Granite
Defect and Repair
| Granite | Defect | Repair |
 |
Staining May be caused by the natural property of the stone, efflorescence of the precast concrete backing, sealant used and other factors. |
Cleaning by water coupled with scrubbing or high pressure water jet could effectively remove most of the stain from the stone cladding surface. Cleaning should begin at the top so that excess water can run down and pre-softens the dirt below.
Acidic cleaning agents should not be used for granite as it attacks pyrite (iron sulphide) |
 |
Efflorescence | Cleaning by water coupled with scrubbing or high pressure water jet could effectively remove most of the stain from the stone cladding surface. Cleaning should begin at the top so that excess water can run down and pre-softens the dirt below.
In conjunction with water spray or chemical cleaning, fiber or bronze brushes might need to be used. |
 |
Cracking Cracks across the span of the marble strip were found mainly at the corners.
|
To replace the affected panel by a new one and provide sufficient cushion to absorb various stresses created by the deformation of the structural frame, differential thermal movement between the concreter baking and the panel, or the accidental external impact load.
Hairline crack can be filled with epoxy resin, and re-polish the surface. |
  |
Rising dampness Rising damp in the façade material may result in moisture penetrating into the interior of the building, damaging floor finishes |
The simplest method is by torching or heat treatment and after that impregnating agent is applied on the exposed sides of stone.
Installation of a new DPC in an existing wall:
|
 |
Organic growth | Can be removed dry with wooden scrappers and/ or brittle brushes or may be removed using high pressure water lance.
In all cases, the cleaned surface should be treated with a suitable and approved anti-fungidal wash. |
 |
Sealant Staining This is due to the poor workmanship, when the stone is not sealed properly, especially around the edges and after installation of the sealant, the plasticizer in the sealant will migrate into the pores of the stone over a period of time. This results in the bands of dirt on the stone surfaces. |
Scrap out the sealant, clean the affected parts with some chemical solution (e.g. alchohol or thinner) and then reseal the stone and apply sealant to the joints.
The proper selection of sealant is important. Silicon based sealant is recommended e.g. polysulphic sealant |
 |
Surface Unevenness Poor workmanship during the installation of tiles on the backing wall. Thermal expansion of the tiles coupled with insufficient expansion joints allowed between the tiles causes the tiles to push against each other and some to jut outwards. |
Replace the defective panels. The new stone should match the original stone in color, graining, finish, and light reflectance as well as in physical and chemical properties. |
|
Watermark Stone is not sealed properly, causing the water from the ground to raise and enter the pores. |
Use a soft bristle brush to clean into the crevices of the stone. Rinse the stone well and allow to dry. If any stains remain, try a stone poultice on them. The poultice may need to be reapplied two or three times on stubborn stains.
Unfortunately, the scratches can’t be removed without severely altering the surface of the stone. Once the stone has completely dried apply a color enhancing penetrating stone sealer and the scratches will be unnoticeable |
Note: For more defects, please refer to the Defect Library.
The method of repair should comply with CP 67 Part 1:1997 Code of practice for cleaning and surface repair of buildings – Natural stone, cast stone and clay brick masonry.