GB2029765A

GB2029765A - Method of Coating Surfaces of Buildings

Info

Publication number: GB2029765A
Application number: GB7924274A
Authority: GB
Original assignee: CARRS PAINTS Ltd
Current assignee: CARRS PAINTS Ltd
Priority date: 1978-07-12
Filing date: 1979-07-12
Publication date: 1980-03-26
Also published as: GB2029765B

Abstract

A method of coating a surface of a building or of a building component which involves the use of a continuous mesh having interstices of a predetermined size and a settable paste comprising liquid binder and aggregate of predetermined sizes small than the interstices of the mesh, the method comprising the steps of applying the paste to the surface to form a layer of a depth greater than the thickness of the mesh, placing the mesh against the external surface of the layer and pressing it into the layer whereby, as a result of the predetermined relationship between the sizes of the interstices and the aggregate, paste including aggregate flows into the interstices of the mesh so that the coating thus formed comprises a homogeneous mass of paste extending behind and into the interstices of the mesh which is thereby embedded in it, and then allowing the paste to set. The mesh may be pressed completely into the layer of paste so that the coating has a continuous outer surface or a second coating may be applied.

Description

SPECIFICATION Method of Coating Surfaces of Buildings This invention relates to the formation of coatings on surfaces of buildings and of components for use in the construction of buildings, for the purpose of protecting the surfaces and/or providing the surfaces with a decorative finish.

The invention has been developed primarily in connection with the coating of plywood but there is no limitation in this regard as the invention is also applicable to the coating of surfaces formed by other building materials such as, for example, bricks, breeze blocks, concrete, hardboard and chipboard.

In the case of plywoods, particulariy those made from timber having poor dimensional stability with respect to moisture content, which provided external surfaces of buildings, a problem which is encountered is that of preventing socalled "checking", i.e. grain-orientated splitting of the surface veneer which can be caused by damp penetrating the surface coating and sudden temperature changes.

There are various surface coating methods currently in use but they have various disadvantages.

In one known method Kraft paper is adhered to the surface by a phenolic resin using heat and pressure. This method can only be used in a factory to produce pre-coated plywood panels for assembly on site. If both sides of a panel are not coated, the panel is susceptible to bowing, and any surface piercing of the panel, for example by a mechanical fixing securing the panel to a building framework, may permit moisture to penetrate the piywood and cause swelling. The paper does not bridge butt joints between adjacent assembled panels so that moisture can penetrate the plywood at these locations. Another disadVantage is that a decorative finish has to be applied to the coating in a separate operation.

Another known method involves the use of fibre-reinforced paints but the coating produced thereby is ineffective in combatting "checking" of plywood and does not provide an effective "scrim" for butt joints.

In another method glass-reinforced polyester resins are used. This method cannot be used on site and the coating produced thereby has a very low moisture permeability which, in the case of a plywood panel, can result in a susceptibility to bowing if the panel is coated on one side only, and problems arising from accidental damage to the surface allowing the ingress of moisture which might be trapped. Butt joints require special treatment and subsequent decoration is necessary. In the case of an assembly of panels, a monolithic appearance cannot be obtained with this method.

In another known method a mesh is embedded in a coating produced by successively applied layers of a synthetic render but this method is time consuming and laborious. The method is unsuitable for the coating of plywoods and subsequent decoration is required.

The object of the present invention is to provide an improved method of coating surfaces of buildings and of building components, which in particular provides a coating which is effective in preventing "checking" of plywood, and does not have the disadvantages of the known methods described above.

According to a first aspect of the invention, there is provided a method of coating a surface of a building or of a building component which involves the use of a continuous sheet material formed with interstices of a predetermined size and a settable paste comprising liquid binder and aggregate of a predetermined size or sizes smaller than the interstices of the sheet material, the method comprising the steps of applying the paste to the surface to form a layer of a depth greater than the thickness of the sheet material, placing the sheet material against the external surface of the layer and pressing it into the layer whereby, as a result of the predetermined relationship between the sizes of the interstices and the aggregate, paste including aggregate flows into the interstices of the material so that the coating thus formed comprises a homogenous mass of paste extending behind and into the interstices of the sheet material which is thereby embedded in it, and then allowing the paste to set.

By a homogenous mass of paste is meant a mass of paste in which the aggregate is regularly distributed throughout the binder so that there is aggregate not only in the binder which has remained behind the sheet material but also in the binder which has flowed into the interstices of the sheet material. This is achieved by judiciously selecting aggregate of a particular size or sizes for the paste, and sheet material having interstices of a particular size so that aggregate can flow with binder into the interstices. If the interstices were too small in relation to the size of the aggregate, aggregate could not flow into the interstices with the result that the interstices would contain only binder and the cohesion of the paste and the sheet material would be impaired.If the interstices were too large in relation to the size of the aggregate, the sheet material would not provide a satisfactory reinforcement for the coating.

A second coating may be applied to the coating particularly if at least some parts of the sheet material have been left exposed. This second coating may be applied immediately after pressing of the sheet material into the layer of paste, or after the first coating has partially set so that a skin has formed on its exposed surface, or, as is preferred, after the first coating has completely set.

The second coating is preferably formed 'from a settable paste similar to the paste used for the first coating, i.e. comprising a liquid binder and aggregate. The particles of aggregate may be of the same size or sizes as the aggregate in the paste used for the first coating, or they may be larger or smaller. Alternatively, any other appropriate material may be used to form the second coating.

The paste used for the second coating may be pigmented to provide colour and durability. As the second coating is applied its outer surface may be formed into a decorative finish, for example a stippled finish.

The sheet material may be pressed completely beneath the surface of the coating so that paste including aggregate flows through the interstices in the material to form a layer of a homogeneous mass of paste covering the material whereby the coating has a continuous outer surface. In this event a second coating is not necessary.

According to a second aspect of the invention, therefore, there is provided a method of coating a surface of a building or of a building component which involves the use of a continuous sheet material formed with interstices and a suitable paste comprising aggregate and liquid binder, the method comprising the steps of applying the paste to the surface to form a layer of a depth such that the sheet material can be completely embedded therein, placing the sheet material against the external surface of the layer, the paste and the sheet material being such that on pressing of the material into the layer of paste, paste including aggregate flows through the interstices of the material whereby the coating thus formed comprises a homogeneous mass of paste having a continuous outer surface and with the sheet material embedded in it, and then allowing the paste to set.

This method involves only one application of paste to the surface to be coated and the sheet material is completely embedded within the coating so that there is no need for any further coating.

The method may include, after pressing of the sheet material into the layer of paste and prior to setting of the coating, forming the outer surface of the layer into a decorative finish, for example a stippled finish. Thus, there is no need for a subsequent, separate decorating operation. In this event, the paste is pigmented to provide colour and durability.

In both methods the paste preferably contains no more that 30% by volume of aggregate. The aggregate preferably consists of particles which are no more than 2mm in size. Usually the aggregate will contain particles of different sizes.

The liquid binder may be in the form of a solution or a suspension. Preferably the paste has nonvolatile content of between 30% and 86% by weight.

The coat weight of the paste may be between 1 and 5 kg. per sq. metre, preferably between 1.5 and 3.5.

The interstices of the sheet material are preferably of a size between one and four times the maximum aggregate size. The material may be woven or non-woven mesh of an organic or inorganic, natural or synthetic material.

The sheet material is preferably pressed into the layer of paste by means of a roller which is rolled over the whole surface of the layer to ensure that the sheet material is completely pressed into it. This roller may be formed to provide the surface of the coating with a decorative finish.

Two methods according to the invention will now be described in detail by way of example, these being applied to the coating of plywood.

In both methods the plywood may be primed or unprimed.

A layer of a paste is first applied to the surface of the plywood, the paste including aggregate and a liquid binder. The paste is adapted to set by air drying by evaporation and/or oxidation or by internal crosslinking or coalescence. The paste has a non-volatile content of about 82% by weight.

The aggregate is calcium carbonate (although it may be based on other inorganics, for example silicates, or on organics, for example cellulosics).

The aggregate comprises particles of different sizes up to a maximum of 2 mm. The binder comprises an internally plasticised co-polymer dispersed in a carrier, for example either solvent (such as water) carried as a solution or in the form of a suspension such as an emulsion or colloid.

The paste also includes extenders and/or pigments. The paste may be applied by spray, brush, roller or pad.

A fibrous mesh of suitable fibre length, orientation and durability is then placed against the external surface of the layer of paste. The composite fibres may be (a) organic and natural, e.g. cotton (cellulosic), or (b) organic and synthetic, e.g. Terylene (Registered Trade Mark) or Nylon, or (c) inorganic and natural, e.g. natural glass, or (d) inorganic and synthetic, e.g.

fabricated glass or carbon filament. The mesh mag be woven with or without weave locking and sizing, or non-woven with or without sizing and with random fibre orientation or, as is preferred, direction orientation, the mesh being disposed so that the fibres which extend in one direction, are arranged transversely with respect to the grain direction of the surface veneer.

Another form of mesh which may be used, is one formed from filaments of metal or metal alloy or strands of metal and an appropriate nonmetallic material, e.g. Nylon. Such mesh may be used as a heating means, the mesh being connected to an electrical supply, or may be provided in a surface coating which might be subjected to localised heat, to conduct the heat away from the area and to distribute it over a wider area thereby to decrease the overall temperature and reduce the risk of combustion. In one example the mesh is woven or knitted from stainless steel wire.

The size and nature of the fibres, mesh and sizing are chosen so as to be compatible physically and chemically with the paste. In particular, the mesh. is such that paste including aggregate can flow freely through the interstices of the mesh, the interstices being of a size between one and four times the maximum aggregate size.

Where a surface is covered by a number of pieces of mesh, they should be overlapped at their edges. In an assembly of plywood panels, the mesh is arranged to extend over the butt joints between adjacent panels.

In both methods the paste, which should have adequate adhesion to both the plywood and the mesh, is applied at a coat weight of the order of between 1.5 and 3.5 kg. per sq. metre so that the depth of the layer is greater than the thickness of the mesh.

In one method the mesh is then pressed into that layer of paste so as to be completely embedded therein. This may be done by means of a roller comprising a handle having a cylindrical roller body, for example of sponge, rotatably mounted thereon.

As a result of the predetermined relationship between the sizes of the interstices of the mesh and the particles of the aggregate, paste including aggregate flows from behind the mesh, through the interstices to form a layer of paste covering the mesh. The mesh is therefore completely enclosed within a homogeneous layer of paste applied to the plywood, the layer having a continuous, uninterrupted outer surface.

The coating may be decorated by painting but this is unecessary since the coating can be coloured by including pigments in the paste and in addition the surface of the coating can be patterned by means of the roller simultaneously with pressing of the mesh into the layer.

In summary, a preferred embodiment of the first method comprises:- 1. the application to a surface by a roller of an emulsion bound, extended, pigmented and aggregate-containing coating to a suitable depth, and 2. the immediate application to the coating of a mesh which is such that all the components of the coating including aggregate can pass through it when the mesh is pressed into the coating by a roller, so that the mesh becomes completely embedded in the coating, the coating being textured simultaneously with pressing of the mesh into it.

In the second method the mesh is also pressed into the layer of paste by means of a roller but this may be done only to an extent such that at least some parts of the mesh are left exposed. As in the first method paste including aggregate flows from behind the mesh into its interstices so that the mesh is embedded in a homogeneous mass of paste.

When the layer of paste has partially or completely set, a second layer of paste is applied to it to obliterate the mesh. The paste is similar to the paste used for the first coating and is also applied by means of a roller. The operative surface of the roller may be patterned to produce a decorative finish on the surface of the second coating in the same way as such a finish may be provided on the one coating of the first method.

The surface may be painted but this is unecessary if the paste used for the second layer is pigmented.

In both methods, if the paste does not fill any gaps, e.g. knotholes, in the plywood surface to be coated, it is necessary to use a suitable filling compound to fill-such gaps, the filling being flush with the face veneer of the plywood so that there are no voids behind the overmeshing system.

One advantage of the invention is that the tools required are very simple and inexpensive, and in the case of the first method only one wet application is necessary, although in both methods prior priming/sealing may be necessary.

Another advantage of the invention is that it facilitates the coating of a large surface area easily and quickly, the use of a roller having the particular advantage that unlike, say, a blade, it does not pull the mesh and rumple it. The methods may be used either in a factory or on site, a monolithic appearance can be produced even with many butt-jointed boards in the substrate, and in the case of boards to be coated after assembly the boards may be cut to size before coating with no ill effect on the coating. All fixings may be covered by the coating. Wet coat weights may be accurately determined and controlled, and the resulting finish can have the appearance of a standard textured coating, i.e.

there is no evidence of the presence of the mesh.

The mesh provides mechanical strengthening and does not appreciably alter the moisture permeability of the decorating system. Thus, the coating does not seal in (or out) moisture, and hence has a minimal effect upon the balanced construction of the plywood, thereby minimising macroscopic defects such as "bowing" and durability problems associated with accidental damage to the surface allowing the ingress of moisture which might be trapped.

Claims

1. A method of coating a surface of a building or of a building component which involves the use of a continuous sheet material formed with interstices of a predetermined size and a settable paste comprising liquid binder and aggregate of a predetermined size or sizes smaller than the interstices of the sheet material, the method comprising the steps of applying the paste to the surface to form a layer of a depth greater than the thickness of the sheet material, placing the sheet material against the external surface of the layer and pressing it into the layer whereby, as a result of the predetermined relationship between the sizes of the interstices and the aggregate, paste including aggregate flows into the interstices of the material so that the coating thus formed comprises a homogeneous mass of paste extending behind and into the interstices of the sheet material which is thereby embedded in it, and then allowing the paste to set.

2. A method as claimed in Claim 1 wherein a second coating is applied to the coating.

3. A method as claimed in Claim 2 wherein the second coating is applied immediately after pressing of the sheet material into the layer of paste.

4. A method as claimed in Claim 2 wherein the second coating is applied after the first coating has partially set so that a skin has formed on its exposed surface.

5. A method as claimed in Claim 2 wherein the second coating is applied after the first coating has completely set.

6. A method as claimed in Claim 2, 3, 4 or 5 wherein the second coating is formed from a settable paste comprising a liquid binder and aggregate.

7. A method as claimed in Claim 6 wherein the aggregate of the paste used for the second coating is of the same size or sizes as the aggregate in the paste used for the first coating.

8. A method as claimed Claim 6 or 7 wherein the paste used for the second coating is pigmented to provide colour and durability.

9. A method as claimed in any one of Claims 2 to 8 wherein as the second coating is applied, its outer surface is formed into a decorative finish, for example a stippled finish.

10. A method as claimed in Claim 1 wherein the sheet material is pressed completely beneath the surface of the coating so that paste including aggregate flows through the interstices in the material to form a layer of a homogeneous mass of paste covering the material whereby the coating has a continuous outer surface.

11. A method of coating a surface of a building or of a building component which involves the use of a continuous sheet material formed with interstices and a settable paste comprising aggregate and liquid binder, the method comprising the steps of applying the paste to the surface to form a layer of a depth such that the sheet material can be completely embedded therein, placing the sheet material against the external surface of the layer and pressing it beneath the surface of the layer, the paste and the sheet material being such that on pressing of the material into the layer of paste, paste including aggregate flows through the interstices of the material whereby the coating thus formed comprises a homogeneous mass of paste having a continuous outer surface and with the sheet material embedded in it, and then allowing the paste to set.

12. A method as claimed in Claim 10 or 11 which includes, after pressing of the sheet material into the layer of paste and prior to setting of the coating, forming the outer surface of the layer into a decorative finish, for example a stippled finish.

13. A method as claimed in Claim 10, 11 or 12 wherein the paste is pigmented to provide colour and durability.

14. A method as claimed in any one of the preceding claims wherein the paste contains no more than 30% by volume of aggregate.

1 5. A method as claimed in any one of the preceding claims wherein the aggregate consists of particles which are no more that 2 mm. in size.

16. A method as claimed in any one of the preceding claims wherein the aggregate contains particles of different sizes.

17. A method as claimed in any one of the preceding claims wherein the liquid binder is in the form of a solution, for example water-carried.

18. A method as claimed in any one of Claims 1 to 1 6 wherein the liquid binder is in the form of a suspension.

19. A method as claimed in any one of the preceding claims wherein the paste has a nonvolatile content of between 30% and 86% by weight.

20. A method as claimed in any one of the preceding claims wherein the coat weight of the paste is between 1 and 5 kg. per sq. metre.

21. A method as claimed in any one of the preceding claims wherein the interstices of the sheet material are of a size between one and four times the maximum aggregate size.

22. A method as claimed in any one of the preceding claims wherein the sheet material is a woven or non-woven mesh.

23. A method as claimed in any one of the preceding claims wherein the sheet material is pressed into the layer of paste by means of a roller.

24. A method as claimed in Claim 23 wherein the roller is formed to provide the surface of the coating with a decorative finish.

25. A method as claimed in any one of the preceding claims wherein the paste is pigmented.