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What is an Epoxy Coating?

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  • Originally Written By: James Corey
  • Revised By: C. Mitchell
  • Edited By: C. Wilborn
  • Last Modified Date: 28 August 2016
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An epoxy coating is a type of thick protective material that’s used to cover things, anything from floors and major appliances to small electronics, to protect them from damage or wear. There are many different types of coating available, but almost all are made of epoxy resins, a chemical class of materials more formally known as polyepoxides. Along with being very durable, these resins are also usually resistant to things like rust and chemical corrosion, and as such are popular in a number of different industries and for many different uses. Most are also relatively easy to use. They typically start out as either a concentrated liquid or powder that manufacturers blend, then paint or spray over the surface to be coated. In most cases drying time is relatively quick and reapplication is seldom if ever necessary.

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Main Uses

This sort of coating is popular in many different industries, but is often the most familiar when it comes to home appliances. Many refrigerators, washers, and dryers feature an outside coating of epoxy that gives then a finished shine and also helps them resist marks, scuffs, and other signs of wear. These sorts of coatings are often more aesthetic than anything, but in other settings the resin can also have a more important mechanical purpose. Electronics that are wrapped in coats of epoxy won’t overheat as easily, for instance, and when it comes to pipe insulation the technique can prevent leaks and can strengthen pipe walls against cracks from temperature changes and corrosive liquids.

Biggest Benefits

There are a reasons why manufacturers and homeowners choose this sort of coating for so many different applications. It provides outstanding resistance to corrosive chemicals, heat, and ultra-violet light, for instance; it also exhibits excellent dimensional stability, extreme toughness, and abrasion resistance. In addition, it provides strong adhesion to a wide range of different surfaces, including glass, metals, fibers and numerous other modern materials.

From a Chemical Perspective

Looking at things scientifically, an epoxy or polyepoxide coating is what is known as a “thermosetting copolymer.” It is a copolymer because it is formed from the combination of two different materials, namely an epoxide resin and a polyamine hardener. The hardener is effectively a catalyst that promotes polymerization. The polymerization process produces extensive cross-linking of the two materials contributing to the compound's strength.

Epoxy coating is thermosetting because mixing the resin and hardener triggers polymerization, or curing, that generates heat. The polymerization process can be controlled by carefully varying the proportion of resin and hardener and the prevailing temperature. Some applications benefit from extended curing and high heat. The curing period can vary from minutes to hours or days.

Primary Types

Epoxy coatings and paints are frequently be divided into two broad categories: waterborne coatings and powder coatings. A waterborne epoxy coating is normally cured at ambient temperature. It is typically non-hazardous with low-flammability, facilitating transport and handling. The water base makes clean-up easier.

An epoxy powder coating is usually cured under controlled, high temperature. This is often a common choice for coating the surface of white appliances, such as washers, dryers, refrigerators, and so on. It can also be used to seal things like warehouse floors or the undersides of boats or other small water craft. More sophisticated fusion bonded epoxy powder coatings are used to protect steel pipes from corrosion, particularly for water transmission. It is a high-performance material, the cost of which is usually justified in terms of an increase in the life of the equipment on which it is applied.

Working With the Substance

Getting the right finish with an epoxy resin can take a bit of patience, but it isn’t usually all that difficult. The hardest part is usually getting the proper consistency. Having appropriate tools is also really important in most cases.

Prior to compounding, both the resin and hardener are liquids with low viscosity at room temperature and so can be easily handled. The quality of a finished product can vary significantly according to the precise proportions of resin and hardener used, however. Coatings are widely available in hardware and home improvement stores, but anyone who is unsure of how to complete their project would be wise to get a professional tutorial before beginning, and hiring an expert to do the job is often the safest course for any true beginner.

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anon988677
Post 1

I have a condo management firm and typically we contract all work out. A few years ago we contracted the re-painting of exterior metal railings to a painter who specified that they would remove loose rust, and then prime and paint with rust paint. The rust later returned within a year.

This year, I've discussed the subject with many others, who convinced me that the way to go is the use of a “rust converter”. The brand ‘Qurox’ was recommended although the idea as I understand it is relatively standard…an organic acid (usually tanned acid) mixed with a co-polymer, and the combination reverses the oxidization and seals the metal, acting as a primer.

The manufacturer recommends scraping/grinding loose ruse

off, then applying three thin coats of the product, with an hour to dry between each coat. Although they are not in the paint business, he recommended that we complete the job with one coat of epoxy paint.

Our painting contractor (different person from prior years) agrees with all of this, expect for the epoxy paint. He commented that epoxy paint is excellent, but is also very expensive and he didn't see the benefit from the added expense, especially in light of three coats of rust converter.

We’re in Canada, where oil-based paints will be largely removed from the market by next year. Our painting contractor recommends using as much oil based paint while we still can.

He didn't mention this, but one possible consideration is that the original paint (seven years ago) is oil-based paint. Since we won’t be stripping, and the only primer will be the rust-converter, is it fair to say that oil-based would work better? And if we were to move to epoxy paint, we would either need to strip the existing oil-based paint, or prime it with something in addition to the rust converter?

A final consideration, I read that epoxy paints, while strong, don’t hold up well to ultraviolet radiation. These metal railings get a lot of sun.

Thanks for any suggestions.

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