Final answer:
The preferred method for removing rust, scale, and dirt from metals before hard surfacing involves using chelating agents, such as citric and phosphoric acids, along with surfactants and abrasives. For cleaning concrete, diluted muriatic acid is commonly used. Properly cleaning surfaces ensures better adhesion and durability of the hard surfacing applied.
Step-by-step explanation:
The preferred method to remove rust, scale, and dirt before hard surfacing relies on the use of specific cleaning agents and techniques that are effective and efficient for the type of contamination present. For ferrous metals, using cleaners containing chelating agents like citric and phosphoric acids, which are nonaggressive, along with abrasives and surfactants, such as modified fatty alcohols, is typically favored. These cleaning agents help in dissolving the rust and detritus without harshly affecting the metal's surface.
Muriatic acid (HCl) is another widely used cleaning agent for certain surfaces like concrete, where it is required to be diluted before application to safely remove scales and deposits. This form of acid cleaning is beneficial for its ability to effectively clean without causing undue damage to the surfaces being treated. Ensuring the metal is clean and free from surface contaminants like rust, scale, and dirt is essential before proceeding with hard surfacing to guarantee optimal adhesion and the longevity of the surfacing work.