Case 2

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Maintenance and Diagnostics

Natural Stone is basically a porous material that absorbs spills and stains if left untreated. Cleaning stone with quality impregnating sealer will prevent most stain from damaging the investment. When using stone as the external façade, the recommended sealers are the ones that give the repellency against weathering and ultraviolet rays. Once sealed, the stone will be more protected and hence with proper cleaning, it will retain the sealer longer and keep your stone protected without damaging the stone’s natural beauty.

A silane-based impregnating agent, which penetrates into the pores of the stone while leaving the surface breathable is recommended. As a natural material, the façade stone is porous, and thus susceptible to the effects of increased air pollutants and dirt.

The façade treatment is re-applied approximately every five years. The basic cleaning is done by using high pressure water pump. The façade protection treatment is then applied to the entire façade.

Alternatively, the façade can be cleaned by projecting very fine powders with low pressure compressed air. This process removes unsightly dirt and pollution deposits from interior and exterior surfaces of limestone, sandstone, granite, marble, brick, concrete aggregate stone, slate and stucco. It does not damage even historic building fabric fabric in the short or long term and includes a dust containment system to ensure nuisance-free cleaning.

The fine powder remains in the airflow as it disperses outward along the surface. In moving with the flow, these low mass particles slowly diminish the dirt layer with a rubbing action, unlike the direct, high-force impact of sand in traditional blast methods

Maintenance

Consider availability of adequate water supply, drainage provisions and electrical power supply to choose a façade cleaning method. Records of cleaning operations (including photographs before and after cleaning, and drawings of nature of deposits, thickness and patterns) should be kept for buildings of significance in accordance with BS 8221-1, SS 509-1 or equivalent. Maintain the façade in a state as near as possible to its new condition. Ease of façade maintenance can be expressed by the frequency of necessary maintenance operations, labour and supplies necessary for each maintenance operation,
and number of possible ways of removing stains, graffiti, etc., or ISO 7361 or equivalent.

Detect/determine staining of porous substrates by joint sealants (ISO/NP 16938-1). Adopt the recommendations for treatments for controlling organic growth in accordance with BS 8221-2,
SS509-2 or equivalent. Repair painted surfaces damaged by wear and tear; wash down; remove defective
paint film; apply sealer/primer (if necessary); and repaint in accordance with BS 6150, SS 542 or equivalent. TiO2 only works where there is sunlight. Conventional cleanings are still needed for non-coated areas. For areas coated with TiO2, conduct neutral cleaning annually.

Periodic cleaning is necessary to maintain the aesthetics of tiled façades. A neutral cleaning agent should be adequate if a periodic maintenance schedule is performed.

Diagnostics of Defects (see also NDT)

The range and degree of the staining can be assessed by visual inspection.
Petrography can also be used to analyse staining occurring on stones.
Scanning electron microscopy (SEM): determines the surface characteristics of stones.
Mercury porosimetry to determine the porosity or pore space of the stone to allow water to be present. It is one of the most useful methods to investigate the porous structure of solid samples in a quantitative way. It provides reliable information about pore size/volume distribution, particle size distribution, bulk density and specific surface for most porous solids regardless of their nature and shape.
Thermography is used to determine the presence of water retained in the pores of the granite panel.

Optical camera on a drone