|1.||Rendered coating element in particular coating elements for buildings, characterized in that it comprises a rendered metal sheet with an alumi¬ nium containing surface on which there is an alkalic plaster. Coating element according to claim 1 , characterized in that the plaster contains an alkalic organic binding agent. Coating element according to claim 2, characterized in that the binding agent is an acrylic dispersion. Coating element according to claim 3, characterized in that the acrylic dispersion comprises acrylonitrile. Coating element according to anyone of the preceding claims, characterized in that the metal sheet is a steel sheet with an aluminium containing coating. Coating element according to claim 5, characterized in that the aluminium containing coating comprises a hot dip applied zincaluminium alloy. Coating element according to claim 6, characterized in that the zincaluminium alloy contains at least 50 weight % aluminium. A method to render a steel sheet, characterized in that an aluminium containing coating is first applied to the steel sheet and an alkalic plaster is then applied. A method according to claim 8, characterized in that the sheet is hotdip galvanized with a zincalumi¬ nium alloy. A method according to claim 8 or 9, characterized in that a plaster is applied that comprises an acrylic dis¬ persion, preferably acrylonitrile, as a binding agent.|
This invention relates to a rendered coating element for buildings and to a method to render a steel sheet.
Sheet steel has become a common material for facades both when insulation is added to older buildings and when facade cassettes are made. Facade elements with painted sheet steel are used mostly for industrial buildings since more conventional facades are usu¬ ally wanted for houses and apartment buildings. Rendered sheet steel is normally not used since the adherence of the plaster is poor. Painted sheet steel is commonly used for roofing.
It is an object of the invention to provide for a rendered coating element that is light and durable and has an aesthetic appearance.
This object is accomplished by a coating element that comprises a metal sheet with an aluminium containing surface on which there is an alkalic plaster. Preferably, the matrix (the binding agent) of the plaster comprises an acrylic dispersion such as acrylonitrile.
Advantageously, the sheet metal comprises hot-dip galvanized sheet steel galvanized in a bath of aluminium and zinc. Such sheet steel with a metal coating comprising 53 % Al and 44 % Zn and about 1 % Si is available as ALUZINK®. The sheeting need only be washed with a detergent before the plaster is applied. No chemical pretreatment is ne¬ cessary and no primer is necessary. The adherence seems to be further improved as time goes on.
A plaster that bas been tested comprises BONOTEX®503 (acrylonitrile) as matrix and binding agent, crushed marble, and pigment. The crushed stone was in the size internal 1-3 mm and the plaster was sprayed onto ALUZINK® sheet steel. This plaster dries and hardens in the air and emits no solvents but water.
When tested on a steel sheeting that was hot-dip galvanized with zinc without alumi¬ nium, the adherence, and in particular the long term adherence, was inferior to the ad¬ herence to the aluminium containing surface.
Sheet metal with a thin plaster in accordance with the invention, can be used for pre¬ fabricated facade elements, insulated or non-insulated, but it is also possible to mount uncoated ALUZINK® sheet steel and then wash it with a common detergent. The plaster is applied to the sheet steel when the latter has dried. Preferably, the plaster is sprayed onto the sheet steel.
Sheet steel can be formed into a pattern, for example into the pattern of tiles and the plaster can then be applied. The adherence and elasticity of the plaster is such that it can alternatively be applied to the sheeting before the forming.