Case 1

Navigation

Introduction

Brown “Coffee” Stains on Panel

Type of Building: Commercial Building

Natural stones used as facade of a tall building are normally granite, or slate. In this case, it is a granite cladding which has experienced brownish staining, a typical kinds of staining arising from the pxidation of the iron minerals of the material itself.

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.

Staining of stone cladding affects the appearance of a building but not the stability of the structure. Staining usually manifests itself as a change in colour of the stone surface from the desired appearance and may be localized patchy in nature or uniform across the stone. Staining occurs in all types of stone including sandstone, granite, limestone and marble.

Staining of panel surfaces is found to be the major defect of stone cladding. Defects could either be built in during the design stage, caused by poor workmanship or due to the lack of maintenance.