15 facts about epoxy coatings1. Epoxy coatings are used because of their outstanding chemical resistance, durability, low porosity and strong bond strength. Better protective coatings are available but not as common, field applied, brush-on, roll-on, or trowel-on coatings.
2. Epoxies consist of a ‘base' and a ‘curing' agent. The two components are mixed in a certain ratio. A chemical reaction occurs between the two parts generating heat (exotherm) and hardening the mixture into an inert, hard ‘plastic'.
3. Epoxies yellow, chalk (or more commonly least lose their gloss), in direct sunlight (UV). The yellowing can be a real problem. For pigmented epoxies select colors that are dark or contain a lot of yellow (such as green). Even clear epoxies will yellow and cloud up. Often epoxies are top coated with latex or urethanes that will retain their color and attractive gloss. This is particularly true if color coding or matching company colors is important.
4. After the two epoxy parts are combined there is a working time (pot life) during which the epoxy can be applied or used. Generally the pot life will be anywhere from minutes to one hour or longer. At the end of the pot life the mixture becomes very warm (or even dangerously hot) and quickly begins to harden.
5. Epoxies will harden in minutes or hours, but complete cure (hardening) will generally take several days. Most epoxies will be suitably hard within a day or so, but may require more time to harden before the coating can be sanded.
6. In theory, a temperature change of 18 degrees F. will double or half the pot life and cure time of an epoxy. Higher temperatures will lower the viscosity (thin) the epoxy, but also reduce the working time a person has to apply the epoxy. Spreading out the mixed epoxy instead of keeping it concentrated in a bucket or container will extend the pot life.
7. Generally epoxies become too thick and cure too slowly to be applied at temperatures below 50 or 60 degrees F. Temperatures in the 60s, 70s, or low 80s, are best. After the epoxy has cured, it can handle temperatures well below zero degrees F.
8. Epoxies will begin to soften at about 140 degrees F, but will reharden when the temperature is reduced. For common epoxies this temperature is approximate upper end of working temperature range of epoxies. Special high temperature epoxies do exist, however.
9. By their nature, epoxies are hard and brittle. Additives can be added to epoxies that make them less brittle, but generally at the loss or reduction of other positive epoxy properties such as chemical resistance.
10. There are special epoxy formulations that have increased chemical resistance, increased temperature resistance, the ability to be applied underwater, (also click here) and enhance resistance to yellowing and UV damage.
11. Epoxies are expensive, but there are ways to ‘water down' the epoxies with less expensive solvents an/or non-solvent thinners. These cheaper, diluted epoxies do not perform as well as the more expensive, unaltered epoxies. Diluted down epoxies are especially common with ‘floor epoxies' where pricing pressures are especially strong. To a large degree you do ‘get what you pay for'. A common non-solvent thinner is a chemical known as nonyl phenol. This chemical is sometimes used in small amounts to make epoxy mixing ratios easy whole numbers. However, cheap epoxies may contain large amounts of this inexpensive chemical. Check your epoxy's MSDS for references to nonyl phenol.
12. Another clue of a cheap epoxy is if it requires haz-mat shipping. Generally the better resin systems can be shipped non-haz-mat. The exceptions are special high temperature and/or more UV resistant epoxies, which often require haz-mat shipping.
13. Other clues of cheap epoxies include ‘induction time' (after mixing the two components the mixture must sit for several minutes to ‘self cook' before being applied), and crystallization of either part A or part B if left sitting for several months (like crystallized honey, simple heating will dissolve the crystals).
14. As they cure most epoxies ‘blush'. Blush is a waxy coating that forms in the surface of the curing epoxy due to moisture in the air. Visit the Epoxy Blush Page. Because nothing sticks to the waxy coating (including paint or additional layers of epoxy) it must be washed off. Most epoxies blush to some degree but some of the very best epoxies do not, in fact, some can actually be applied underwater.
15. The best time to recoat epoxy is within about 48 hours after the initial coat. Because epoxies take days to reach full cure, a second coat applied shortly after the first coat will partially fuse to the first coat rather than forming a simple mechanical bond.