GB2233685A - Keying plaster to e.g. a lintel - Google Patents

Abstract

A lintel (10) having a plaster keying surface is formed by the outer surface of a textured coating (12) applied to a flange (16) of article (10). The textured coating (12) is formed by discrete material e.g. sharp aggregate (20) being bonded to the flange (16). The discrete material (20), being of mineral or plastics material, is bonded directly to the flange (16). The bond to the flange (16) is by an adhesive (22) or by the use of a resin surface coating which is polymerizable after discrete material (20) has been placed thereon. <IMAGE>

Description

ARTICLE HAVING A PLASTER KEYING SURFACE.

This invention relates to an article having a keying surface for rendering such as plaster, the article being particularly, but not exclusively, a metal lintel which has been fabricated from, for example, zinc coated or galvanised steel sheet.

Steel lintels are well known and are manufactured mainly from galvanized mild steel sheet but in use, in the construction industry, there is the problem of integrating zinc coated steel into what is basically a mineral matrix, namely bricks, concrete blocks and cement, grout or plaster all of which are water absorbent in contrast to the water repellancy of the zinc coated steel.

Heretofore, the surface(s) of a steel lintel which requires rendering with, for example, gypsum plaster or Portland cement mortar has each been clad with a keying surface in the form of expanded metal or the keying surface has been formed by the surface of the lintel being interfered with by being, for example deformed or perforated.

Examples of this keying technology are to be found in numerous published British patent specifications on the subject and the following are representative of mesh, strip perforation and strip deformation, namely GB 2,136,846; GB 2,134,560 and GB 1,514,471.

It is apparent from the prior art' that the method of providing a plaster keying surface for rendering a metal surface, such as surface of a lintel, is to attach mesh, or interfere with the surface concerned by, for example perforating or deforming it. This method involves an extra manufacturing step or steps and therefore increased labour costs, but in the end the rendering is held in place by the dovetailing action only of the rendering passing through the apertures in the surface and hardening therethrough since all the metal surfaces are completely water repellant or nonabsorbent. Such plaster keying surfaces are therefore disadvantages.

It is an object of the present invention to provide an article with a plaster keying surface which obviates or mitigates the above disadvantage.

Accordingly, a first aspect of the present invention is an article having a plaster keying surface formed by the outer surface of a textured coating applied to the article or part thereof.

Preferably, the textured coating is formed by discrete material being bonded to the article or part thereof. The discrete material is desirably bonded directly to the article or part thereof. Alternatively, the discrete material may be bonded indirectly by being provided on a skin or backing sheet bonded to the article or part thereof. The discrete-material is p preferably of mineral or plastics material.

Preferably also, the bond to the article or part thereof is by an adhesive or by the use of a resin surface coating which is polymerizable after discrete material has been placed thereon.

Accordingly also, a second aspect of the present invention is a method of providing a plaster keying surface on an article comprising the step of applying a textured coating to the article or part thereof.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, which shows an end elevation of a lintel having a plaster keying surface.

Referring to the drawing, an article ie. a metal lintel 10 has a plaster keying surface formed by the outer surface of a textured coating 12 applied to the article or part thereof. The lintel 10 is of general inverted channel shape with a flange 14, 16 extending outwardly from the outer ends of the limbs of the inverted channel shape. The channel is filled with a self-skinning polyurethane foam filling 18. The flange 16 has the textured coating 12 applied to its surface as shown.

The textured surface is formed by discrete material 20 being bonded directly to the flange 16. The discrete material is of mineral or plastics material.

The mineral discrete material is selected graded crushed stone, or gravel which is set as a tenacious screed on the flange 16 by the use of the adhesive or polymerizable resin coating.

The bond to the flange 16 is by an adhesive 22 or by the use of a resin surface coating which is polymerizable after discrete material 20 has been placed r thereon.

Whilst the polyurethane foam filling 18 does not form part of this invention, it is the subject of our co-pending application No. 8908472.7 entitled "Steel Lintels" and it is pertinent to note that in practice it is common for the resin, or adhesive, to flow around the channel bend of the lintel 10 and adhere to the skin of the foam 18 as is indicated at 24; consequently often the coating 12 extends as far as this point.

Development work has revealed that almost any type of mineral aggregate can be used in this application.

For example, good adhesion and keying results have been obtained with the use of limestone, crushed brick, basalt, granite, sandstone and the like and a range of adhesives and resins have been found to be satisfactory.

As regards the use of adhesives and resins, there are two distinct modes of employment. The first is the use of adhesives in the form of emulsion polymers and spreadable mastics, and the latter can be based on either aqueous emulsions of polymers or solvent solutions of polymers. Both are satisfactory but differ greatly in drying times at ambient temperatures. The second is the employment of polymerizable resin components, in the form of twin packs, which consist of a resin base and a catalyst or polymerization accelerator.

Examples of suitable aqueous systems are plasticized vinyl and acrylic emulsions whereas suitable low boiling point solvent systems are based on petroleum/ester solutions of rubbers with resins such as colophony or coumarone-indene.

Aqueous systems require the application of hot air blasts in order to give fast enough drying to suit industrial production speeds and the organic solvent systems require strict control in terms of flammability and health and safety ventillation procedures.

The preferred method is to operate at or near ambient temperatures with the use of catalyzed polymerizable resin systems and the most successful to date are those based on epoxy resins (Araldite-Trade Mark) both the normal and fast (5 minute) grades; acrylics (peroxide polymerised); polyesters and any of these used filled with mineral powders or made thixotropic with fumed silica.

It is apparent that the resin surfaces, as used in this invention, will be just as non-absorbent, or water repellent, as the galvanized steel sheet itself so it is important that the textured coating has the mineral aggregate exposed, or protruding, in the uncoated state from the resin or adhesive bed. More than 60% of the mineral surface can be made to receive aqueous cement or plaster coats if the nominal size of the sharp aggregate used is at least twice the applied thickness of the p resin or adhesive film.

It has also been found that the best keying results are obtained if the aggregate selected is one which has good water absorption values, for example 0.38 to 2.0% for limestones and 2% to 5% for crushed clay engineering bricks.

There is always a variation in the quality, if not the thickness, of zinc coatings on steel and in certain circumstances it has been found to be beneficial to pretreat the surface of the lintels with a metal etch primer or to obtain the same result by the use of an acid or alkaline (metasilicate) wash. This is important when the zinc surface is highly crystalline and feathered.

It will be apparent to those skilled in the art that there are different ways of applying this invention to impervious surfaces which need to be rendered with plaster or cement. To illustrate this point, it can be stated that good results have been obtained in an automated process where a polyolefin hot melt adhesive p was applied to a moving belt system of lintels, placed end to end, with the adhesive applied by means of a lick-roller and the aggregate shaken on by the use of an overhead vibratory, reciprocatory or oscilliatory screen.

The article to which a plaster keying surface is to be applied can be any impervious surface and noc necessarily of metal, for example of plastics material, care of course being taken on what adhesive or resin is used for the bonding.

In a first modification, the discrete material may be bonded indirectly by being provided on a skin or backing sheet then bonded to the article or a part thereof.

Variations and other modifications can be made without departing from the scope of this invention above described.

Claims (9)

CLAIMS:

1. An article having a plaster keying surface formed by the outer surface of a textured coating applied to the article or part thereof.

2. A method of providing a plaster keying surface on p an article comprising the step of applying a textured coating to the article or part thereof.

3. An article as claimed in Claim 1 or 2, wherein the textured coating is formed by discrete material being bonded to the article or part thereof.

4. An article as claimed in Claim 3, wherein the discrete material is bonded directly to the article or part thereof.

5. An article as claimed in Claim 3, wherein the discrete material is bonded indirectly by being provided on a skin or backing sheet then bonded to the article or part thereof.

6. An article as claimed in Claim 3, wherein the discrete material is of mineral or plastics material.

7. An article as claimed in Claim 3, 4, 5 or 6, wherein the bond to the article or part thereof is by an adhesive or by the use of a resin surface coating which is polymerizable after discrete material has been placed thereon.

8. An article having a plaster keying surface substantially as hereinbefore described with preference to the accompanying drawing.

9. A method of providing a plaster keying surface to an article or part thereof substantially as hereinbefore described with reference to the accompanying drawing.