Harjapesu

Harjapesu, meaning brush washing in Finnish, is a surface cleaning method in which a scrub brush or abrasive pad is used to remove soil, oils, corrosion products, coatings, or other contaminants from a workpiece or substrate. The process can be performed manually or by automated equipment and may employ water, detergents, solvents, or emulsions as a carrier.

The technique relies on mechanical action from bristles or abrasive surfaces. Brushes can be natural or synthetic (for example nylon or wire), and pads such as non-woven abrasive sheets provide different aggressiveness. Brushing can be done wet or dry, with hot water and detergents for heavy soils, followed by rinsing and drying. In production settings, brushes are mounted on rotating heads, conveyors, or robotic arms to enhance consistency and throughput.

Applications include surface preparation in metal fabrication and automotive industries, removal of dirt and residues on machinery and tools, and cleaning of concrete, wood, or composite materials. It is commonly used as a pre-treatment step before painting, coating, welding, or bonding, where clean, consistent surfaces improve adhesion and finish.

Advantages of harjapesu include effective contaminant removal, suitability for complex geometries, and compatibility with automated systems. Limitations include the risk of scratching or gouging soft substrates, incomplete removal of very heavy coatings unless combined with other methods, and generation of wastewater or dust that requires handling and disposal. Material compatibility and process control are essential.

Safety and standards emphasize appropriate personal protective equipment, machine guarding, and waste management. The term is used in Finnish industry and is related to broader surface-cleaning practices and surface-preparation methods.