Paint coatings continued failure

The standard of cleanliness which must be achieved has been stated to be that which will allow the subsequent process to be carried out satisfactorily . As an example, the degree of cleanliness required to satisfactorily zinc plate from an acid solution is somewhat higher than that required prior to zinc plate from a high-cyanide alkali zinc solution. This should never be taken as a licence to skimp on surface preparation. However, the arguments over surface-tolerant paint coatings abound and will probably continue. It is to a very large extent true that problems of early failure in metal finishing are traceable to incorrect or insufficient surface preparation. 

A continuous intact film of water-resistant paint forms an effective electrical resistance to the flow of a corrosion current (a resistance of over lO flcm through the film is easily achieved). Underfilm corrosion can then only occur if a channel of electrolyte connecting anode and cathode can be established by local adhesion failure between the coating and the metal substrate. 

Penetrating finishes such as stains and water-repellent preservatives ( 7,8) leave little or no continuous coating on wood surface. Because there is no coating, there is no failure by blistering or peeling. These finishes are ideally suited for rough-textured surfaces difficult to paint effectively. 

Natural weathering such as wind and rain erosion can eventually lead to failure of protective coatings of composites including paints, and the underlying fiber -resin material, if left exposed, is then vulnerable to continued weathering [29]. Water penetration and UV radiation are other factors damaging composites. 

---