All building cleaning projects require an understanding of the masonry, the type of soiling and the relationship between the two. Where brickwork and terracotta are concerned, the effect of weathering on both the units and their joints is a fundamental part of this understanding, While both materials are fired clay, they both have unique properties and sensitivities as regards cleaning.

When selecting an appropriate brick cleaning method the starting point is understanding the material

The term brickwork describes fired clay units, which we know as bricks and terracotta. Bricks have a bewildering variation of constituents and properties. While bricks are made mainly from clay earth and fired in kilns, the variety of clay types, moulding and firing processes means a huge difference in the bricks properties, affecting not just surface texture and colours, but also the way they respond to brick cleaning.Bricks in heritage walls vary from soft hand made bricks to highly fired engineering bricks and vitrified blue bricks, roughly textured stock bricks to shiny glazed brick.

Even within a single brick, variations in surface texture and hardness will be found which may prevent the safe use of abrasive cleaning, or reduce the pressure at which water jets cleaning can be used safely. Porosity also varies, and high absorbency may eliminate chemical cleaning regime or processes involving large volumes of water.

Abrasive cleaning is frequently damaging and generally best avoided. Abrasive brick cleaning systems are usually inappropriate on historic brickwork due to the nature and characteristics of the brickwork, even when undertaken extremely carefully. This is because these methods are unable to deal with the multitude of variations that can be present in a brick wall. Abrasive brick cleaning is particularly inappropriate for the removal of paint or graffiti on brickwork

Most brick types are also susceptible to impact damage and readily damaged by abrasive cleaning. Some have a fine surface layer of densely packed particles created from the firing, This is known as a “fire skin” this must never be affected by cleaning processes as any change in the integrity of this delicate layer will rapidly increase the rate of decay of the brick

Periods of saturation associated with water washing, chemical cleaning or wet abrasive cleaning can lead to the emergence of efflorescence. These salts within the brick masonry and lime mortars are dissolved by wet brick cleaning and leach through to the surface as the brick dries.

Any brick cleaning method involving water alone will only remove loosely adherent dirt, unless excessively high pressures are used, as water cannot break the siliceous bond by which soiling adheres to the brick.

Heritage stonecare gives careful consideration to the effect of the cleaning methods used on the mortar, as traditional brick pointing mortars based on soft mixes of lime and sand, are usually much softer and much more absorbent than the surrounding brick. Pre-wetting and rinse water pressures are kept low to avoid and damage to the mortar during the cleaning process. Chemical cleaning is generally the most suitable approach as it is able to accommodate variations in texture, condition and hardness, and it is undoubtedly the safest brick cleaning method for the removal of paint. For tough dirt, cleaning can involve an alkali-based degreaser followed by hydrofluoric get, The brick surfaces to be cleaned are thoroughly pre-wetted to limit the activity of cleaning agents to the surface only. Thorough rinsing cleaning agents after work is complete is critical to a professional and sensitive restoration.

At Heritage Stonecare we believe the successful cleaning of external brickwork and terracotta depends on well-trained and experienced operatives. A specification, no matter how good it is, will remain words on paper unless good workmanship is available to translate it into good practice.

A key factor in successful cleaning is the skill and experience of the specialist contractor. The starting point is understanding the material

·       heavy soiling on some brick surfaces (for example, London stocks and Norfolk whites) is resistant to hydrofluoric acid-based chemical cleaners

·       glazed bricks are sensitive to etching by hydrofluoric acid-based cleaners and damage by abrasive cleaning processes

·       Victorian patterned brickwork may contain bricks of several colours and degrees of hardness. These will have different sensitivities to both chemical and abrasive cleaning processes

·       heavy soiling on some brick surfaces (for example, London stocks and Norfolk whites) is resistant to hydrofluoric glazed bricks are sensitive to etching by hydrofluoric acid-based cleaners and abrasive cleaning