Post 196 – by Gautam Shah
Natural and Industrially-produced materials require some degree of surface preparations or treatments before being put to functional use or for readying it for the next process. The next processes could be surface application like coating, cladding, mounting, plating, joining, welding, levelling, cleaning, washing, ph balancing, static removal, etc. Surface preparation could involve processes that induce new surface qualities such as textures, ionization, etc.
The surface preparation at simplest level could be checking and assuring, mainly through visual observation and touch-feel that no foreign materials have remained on the surface, and all loose (removable) materials are detached. These simple processes ensure integrity of the surface.
Surface preparation is required for material objects with their own natural or process-formed surfaces. It is also necessary for further processing of material objects and application of surface finish systems.
Surface preparations are physical, chemical and mechanical processes.
- Physical processes are used to remove unwanted particles or materials (such as rust, nodules, residual deposits, dust or grease, lubricants, cutting-oils, etc.) adhering to the surface. Rubbing, air-dusting, vacuum cleaning, wiping, water-bathing, etc. remove such adhered materials. The particles have remained on the surface due to the holding by surface texture, bonding or ion attraction, and horizontal storage. Washing with soap or a surface active agent (surfactant) can weaken the ion attraction break the weak molecular bond generate by-products that can be removed easily.
- Chemical processes include acid-alkali treatments and solvent washing. The processes roughen, etch or smoothen the surface. In many instances the resultant by-product is beneficial or neutral, so allowed to remain on the surface. In other instances a secondary treatment is required just to remove the by-products of the first treatment. Sometimes Surface preparation agents themselves are the primary surface finishes. Such agents cover the surface area as an intermediary film. Such films help in bonding of the final surface finish. Chemical processes also include burnishing, flame-treatments, surface annealing and hardening, cathodic modification, sputtering and material’s depositions.
- Mechanical Processes affect the surface superficially. Cleaning the surface by removal processes include abrading, grinding, rubbing, blasting, planning, chipping, etc. There are several surface preparation processes that instead of removing materials, only alter the surface with newer textures by engraving, patterning, surface deformation, etc.
- New application of surfaces is made to level or create textured surfaces. Some such processes are integral to art-painting methods. The levelling plasters are made with plastic soils (such as used in pottery), and various qualities of lime or chalk materials. In many instances the powdered mineral and colourants are `loaded’ on a freshly coated `wet’ surface. Colours are also blown as dry powders or applied as pastes and dabbed (pressed) into the wet plaster. Such wet coloured plaster surfaces are then engraved or embossed with textures to facilitate the penetration of colours. Similar techniques are used to produce a bass or relief effects, or provide a highlighting boundary to the drawn object.
- Gesso, a mixture of plaster of Paris (or gypsum) with size, is the traditional ground. The first layer is of gesso grosso, a mixture of coarse, un-slaked plaster and size. This provides a rough, absorbent surface for ten or more thin coats of gesso sotile, a smooth mixture of size and fine plaster previously slaked in water to retard drying. This labourious preparation results, however, in an opaque, brilliant white, light-reflecting surface, similar in texture to hard, flat icing sugar.