The applicator must also take care not to add

  • No School
  • AA 1
  • 374

This preview shows page 40 - 42 out of 374 pages.

The applicator must also take care not to add thinning solvent beyond that recommended by the manufacturer, because the paint viscosity may be so slow that the wet films will sag and run. Over-thinned paint that is applied at too low a film build may result in films that are too thin and have no hiding power. Additives Additives make up only a small proportion of any paint. Yet without these chemicals the paint could not deliver all of its potential performance. Paint additives are used to aid pigment grinding, stabilize resin and pigment dispersions, break foams, aid flow, prevent film surface defects, catalyze chemical reactions, prevent oxidation, enhance adhesion, provide slip and abrasion resistance to the film surface, prevent corrosion, and to improve weathering resistance and enhance color retention.
Image of page 40
PAGE 29 SYSTEMS These additives can be inexpensive or can be the most expensive component on a per pound basis of any ingre- dient. In these days of cost competition, it is not unusual for a paint manufacturer to cut costs by leaving out one of these vital ingredients. Sometimes the effects may not be known until years after the paint application. For example, in a high performance polyurethane topcoat, it is usual practice to add antioxidants and UV absorbers to enhance the weathering resistance. If theses additives are left out of the formulation to lower cost, instead of the ten years of gloss and color retention, only one or two years might be expected. It is imperative that expect- ed paint performance be listed in the job specification. TYPES OF COATINGS Zinc-Rich Primers Zinc has been the most successful coating material for steel protection. The English started with the idea of using zinc dust in organic vehicles to provide a zinc-rich coating. A com- pletely different concept was started in Australia where the inorganic zinc-rich materials were developed. The idea of incorporating zinc dust into an organic vehicle coincided with the time that the more sophisticated synthetic resins became available. Two categories of zinc-rich primers are available based on the binder chemistry. Inorganic zinc coatings are com- posed of powdered metallic zinc mixed into a reactive silicate solution. Those formed from sodium silicate, potas- sium silicate, lithium silicate, colloidal silica, the various organic silicates, and even galvanizing, are reactive materials from the time they are applied. The second category is organic zinc-rich primers, the binders of which are based on organic or carbon-based compounds. Organic vehicles include phonoxies, catalyzed epoxies, urethanes, chlorinated rubbers, vinyls, and other suitable resinous binders. One very important characteristic of inorganic zinc coatings is the electrical conductivity of the matrix. Electrons formed by ionization of zinc at any point within the coating can migrate to the steel substrate and provide cathod- ic protection to any steel area that may be exposed. Particle-to-particle contact of the zinc pigment is not required for conductivity in inorganic zinc coatings since it is in a conductive, organic zinc-rich matrix. Organic rich coat-
Image of page 41
Image of page 42

You've reached the end of your free preview.

Want to read all 374 pages?

  • Fall '19
  • Structural steel

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors