Coating Consultancy

Plates of stainless steel were coated with a thin film of seven different types of oxidative drying oils in order to follow the development charge in mass and volume during 42 days of curing. The plates were weighed in air and in water, and the volumes determined by applying Archimedes’ principle. All of the oils gained considerably in mass, with a maximum of 12% within seven days. The volume, however, decreased with large individual differences from one oil to another. A cold-pressed raw linseed oil decreased in volume by almost 15% whereas the volume of an alkali-refined linseed oil only decreased by a few percent. It is well known that linseed oil-based coatings are prone to crocodiling (surface crack formation), it is suggested that the severity of this phenomenon may be related to the volumetric reduction of the binder during curing. The described method is suggested as a simple means of screening linseed oil binders for formulation and development purposes.

Principal characteristics of cold applied coal tar coatings are considered with respect to applications. After reviewing the prerequisites of surface preparations, criteria for selection with respect to the exposure are considered. Five classes of coatings produced by one or more manufacturers are itemized and their general characteristics outlined. Care in selection of primer is emphasized and types of acceptable primers to be used under coal tar coatings mentioned. After reviewing briefly the problem of water vapor permeability the author discusses the theory of transmission and gives definitions of transmission rate, permeance and permeability. Methods whereby these characteristics may be evaluated with respect to a specific coating are given. Results of an investigation of vapor transmission rates for three classes and one system of coatings are tabulated. Permeance of commonly used building materials is tabulated. Recommended coal tar systems for numerous exposures of piling, pipe, and other metal structures are given. 5.4.5