Maintenance of facades

Preparation before cleaning
Cleaning must be preceded by preparation that consists of setting up scaffolding, confirming the diagnostic, removing planters and flower pots, disassembling some equipment (blinds, shutters, etc.), putting up the necessary protection, checking the condition of joints (it is strongly recommended that joints around window frames should be caulked with an elastomer mastic).

Cleaning with water
Cleaning with water is done mainly with running water, low pressure cleaning, atomization or nebulization and high pressure cleaning.

Running water using spray manifolds with manual brushing is very often efficient. However, there is a risk of infiltration of water inside the walls and dissolution of joints.

Running water and washing at low pressure does not usually damage stone and is very suitable for weak stone that has to be kept, for example for historic interest. Good elimination of water soluble salts is obtained by these two non-aggressive methods.
High pressure cleaning is a process that uses a cleaner capable of adjusting the water jet pressure (from 5 to 20 MPa) and the flow (set of nozzles).
This method can be proposed for hard and sound stone. Cleaning times are shorter with this technique, sometimes to the detriment of elimination of salts.

Micro sanding
Micro sanding consists of spraying fine glass, alumina powder (from 20 to 200 µm). The jet pressure is adjustable, so that cleaning is perfectly controllable.

Application of chemical products.
Most products available on the market are alkaline. They can give good results, but can also be very dangerous. They are very difficult to use and require rigorous monitoring of usage instructions, particularly strict respect of application times, rinsing and neutralization with control of the pH of treated surfaces. Prior tests are essential to make sure that no secondary undesirable reactions will occur in the medium term. Chemical cleaning can strongly accelerate the deterioration mechanism of fragile stones.

Mechanical cleaning or recutting processes.
This refers to resurfacing processes by grinding or refinishing with a nail float. A certain thickness of the stone surface is removed. On stones that are slightly deteriorated, elimination of a few millimeters is sufficient, but if flaking has occurred, a much deeper recut will be necessary since the surface crust of sulfo-incrustation usually conceals a material severely weathered over a thickness of several centimeters. This recutting should only be done on severely degraded or painted facades. Repairs of moldings and relief should be done independently (laser, recutting by sculptor).

Cleaning of old paint and surfaces
Cleaning of old paint and surfaces should be approached with a great deal of care considering the wide variety of materials. It is usually done using alkaline shampoos. In some cases, it may be necessary or essential to strip the paint to expose the stone (particularly for silicate paint). Mechanical processes (recutting, wet sand blasting) or chemical processes (difficult and long) may be used.

Facade repairs
After facade cleaning operations, deteriorated stone and degraded joints are repaired. There are three possible solutions:
- Replacement of stone by overlay or using the "alternate drawer technique".
- Replacement of stone by a resurfacing mortar that resembles the original appearance and must be compatible with the facade fittings. This second solution is not as durable. Moreover, the mortar usually ages differently from stone and will look different from the rest of the facade in time.
- A chemical consolidation could also be considered (consolidating, mineralizing agents) for weak stone for which the skin is to be kept.