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waterborne enamels an oxymoron surely

Architect's memo 51: April 1988

All is well - the paint industry continues its long tradition of obfuscatory nomenclature.

True enamels are coatings made of ground coloured glasses, fused by heat onto metal substrates. In coating terms, they are indeed the epitome; hard, beautiful, enduring, and resistant to some of the most aggressive environments. If they had some flexibility and were able to be applied at room temperature they would indeed be perfect. It is not to be wondered at that paint manufacturers would use such a material as an image for their own products and when, in the early days, linseed oil based paints were hardened by the addition of such materials as Kauri gum, the manufacturers referred to them as being enamellised. The advent, in the 30s, of alkyd resins and the hard thermosetting films they produced became universally referred to as alkyd enamels, or simply enamels.

Acrylic polymers turn up in many guises - Perspex glazing sheets; automotive lacquers and clears; the tough super-durable Uracryl coatings - but their most ubiquitous form is as latex binders for the decorative paint market. The original binders were designed to match existing soft, rubber-latex binders and at this they were very successful. New Zealand pioneered the use of high gloss acrylic house paints and ran foul of the inherent soft nature of the polymers available. Dirt pick-up problems were pandemic as were blocking problems. Blocking is the phenomena of two soft, slightly tacky surfaces adhering firmly together under the influence of pressure and/or heat and there are many windows around that have never been opened since the sixties!

Although the polymer manufacturers responded and produced materials more suited for gloss paints, their inherent thermoplastic nature precluded their use on working joinery shelving and areas where they would come in contact with fatty or oily materials such as kitchens or indeed anywhere that may be handled a lot such as on cupboard doors.

An attempt was made in the mid 80's to produce super-hard acrylics to enter this market. Fundamental flaws in the system lead to their early demise.

It has taken a major technological development in the engineering of acrylic polymers to be able to produce films which compete with the market standard alkyd enamels. The technology involves fundamental changes in how the polymer is assembled sub-microscopically to allow films that form easily yet develop very fast block resistance. Further technology allows subsequent curing to occur, changing the thermoplastic nature of the coating and allowing the development of grease, solvent and sebum resistance. These new materials, having matched alkyds at their traditional strong points, bring additional benefits along. The absence of strong solvent and curing odours is obvious as is the rapid dry time. Less obvious is that fact that the products do not yellow over time, and their exterior weather resistance is far superior to alkyds. This excellent durability now allows a semi-gloss enamel to be used on exterior trim.

Acrylic enamels have arrived to stay. Oxymorons they are not; Resene Enamacryl and Resene Lustacryl they are!

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effects of water and humidity on paintwork

Architects memos
The Resene architect's memo section provides technical information on a variety of topics relating to paints, finishes and coatings.

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