shows a corner defined by the wall, the surface of the wall around the corner having been rendered in accordance with the method of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to Figures 1 and 2 of the drawings, a hand-held slurry spraying device for use in the method of rendering a wall surface using cement slurry, in accordance with the invention, is designated generally by the reference numeral 10.

The spraying device 10 is of fabricated stainless steel and comprises, broadly, a container in the form of an open-topped hopper 12 and a discharge pipe designated generally by the reference numeral 14.

The hopper 12 is funnel-shape and defines an outlet opening 16 in a base region thereof, through which cement slurry can be discharged from the hopper into the discharge pipe 14. The hopper has a handle 18 by which it can be held in use.

In use, cement slurry can be introduced by hand using, for example, a trowel into the hopper 12 and can then be fed into the discharge pipe 14 under the influence of gravity via the outlet opening 16 in the base of the hopper.

The discharge pipe 14 includes an L-shaped pipe section 20, which extends from the outlet opening 16 of the hopper, and a reduction nozzle 22. The pipe section 20 defines a discharge nozzle 24. The pipe section 20 includes adjustable holding means in the form of a holding formation 26 defining an internal passage 27 in which a gas pipe (not shown) for conveying a propellant gas such as air, can be received. The holding formation 26 defines a gas inlet opening 28 at the end of the passage 27, which leads into the pipe section 20.

The gas pipe is connectable to a supply of air and defines a passage with ‘a diameter typically not exceeding 6mm therethrough and a discharge opening at an end of the passage, operatively exposed to the inside of the pipe section 20.

The holding formation 26 includes a screw 30 which can be releasably screwed onto an outer surface of the gas pipe, in use, for securing the gas pipe within the holding formation. The gas pipe is thus slideably displaceable within the internal passage 27 of the holding formation 26 in an arrangement wherein the position of the gas pipe within the holding formation can be adjusted. Once a desired position has been achieved, it can be secured in place by means of the screw 30. Hence, the position of a discharge opening of the gas pipe can be adjusted relative to the reduction nozzle 22. The reason for this feature will be explained hereinafter.

The discharge nozzle 24 is formed integrally with the pipe section 20 and has a frusto- conical configuration. More particularly, the discharge nozzle has a nozzle inlet opening 32 and a nozzle outlet opening 34. The nozzle outlet opening 34 is eccentric with respect to the nozzle inlet opening 32 in an arrangement wherein the centreline of the : nozzle outlet opening is disposed operatively lower than the centreline of the nozzle inlet opening.

The nozzle outlet opening 34 of the discharge nozzle 24 is aligned concentrically with the gas inlet opening 28, thereby providing for the propellant gas to enter the discharge pipe directly behind the slurry and in alignment therewith. In the drawings, axis A passes through the concentrically aligned centres of the nozzle outlet opening 34 and the gas inlet opening 28. This configuration generates a “back pressure” in the discharge pipe, resulting in an increase in the pressure of the propellant gas upstream of the cement slurry for more effective propulsion of the slurry in the slurry spraying device.

In use of the device 10, the position of the gas pipe can be adjusted so as to vary the distance between its discharge nozzle and the reduction nozzle 22. Through such adjustment, the spread of a cement slurry spray ejected from the nozzle 22 can be adjusted.

The pipe section 20 includes a connector flange 36 defining an external screw-thread formation and defining therein a seat formation complementary to a matching seat formation defined by the reduction nozzle 22. The seat formation of the reduction nozzle 22 includes an outer collar 40 defining a frusto-conical outer surface. The device 10 includes also a collar 42, which defines an internal screw-thread matched to the screw- thread of the connector flange 36, for cooperating with this flange and the collar 40 for securing the reduction nozzle 22 to the connector flange 36.

The reduction nozzle 22 defines a large reduction nozzle inlet opening 44 and a small reduction nozzle outlet opening 46, the latter having a diameter in the range 6 to 18mm.

In use of the device 10, cement slurry in the hopper 12 is fed into the discharge pipe 14 under the influence of gravity via the outlet opening 16 in the base of the hopper.

Propelled by air ejected from the discharge outlet of the gas pipe, a mixture of air and cement slurry is thus ejected through the opening 46 of the reduction nozzle 22.

In Figure 3, a wall 48 is partially shown, in cross-section. The wall 48 is constructed of cement blocks 50, of which only four are shown, with layers of cement 52 in between them. The wall 48 defines a wall surface 54, which is uneven. Rendering of the wall surface 54, in accordance with the method of rendering a wall surface using cement slurry, in accordance with the invention, will now be described with reference to Figures 3to7.

Still in Figure 3, in accordance with the method of the invention, first, the wall surface 54 is wetted, if porous. If non-porous (e.g. polystyrene) then no wetting is required

In Figure 4, using the hand-held slurry spraying device 10 of Figures 1 and 2, a layer of cement slurry 56 has been sprayed onto the wall surface 54 to define a new uneven wall surface 58.

The cement slurry used for this purpose may, for example, be a 1:5 Portland cement: sand mix. Cement:sand ratios of between 1:4 and 1:7 may be tried for different conditions.

In Figure 5, a sheet of alkali-resistant mesh 60 has been located on the wall 48, particularly by pressing it into the wet cover layer 56 at locations where the wall 48 defines peaks 62. The mesh 60 may, for example, be a woven fibreglass mesh, a steel strand mesh having an alkali-resistant coating, or even a plastics mesh. The aperture size of the mesh used may vary in practice and will typically be in the range from 9 to a 225mm?2. In the case of steel strand mesh, the strand gauge may be in the range 0.25 to 0.5mm.

The mesh 60 is maintained substantially planar and, as such, defines an even surface.

The mesh 60 spans across a depression 64 defined between the peaks 62 with a gap 66 being defined between the mesh 60 and the wall surface 58 at the depression 64. It will be understood that the mesh 60 extends beyond the view shown in the upward and downward direction and also extends longitudinally along a length of the wall 48. As such, it is also in contact with other peaks defined by the wall 48 and spans across other depressions defined between the peaks. The example method will be further described with reference particularly to the features of the wall 48 shown, it being understood that the same applies to a surrounding portion of the wall.

In Figure 6, using the device 10 of Figures 1 and 2, the gap 66 has been filled by spraying cement slurry through the apertures defined in the mesh 60 and, as such, has been filled with cement slurry 68. The slurry used at this stage stillis a 1:5 mix.

By further spraying of cement slurry, a cover layer 70 of the slurry 68 has been formed over the mesh 60. The slurry used at this stage may, for example, be a 1:6 mix. The cover layer 70 defines an uneven surface.

In Figure 7, the surface of the cover layer 70 has been finished to a smooth surface using a trowel and, optionally, a floating sponge.

Throughout the spraying of the cement slurry onto the wall 48, the mesh 60 remains substantially in the same position. After finishing, the surface of the cover layer 70 follows the shape of the mesh 60 and is thus substantially even.

In order to avoid the cement slurry spray from unduly deflecting the mesh 60 into the depression 64, sufficient workability of the slurry must be ensured. The Applicant has found cement slurry with a water/cement ratio exceeding 0.45 to be particularly suitable for use in the method. A suitable additive may also be mixed into the cement slurry for achieving a required workability and the Applicant has found that, in some slurries, a polymer content of approximately 20g/kg yielded the required workability. Alternatively, a plasticizer may be used.

The cement slurry may include reinforcing fibres, for example polypropylene fibres, for reducing shrinkage crack formation. For the device 10, the Applicant has found a fibre length of between 4 and 16mm to be particularly suitable.

For propelling most suitable types of cement slurry, the Applicant has found that an air flow not exceeding 300L per minute at a pressure of Sbar was sufficient.

In Figure 8, the surface 54 of the wall 48 around a corner 74 defined by the wall has been rendered using the rendering method of the invention. For this purpose, a sheet of mesh 76 was bent through 90° before placing it around the corner 74. As such, the method facilitated achieving a neat 90° corner surface. Final finishing has been done using a corner trowel and a floating sponge.

To ensure “continuity” of the mesh used in the method described above, the mesh sheets used in the method of the invention are overlapped by approximately 100mm.

The method may be applied to a wall defining a smooth surface, e.g. an expanded polystyrene or a smooth concrete wall. In this case, a strong base layer may be formed using cement slurry with a cement:sand ratio of between 1:2 and 1:3.

The Applicant submits that the method of the invention is efficient in finishing any of a variety of different wall surfaces including ones defined by brick, cement blocks, concrete, and expanded polystyrene walls. Particularly in the case of an uneven wall surface, the Applicant has found that the method required less skill than some existing methods for achieving a high standard of finish. The same applies to a corner defined by a wall.

Claims

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1. A method of rendering a wall surface using cement slurry, the method including: placing mesh against a surface defined by a wall; and by means of a hand held slurry spraying device, spraying cement slurry through the mesh onto the wall surface and onto the mesh to embed the mesh and to form a cover layer of cement slurry over the mesh.

2. A method as claimed in claim 1, which is applied to a wall that has an uneven surface, defining peaks and depressions, the method including: placing the mesh against the peaks and spanning across the depressions; and spraying the cement slurry through the mesh into the depressions, filling the depressions.

3. A method as claimed in any preceding claim, including wetting the wall surface prior to spraying cement slurry onto it.

4. A method as claimed in any preceding claim, including: spraying a layer of cement slurry onto the wall surface to define a new, uneven wall surface prior to locating the mesh against the new wall surface; and pressing the mesh into peaks defined by this layer to adhere the mesh to the layer.

5. A method as claimed in any preceding claim, in which the mesh is made of an alkali-resistant material or has an alkali-resistant coating.

6. A method as claimed in any preceding claim, in which the mesh is a steel strand mesh, a woven fibreglass mesh, and a plastic mesh.

7. A method as claimed in claim 6, in which the mesh is a steel strand mesh having a strand gauge in the range 0.25 to 0.5mm.

8. A method as claimed in any preceding claim, in which the mesh is defined by overlapping adjacent mesh sheets. So

9. A method as claimed in any preceding claims, in which the cement slurry has a water/cement ratio exceeding 0.45.

10. A method as claimed in any preceding claim, in which the cement slurry includes at least one additive for enhancing its workability.

11. A method as claimed in claim 10, in which the at least one additive includes a polymer.

12. A method as claimed in any one of claims 10 to 11, in which the at least one additive includes a plasticizer.

13. A method as claimed in any preceding claim, in which the cement slurry includes reinforcing fibres.

14. A method as claimed in claim 13, in which the fibres are made of polypropylene.

15. A method as claimed in any one of claims 13 to 14, in which the fibres have a length of between 4 and 16mm.

16. A method as claimed in any preceding claim, including finishing the surface of the cover layer of cement slurry using conventional finishing means such as a trowel or a sponge.

17. A method as claimed in any preceding claim, including forming a rendering layer using a cement slurry having a cement:sand ratio of between 1:4 and 1:7.

18. A method as claimed in any preceding claim, which is applied to a wall defining a smooth surface, including forming an initial rendering layer using a cement slurry with a cement:sand ratio of between 1:2 and 1:3.

19. A method as claimed in claim 18, in which the smooth surface is defined by a wall made of one of concrete and polystryrene.

20. A method as claimed in any preceding claim, in which the sand of the cement slurry is graded sifted sand.

21. A method as claimed in any preceding claim, including: providing a mesh sheet bent to define a bend having an angle corresponding to that of a wall corner to be rendered, whether an inner or an outer corner; placing the mesh sheet with its bend along the corner to be rendered; and spraying the cement slurry through and over the mesh, in accordance with the method of the invention, until a cover layer is formed over the mesh and around the corner.

22. A method as claimed in claim 21, including finishing the corner using a corner trowel.

23. A method as claimed in any preceding claim, in which the hand held slurry spraying device includes: an open-topped container for holding the cement slurry, the container defining an outlet opening near a lower end thereof through which the cement slurry can be discharged from the container; and a discharge pipe having a substantially L-shaped pipe section that extends from the outlet opening of the container for discharging cement slurry from the container, the pipe section including a discharge nozzle which defines a discharge nozzle inlet opening through which cement slurry can enter the discharge nozzle and a discharge nozzle outlet opening through which cement slurry can be discharged from the discharge nozzle, the pipe section defining a gas inlet opening through which a propellant gas can be introduced into the discharge pipe for propelling cement slurry through the discharge nozzle, the gas inlet opening and the discharge nozzle outlet opening being aligned concentrically.

24. A method as claimed in claim 23, in which the container of the slurry spraying device is in the form of a funnel-shaped hopper for feeding cement slurry into the discharge pipe under the influence of gravity.

25. A method as claimed in any one of claims 23 to 24, in which the gas inlet opening is configured to receive a gas pipe having a discharge opening, for operatively conveying a propellant gas into the cement slurry.

26. A method as claimed in claim 25, in which the discharge opening has a diameter not exceeding 6mm.

27. A method as claimed in any one of claims 23 to 26, in which the propellant gas is air.

28. A method as claimed in claim 27, in which the air has an operative flow rate not exceeding 300L/min.

29. A method as claimed in any one of claims 23 to 28, in which the slurry spraying device includes a reduction nozzle defining a reduction nozzle outlet opening.

30. A method as claimed in any one of claims 23 to 29, in which the reduction nozzle outlet opening has a diameter in the range 6 to 18mm. :

=2007/ 10726

31. A method as claimed in any one of the preceding claims, substantially as described herein with reference to the drawings. DATED THIS 10" DAY OF DECEMBER 2007 ! / ADEIAS & ADAM APPLICANTS PATENT ATTORNEYS