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TECHNICAL DATAHOW PROTECTIVE COATINGS WORK842exmweb.com | 1-800-363-2423 | [email protected] information provided herein is fundamental to an understanding of the conditions that cause corrosion. Destruction of metals by corrosion takes many forms, depending on the nature of the metal alloy; the presence of metal occlusions or other foreign matter at the surface; the homogeneity of its structure; the nature of the corrosive medium; the incidental environmental factors such as the presence of moisture, oxygen, salts and minerals, temperature; and other factors such as stress; oxide scale; porous or semi-porous deposits on the surfaces, built-in crevices, welds, galvanic effects of dissimilar metals; and the occasional presence of stray electrical currents. Corrosion of metals protected by single coat thin film (<.005%u201d) protective barrier of organic coatings are not uncommon in outdoor weather environments. Corrosion of metals protected by single coat organic finishes are more often a result of localized corrosion in areas where the protective coating is breached, areas of thin coverage, or sharp edges. This type of general corrosion will typically manifest itself in the form of light surface corrosion, and attack the metal where protective coatings are thin such as sharp edges or areas where the coating has been breached. Severe corrosion and adhesion loss is more common in cases where the protective coating was applied over contamination caused by inferior substrates, anomalies in the pretreatment processing, or inferior design and fabrication that causes variations in the adhesion properties and protective value of the finishing system. This type of corrosion typically manifests itself in the form of osmotic blistering. Osmotic blistering in specific areas or specific surfaces causing pattern failure areas typically pretreatment process related. All metals will corrode predictably when the substrate metal surface is exposed to the conditions that promote and excel corrosion. The fact is, if it is made from metal, corrosion will occur. Corrosion of organically coated metals with a single coat application will occur over time depending on the quality and type of the metal substrate, pretreatment process and controls, top coat chemistry, and the severity of external environmental stresses. Automobiles corrode, water heaters corrode, lawn furniture corrodes, metal ships and bridges will corrode. All corrosion is not the same. Therefore, the reason why such a varied selection of materials degrades in certain environments are also enumerated, along with the various mechanisms of the attack experienced. To understand how coatings fail, one must first understand what makes organic coatings work. Why do coatings work? In broad terms, they work because they are applied evenly at the proper thickness, adhere well to the substrate, have good adhesive and cohesive strength and integrity, resist weathering and chemical deterioration, and impede the permeability of harmful corrosive agents.