Direct to Metal (DTM) coatings are, as the name suggests, coatings that are applied to a metal substrate without the use of a primer. The resin chemistry is normally acrylic or polyurethane depending on whether it is a water-based, waterborne or solvent-based coating. DTMs are applied on surfaces that require little to no pre-treatment. They are commonly used in the non-professional market, when basic corrosion protection is required and/or when a surface aesthetic is not as important (no specific requirement for a high-gloss topcoat or decorative coat).
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In coatings, the use of traditional corrosion-inhibiting pigments gives a matte or reduced gloss finish to the paint. For gloss finishes with better corrosion protection capability, a two-coat system is required (i.e. a primer and a topcoat). The primer coating offers corrosion protection through the use of a corrosion-inhibiting pigment, and the topcoat provides the required aesthetic finish (high gloss). In DTM coatings, the formulator balances the optical properties with the corrosion protection. Standard corrosion inhibitors are usually pigmented materials, and their irregular shape and large size have a significant effect on the optical properties of a gloss coating. Thus, a compromise is usually made between these two features of the coating, as obtaining high gloss and robust corrosion protection in a single coat is not usually possible. This tends to limit the applications of DTM coatings to either protection of assets in less demanding environments (e.g. indoor) or where high gloss is not a key requirement. The challenge for the innovative formulator is how to produce a single-coat DTM system with durable corrosion protection and decorative aesthetic properties similar to a topcoat.