Cleaning Stone and Concrete Facades

Cleaning a stone or concrete facade means removing atmospheric, biological and salt deposits without damaging the surface of the material. Proper cleaning not only restores the colour but also extends the life of the cladding: dirt and deposits retain moisture and accelerate deterioration.

The main criterion for choosing a method is the combination of contamination type and material. The same acid wash that is safe for granite dissolves marble, limestone and travertine. That is why any method is first tested on a trial area.

The article is written for property managers, building owners and maintenance contractors. More articles: Facade maintenance, standards and repair.

Facade contamination varies in nature, and each type needs its own removal method.

Contamination is often combined: soot binds with salts to form a dense crust that water cannot wash off.

Cleaning methods from the gentlest to the more aggressive:

• Low-pressure water and brushes — dust, fresh dirt; safe for all materials.

• Pressure washing — effective, but pressure and distance are matched to the material: on soft stones and decoration a strong jet washes out the binder and leaves grooves.

• Steam and hot water — greasy and biological dirt, sealant residue and chewing gum.

• Chemical cleaning — specialist products with dwell time and subsequent rinsing.

• Soft abrasive cleaning (low-pressure micro-abrasive) — dense crusts on strong materials; it removes part of the surface, so it is not used on polished stone or fine relief.

• Poultices — pastes that draw salts and stains out of the pores; slow but gentle, used in restoration.

• Laser cleaning — spot cleaning of valuable decoration.

Harsh sandblasting of stone and concrete is undesirable: the surface becomes rough, the pores open, and the facade gets dirty again faster than before cleaning.

Chemicals are chosen by the type of contamination and the sensitivity of the material.

• Acidic products — efflorescence, cement laitance, rust. Can be used on granite, basalt, porcelain stoneware and sandstone with quartz cement. Prohibited on carbonate stones — marble, limestone, travertine, dolomite, shell limestone (coquina), onyx — which dissolve in acid. On concrete and GFRC, only mild special products with prompt neutralisation, otherwise the cement matrix is destroyed.

• Alkaline products — soot, grease, organic matter, paint residue. Suitable for most materials but require thorough rinsing.

• Neutral detergents — routine washing, sensitive materials.

• Biocides — moss, algae, lichen; after treatment and dwell time the growth is washed off.

• Graffiti removers — gel products matched to the type of paint.

Procedure: trial area, wetting the surface before application (so the product does not soak in deeply), dwell time as instructed, thorough rinsing. Surrounding surfaces, windows and metal are protected with film.

Limitations of cleaning:

• Temperature. Wet methods only at stable above-zero temperatures so that the water can evaporate before frost. Washing in winter risks frost damage.

• Surface condition. Cracks, delamination and weak joints are repaired or protected first: water under pressure gets behind the cladding and into the insulation.

• Rainscreen facades. The jet must not drive water into the joints and the ventilated cavity; insulation that gets wet during washing loses its thermal performance.

• Polished stone — abrasives and acids remove the polish.

• Listed buildings — methods are agreed with restorers and heritage protection authorities.

• Environment and safety — collecting run-off, protecting plants, fencing off the work zone below the facade.

It is worth assessing separately whether cleaning is needed at all. The natural patina on stone often does no harm to the material and is perceived as part of the building's character, while aggressive cleaning for a "like new" look can remove more than dirt. On valuable facades the aim is to remove what destroys the material (salts, crusts, biological growth), not to achieve a uniform colour at any cost.

For rainscreen systems it makes sense to combine cleaning with a scheduled inspection: joints, fixings and the condition of the cladding are checked from the same gondola or platform, reducing the overall cost of access.

After cleaning, the surface is more open than before and takes up moisture faster. That is why cleaning is usually finished with protection:

• Water-repellent treatment — silane-siloxane impregnations reduce water absorption, efflorescence and deposits while keeping vapour permeability.

• Anti-graffiti coatings on lower tiers: sacrificial (washed off together with the paint and reapplied) or permanent.

• Joint repair and sealing of junctions.

• Removing the causes — fixing sills, downpipes and leaks that caused the deposits.

The impregnation is applied to a dry surface after allowing it to dry following washing. For stone, choose products that do not change the colour, or check the "wet stone" effect on a trial area.

TECHNOFORMA Group supplies natural stone — granite, marble, limestone, travertine, sandstone, dolomite, shell limestone and other stones — and clads facades in stone, GFRC and porcelain stoneware. An example of a facade with stone and concrete:

• Dinastia club house in Kislovodsk — 700 m² of granite, 6,000 m² of GFRC and 700 m² of porcelain stoneware; design and installation.

On such facades the combination of materials calls for a separate cleaning approach for each: granite tolerates more active products than concrete elements, and adjacent surfaces are protected from each other during treatment. The company supplies stone from its warehouse in the Moscow Region and to order, so when a damaged slab is replaced, material from the same quarry and with the same finish is selected.

All projects are under TECHNOFORMA projects. If cleaning is part of work on a historic building, continue with Restoring a historic facade: decoration and stone.