The unplastered look of brick, stone, concrete etc. is robust and rustic. This rustic and robust look sometimes gives an impression that it is permanent. A new unplastered surface may be bright and appealing yet in course of time weathering makes it look patch-work of colours due to efflorescence salts soot, dust and rain.
In the case of concrete, the differences in colour of each batch of cement, the aggregates textural changes on account of form work mould oil, etc., makes the position worse. Thus, maintenance of buildings with such surfaces is required from time to time to maintain the looks.
Brick Work
Exposed architectural brick work requires cleaning every year by water and stiff non-iron brush. Detergents are not called for except in small very difficult and dirty patches. Efflorescence, here, is removed by brushing before the wash. Washing the area before removing salts has the effect of dissolving the salts which may get driven inside or form salt solution and rundown. Therefore on drying efflorescence reappears. For water repellancy in exposed work colourless repellants like silicone could be used. Mortar joints may require repointing from time to time.
Stone Work
Water cleaning: For the maintenance of buildings where stone is used, periodic cleaning at least once a year is carried out by hosing the building by copious amount of water and then brushing it down with a stiff non-iron brush. The water jet spray should have very high pressure of 32 kg/cm^2. However, in case of lime stone the best way is to imitate action of rain. Water should be free from iron salts. Non-corroded containers should be used. It is not necessary to add detergents.
Steam cleaning: Steam is applied from a jet. Calcium sulphate deposits get reasonably quickly removed.
Sand blasting: Granites and other hard varieties of stones can he effectively cleaned by sand blasting. (Lime stones will get damaged by sand blast). For delicate work, copper shot blasting is preferable. Granites and such other harder varieties could be rechiselled to give fresh look. In the maintenance of buildings where the depth of decay is great either the entire stone is cut out and replaced or stone veneer is put up. The replacement stone should be of similar nature and texture. It may be preferable to remove an old stone from inconspicuous place in the building so that matching is good and the patch is at inconspicuous place. Very minor patches could be done by artificial stone plaster. How so ever correctly these patches are done, they are not as good as stone.
Exposed Concrete
For the maintenance of buildings where there is exposed concrete on the surface, one of the ways of preserving look of exposed concrete would be to, give a clear water repellant coatings like silicon, etc. When the concrete is set hard, the look is fresh. However, these coatings have a short life of two-three years and are required to be redone like paints. Such clear coatings would be needed specifically in the following circumstances:
- When the building is situated in a polluted area.
- Pedestrian area.
- Where white cement is utilised.
Methods used for cleaning stone work are also valid for concrete. Sand blasting can also be used.
- Stains – All exposed masonry would get stained due to accidents, traffic, vandalism, etc. Stains removal from surfaces is needed from time to time. Treatment for common type of stains is as
- Iron Stains: For Large areas, affected solution of 1 kg of oxalic acid to 1 litres of water may be prepared and spread on the surface and left for three hours. Then surface should be scrubbed with dilute detergent solution and finally rinsed thoroughly with water. For very hard stains, the solution of sodium citrate (about 3 oz to a pint of water and pint of glycerine) could be used.
- Ink Stains: Ink stains can be normally removed by hydrogen peroxide or a solution of sodium perborate.
- Lub Oil: Oil stains can be removed by poultice treatment of 1.5 oz of tri-sodium phosphate to a pint of water making a paste with whiting or powdered chalk.
- Paints: Paints can be removed by solvent type paint strippers.
- Fire Stains: The stains caused by the smoke of the fire are very persistent and are difficult to remove. Stains penetrate very deep.
