Chalking of paints

DIN 53159 [310] Paints and varnishes - Determination of the degree of chalking of paint coatings by the Kempf method... 

Paint is one of the most common and widely used materials in home and building constmction and decoration (see Building materials). Its broad use comes from its abiHty to provide not only improved appearance and decoration but also protection of a substrate to which it is appHed. Evidence of the historical uses of paint goes back over 25,000 years to cave paintings found in Europe. The Bible describes pitch being used to coat and protect Noah s Ark. Over 10,000 years ago in the Middle East, various minerals and metals such as lime, siHca, copper and iron oxides, and chalk were mixed and reacted to produce many colors. Resins from plant sap and casein were also used. Over 2000 years ago in Asia, resins refined from insect secretions and sap from trees were used to make clear lacquers and varnishes (2). 

Abkbnunling, m. derivative descendant, abkratzen, v.t. scrape off, scrape, abkreiden, v.i. (of paint, etc.) chalk, abkriicken, v.t. rake off. 

In considering exposure tests, whether in the form of laboratory, field or service tests it is important to consider the purpose of the test and the relevance of the data to the anti-corrosion function of the coating. Thus, in the case of paint coatings, factors such as gloss deterioration, chalking and colour retention are of considerable importance in some industries, for example the automotive industry, but perhaps of minor importance in the painting of structural steelwork. These assessment factors can nevertheless be of significance since they may be the precursors of corrosion of the basis metal. 

Pappas SP, Fischer RM. Photo-chemistry of pigments Studies on the mechanism of chalking. J Paint Tech 1974 46 65-72. 

Two coats of these paints were applied 5 h apart over a heavily chalked latex paint on a white pine board. Because significant differences have been seen between individual chalky test substrates, common control paints containing unmodified HASE, (hydroxyethyl)cellulose (HEC), and HEUR thickeners were included in each test. Test paints were dried for 18 h at 25 BC and 50% relative humidity and then placed in a fog box for 5 h. (The fog box is a Plexiglas (poly(methyl methacrylate)) box with six spray nozzles on the inside top that continuously spray a fine mist of water over the painted panels placed about 15B off the vertical in racks about 10 in. (1 in. z 2.54 cm) below the nozzles.) We used two different fog boxes one sprayed deionized water and one sprayed tap water. 

Ionic cross-linking of the water-sensitive carboxyl groups in the HASE thickeners (and probably other carboxyl groups in the paint) with either low levels of zinc oxide in the mill base or post-added zinc ammonium complexes can be effective in improving the early blister resistance of HASE-thickened latex paints over heavily chalked latex paint surfaces. Of the zinc ammonium complexes evaluated, the zinc ammonium carbonate and bicarbonate ap-... 

Standard Test Methods for Evaluating the Oegree of Chalking of Exterior Paint Films... 

Chalking Formation of a dry, chalk-like, loose powder on or just beneath the surface of paint film or plastic caused by the exudation of a compounding ingredient such as pigment, often as a result of ingredient migration to the surface and surface degradation. 

Because of the property of lead pigments to chalk, and therefore provide an endlessly renewable surface, they were also noted for the brightness of color they produced. Even today, lead chromate is the constituent of the yellow paint that marks curbstones, fire hydrants, and highway guidelines. Sadly, little did anyone realize at the time that, in addition to flaking and peeling, the chalking of lead paint would produce deadly layers of lead chips and dust inside painted homes. 

Australian children exposed to chalking Pb paint Acute and chronic encephalopathy, peripheral motor and sensory neuropathy, ocular neuritis First modem documentation of young children as at high risk for Pb paint poisoning Gibson et al. (1892), Gibson (1904)... 

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