Zinc Rich Paint versus Hot Dip Galvanising
Written by AZoM
For many years, there has been debate over the relative merits of zinc rich paint and hot dip galvanizing. There has also been debate within the paint industry about the relative merits of one type of zinc rich paint compared to another. This has generated a degree of confusion with end users of these corrosion prevention products as much of the information requires interpretation or may, in fact, be misleading.
Making Valid Performance Comparisons
Hot dip galvanised coatings have been widely used for nearly 150 years. The technology involved in their application has not fundamentally changed in that time. The main coating component (zinc) has also been a consistent component of the coating since its invention.
Thus, a hot dip galvanised coating applied to a piece of steel in 1900 is technically identical to a hot dip galvanised coating applied to a piece of steel in 2000. There is no difference in adhesion, metallurgy or durability. For this reason, hot dip galvanised coatings have established an international reputation for consistent performance based on case history observation of the coating in service for over 100 years.
Zinc rich paints were invented in Australia in the 1930’s. Since that time, the technology has gone through a number of manifestations in terms of binders, fillers and curing technology. The original inorganic zinc rich paints were heat-cured products. This technology was followed by acid-cured, lithium water based, potassium silicate water based, colloidal silicate water based, lithium/potassium (high ratio) water based and solvent based ethyl silicates.
Each of these inorganic zinc rich paint technologies has its own characteristics for hardness, durability, film-build and ease of application and comparison between them is not valid. The zinc rich paint industry commonly uses examples such as the Morgan-Whyalla pipeline as a long-term case history. The technology used on this project has not been used for forty years!
Australian Standard AS/NZS 2312:1994 Guide to the Protection of Iron and Steel Against Exterior Atmospheric Corrosion, lists only two types of inorganic zinc rich paint of the six mentioned in AS 3750 - Inorganic Zinc Rich Paint. It is thus important to verify that the type of zinc rich paint being specified is the same as the type of zinc rich paint being used as a case history example.
How Much Zinc Do You Get?
With galvanised coating, the process involves chemical pre-treatments and metallurgical reaction between steel and zinc which is process, rather than operator dependent. The reliability of hot dip galvanised coatings in protecting steel in a given environment is an order of magnitude higher than that of paint because galvanised coatings never fail in service through application related factors.
Source : https://www.azom.com/article.aspx?ArticleID=1289