Methods & considerations for water cleaning clay brickwork

Clean brickwork following a build is desirable to ensure client satisfaction, but what water cleaning methods should be used to achieve this?

There are many reasons why brickwork becomes soiled during the construction process, whether it be from mortar residue and splashes or staining from other sources. However, before we consider what cleaning methods are available, one approach should be ruled out immediately: HIGH PRESSURE WATER WASHERS!

The problems with high pressure water washers

Brickwork is designed to perform adequately under normal weathering cycles, including wind driven rain, as long as it is constructed in accordance with the recommendations set out in British and European Codes of Practice.

The introduction of high-pressure water abrasion during cleaning processes can blast away mortar and damage the texture of bricks leaving the surface of the building vulnerable to future water penetration from wind driven rain and potentially frost attack. The damage that can be done in the wrong hands can lead to serious repercussions for the appearance and long term durability of the brickwork.

Methods of water washing

When using water to clean the exterior brickwork it is important to protect the surrounding surfaces as large amounts of water are potentially damaging. Proper precautions and supervision should be provided to safeguard that water does not enter core material. A system should be established to ensure the following:

• the minimum practicable amount of cleaning water is used with low pressure application

• all potential water entry points should be thoroughly sealed

• temporary catchments and gutters are provided, if required, to efficiently remove water from the surrounding area and to avoid over-saturation at lower levels

Differences in surface texture, porosity, colour and hardness of clay bricks, within a wall (or even within individual bricks) should be identified prior to carrying out any cleaning operation. Hardness and condition of mortar joints should also be assessed.

All the following cleaning methods should be undertaken by specialists.

Low pressure water washing

Low pressure water based cleaning methods can be used to remove loosely adherent deposits with light brushing using a soft brush, if required. A proprietary brick cleaning agent should be used to remove mature deposits followed by a low pressure rinse with clean water. Please note: with established brickwork- the main problem is atmospheric soiling, which is generally not water-soluble.

Nebulous cold water spray

Sheeting protection should be used to prevent fine spray drift. Water penetration and associated damage can occur.

Low pressure washing (Up to 250 psi (17 bar))

Low pressure washing should be used in the following ways during brickwork cleaning:

• after softening the deposit with fine water spraying
• to rinse off superficial deposits (e.g. organic growth) from masonry prior to carrying out another cleaning process
• rinsing off wet abrasion debris
• pre-wetting and rinsing surfaces for chemical cleaning

CAUTION: Low pressure washing can damage friable stone, soft stone, and weathered or sound sand lime mortar joints. Water penetration and staining problems can also occur due to the large quantities of water used with this technique.

Cleaning Method Low Pressure psi (bar) Medium to high Pressure psi (bar)
Water washing Up to 250 (17) 250 to 1000 (17 to 69)

PLEASE NOTE The operating pressures given are not necessarily the pressures at the wall face. The following factors may also be strongly influential:

• water flow rates
• nozzle shape and size
• nozzle wear
• distance between the nozzle and the wall
• distance and height between the equipment and the work face
• angle and direction of the nozzle

All of these factors including equipment pressure should be selected and adjusted to suit the substrate and soiling for each individual case.

The following should be considered for the washing process:

• Fan or cone jet nozzles of 25º minimum should normally be used for low pressure washing (hot or cold water)
• Water and type of nozzle should be adjusted as applicable to the substrate and its condition
• Pressure, angle and nozzle distance from the surface should be carefully controlled
• Cleaning should be carried out by wetting and softening (rather than cutting with the water)

Low pressure hot water spray (minimum set temperature at 80 degrees)

Glass, putty, paintwork, plastic pipes, window frames, and guttering should be protected when using low pressure hot water spray at a minimum set temperature of 80 ºC.

Medium to high pressure washing (250 to 1000 psi (17 to 69 bar))

This requires a high level of operative control as it can have a cutting and disfiguring effect on surfaces. The technique can break down friable or delicately carved detail and remove aged, but sound, mortar pointing. It should not be used for initial rinse of chemical cleaning agents (as it can cause uncontrolled dispersal of concentrated chemical).

CAUTION: High pressure washing or ‘hydro-blasting’ must not be used on masonry.

Steam cleaning

Steam cleaning should be used for operations that require low water usage (e.g. building interiors) and should be used to remove isolated deposits with suitable solvents (e.g. paint, oil, grease, and chewing gum). Care should be taken that steam cleaning does not cause deposits to move to the edge of the cleaning area, giving an uneven appearance. Trials should be carried out to ascertain the effect of steam temperatures on stone, brick and terracotta. Steam and condensation can cause problems in interiors of buildings.

For further information refer to BS 8221-1 Code of Practice for cleaning and surface repair of buildings and Brick Development Association- Cleaning of Clay Brickwork.