Case 5
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Cause of Defects
Staining of stones may be caused by the natural property of the stone. The natural property of stone to absorb water rapidly coupled with its high porosity, causes stone to discolour quickly. Areas where frequent washing by rainwater occurs will darken considerably as compared to areas that are sheltered.
Water being absorbed readily by the granite is not able to evaporate fast enough thus allowing the pores of granite to be saturated with dampness all the time.
Dampness allows atmospheric dust to adhere better as compared to dryer areas. In the process, dirt may also penetrate into the pores of the stone.
Water causes uneven dirtying when it flows over the ledge, washing dirt or dissolved substances from the horizontal ledge and depositing them on others.
The figure shows a test done in the laboratory, to show the extent of darkening of a stone sample upon contact with water.
Staining on a facade has a lot to do with the pattern of rainwater runoff, which in turn is dependent on the facade configuration, colour, texture, as well as the “roughness” and “water absorption” properties of the materials used:
See also Staining of Facades