Epoxy Facts

Epoxy Facts

1. 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 (exothermal) and hardening the mixture into an inert, hard ‘plastic'.

3. Epoxies yellow, chalk (or more commonly 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 urethanes that will retain their color and attractive gloss.

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 10 degrees C. 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. After the epoxy has cured, it can handle temperatures well below minus 20 degrees C.

8. Epoxies will begin to soften at about 70 degrees C, 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 using Novalac resins for Higher Heat & Chemical Resistance.

9. Does your epoxy Part B use cycloaliphatic curatives? The best epoxies do! Does the epoxy blush (also known as Amine Blush, Epoxy Blush, Blush)? Blush is a waxy layer that forms on the surface of cheaper epoxies when they cure. Benefits of Cycloaliphatic”

Cycloaliphatic are known for their: improved 'weather ability', water/moisture tolerance, and resistance to blushing and better chemical resistance.

10. There are special epoxy formulations that have increased chemical resistance, increased temperature resistance, the ability to be applied to damp surfaces, 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 and/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'.

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).

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. 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.

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.

16. Always mix the epoxies in one container then pour it into a second container and apply it from the second container. The reason is that mixing is never very good at the corners, edges and sides of the mixing container. If you apply the epoxy from the primary mixing pail you will certainly get some of the unmixed epoxy from the bottom or sides of the container and that epoxy will not harden. Transferring the epoxy to a second container leaves the unmixed epoxy behind, or blends it into the well mixed epoxy.

17. The difference between polyester (fiberglass) resins (commonly used in fiberglass boats) and epoxy resins: Polyester resins are much less expensive, have very strong fumes, are more porous than epoxy resins, and only sticks really well to itself. For anti-blister marine barrier coats, and bonding to wood, steel, etc. use epoxy resin not polyester resin. Generally epoxies (which are often solvent-free) can be applied to foam products whereas the polyester resins will dissolve these products.

18. End users can thicken epoxy with many things, Selected grades of Talc, fumed silica (Cabosil) and tiny glass spheres, known as E-Sphere ceramic are commonly used.

19. While epoxy floors are very common, for serious and demanding applications the epoxy is either mixed with, or applied under and above, quartz (sand) or aluminum oxide grains. Either way, the result is really a quartz or aluminum oxide floor, held in place with the epoxy. The quartz, is much more durable and wear resistant than the epoxy alone.

20. How thick should your epoxy coating be? Thicker is not necessarily better. A primary way to reduce cost is to use low quality resins and lots of cheap fillers. As a result the thicker coating may be inferior to the thinner, higher quality coating.

21. Epoxies and other paints/coatings should not be applied directly to galvanized surfaces. Galvanization is itself a protective coating, one that works by forming its own protective layer. Epoxies applied to galvanized surfaces will soon peel off. If galvanized surfaces must be coated, be sure to use an approved primer. Aluminum is also another metallic surface that epoxies sometimes have a difficult time getting a good bond to. Aluminum quickly forms an oxide layer (why it doesn't rust) - you need to coat it after sanding before the oxide layer reforms. Also, many (not all) epoxies are very brittle and hard. Many aluminum surfaces tend to flex and when they flex something gives - usually the hard epoxy coating pops off.

22. Fisheyes are areas on a painted surface where the coating literally pulls away for the substrate leaving a coating-less void or fisheye. Often fisheyes are caused by surface contaminants such as a bit of silicon, wax, or oil. Surface tension plays a big part in fish eyeing. There are additives that can be mixed into the epoxy that will reduce surface tension. Likewise, on wood, applying several coats of solvent thinned epoxy, instead of one coat of un thinned epoxy, seems to work well. Applying a thick coat of epoxy over a contaminated fisheye surface will bury the fisheye but expect the coating to peel away in the future. As a rule of thumb, always suspect some sort of surface contamination as the primary cause of fish eyeing. Pinholes are similar but caused by expanding air bubbles under the still soft epoxy.

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