Paint chalking

Paints are designed to decorate and protect surfaces. During normal wear, paint chalks moderately to clean the surface continuously. A hardened paint surface resists sorption by gases, although the presence of relatively high concentrations of 2620 to 5240 SO2 (1-2 ppm) increases the drying... 

Figure 19.11 shows one of the candidate products for such replacement. Calcinated clay is used as an extender in paints. Chalk has very limited effect on opacity. 

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). 

Carbonates and Sulfates Carbonates include limestone, cal-cite, marble, marls, chalk, dolomite, and magnesite the most important sulfates are barite, celestite, anhydrite, and gypsum these are used as fillers in paint, paper, and rubber. (Gypsum and anhydrite are discussed below as part of the cement, lime, and gypsum industries.)... 

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

Most conventional chemical and petrochemical plants do not process many, if any, non-Newtonian fluids. However, polymers, grease, hea y oils, cellulose compounds, paints, fine chalk suspensions in water, some asphalts, and other materials do exhibit one type or another of the characteristics of non-Newtonians, classified as ... 

The normal visible deterioration of a paint coating is by the appearance of chalking on its surface. Chalking is the term used to denote the powdery material that appears as the binder slowly disintegrates and exposes the pigments. 

These materials are now widely used for coating both steel and concrete surfaces that are subject to a particularly aggressive environment (e.g. North Sea oil platforms). There is less validity for their use under normal atmospheric conditions since they are relatively expensive and tend to chalk on exposure to sunlight. However, their use as zinc phosphate, pretreatment or blast primers for blast-cleaned steel which is subsequently overcoated by any other paint system is an extremely valuable contribution to the painting of new steel work. 

In towns which are not heavily industrialised, the life of a paint film may be about equal to that in rural areas, but, because of traffic disturbance, dirt collection from soot and dust will be noticeable earlier. The use of selfcleaning (chalking) paints can overcome the premature loss of some of the decorative effect without noticeably reducing protection. 

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. 

Chalking is that phenomenon manifested in paint films by the presence of loose removable powder, evolved from the film itself, at or just beneath the surface. Chalking may be detected by rubbing the film with the fingertip or other means."... 

---