Case 5

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Introduction

Runoff from Ledge

Type of Building: Commercial Building

This case shows staining on the granite façade. Stains marks streaks from the top ledge. The stain marks may become unremovable if left uncleaned for a long time, and there could be a loss in the aesthetics of the façade if discoloration is widespread.

Granite is an igneous rock. It is formed as a result of the slow crystallisation of molten magma at depth in the earth’s crust. Uplift and erosion has over millions of years, resulted in this material outcropping at the surface. The minerals which make up granite are generally quartz, felspars and various mafic minerals (amphiboles, pyroxenes, micas and secondary materials). It is the size, distribution and precise chemistry of these minerals which give the granite it’s colour. The silica content of a granite should be at least 70%. In the stone industry “granite” has been a term applied to almost all igneous rocks and schists. Traditionally, granite refers to any very hard crystalline rock (quartz based as opposed to marble), calcite based possessing the following characteristics:

With no apparent natural jointing, being difficult to work without special tools,
That takes a high polish and,
Is extremely resistant to natural weathering.

Granite can be worked to achieve every type of finish; from traditional hand tooled, flame textured, shot blasted, acid washed, or honed to highly polished mirror finishes.