- 2 November 2016
- Posted by: Stm Coatech
- Category: Educational Articles
Epoxies are thermosetting polymer resins where the resin molecule contains one or more epoxide groups. The chemistry can be adjusted to perfect the molecular weight or viscosity as required by the end use. Their are two primary types of epoxies, glycidyl epoxy and non-glycidyl. Glycidyl epoxy resins can be further defined as either glycidyl-amine, glycidyl-ester, or glycidyl-ether. Non-gylcidyl epoxy resins are either aliphatic or cyloaliphatic resins.
One of the most common glycidyl epoxy resins is created using Bisphenol-A, and is synthesized in a reaction with epicholrohydrin. The other frequently used type of epoxy is known as novolac based epoxy resin.
Epoxy resins are cured with the addition of a curing agent, which is commonly called a hardener. Perhaps the most common type of curing agent is amine based. Unlike in polyester or vinyl ester resins where the resin is catalyzed with a small (1-3%) addition of a catalyst, epoxy resins usually require the addition of the curing agent at a much higher ratio of resin to hardener, often 1:1 or 2:1.
As mentioned, the properties of epoxy can be altered and tweaked to fit the desired need. Epoxy resin can be “toughened” with the addition of thermoplastic polymers.
Epoxy coatings are used as industrial floor coatings because of their chemical resistance, durability, low porosity and strong bond strength.
An Epoxy coating consists 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 and hardening the mixture into an inert, hard ‘plastic’.
Epoxy coatings yellow and/or chalk when exposed to UV light especially common when exposed to direct sunlight. This yellowing can be a real problem for some applications. This can be hidden by choosing a darker color of pigmented epoxy. Clear epoxies will yellow and may even cloud up. For this reason epoxies are sometimes top coated with latex, urethanes, and polyaspartics that will retain their color and attractive gloss. This is recommending if color stability or matching colors is important.
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. At the end of the pot life the mixture becomes very warm and further accelerates the hardening.
Epoxy Resins 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.
In theory, a temperature change of 10-15 degrees F. will double or half the pot life and cure time of an epoxy coating. Higher temperatures will lower the viscosity (thin) the epoxy, but also reduce the working time a person has to apply the epoxy.
EPOXY USED AREAS
*Bund walls and floors
*Laboratory floors and walls
*Specialist warehouse and storage areas
*Specialist factory and production facilities
*General purpose adhesives
*As the binder in cements and mortars
*Solidifying sandy surfaces in oil drilling
*Potting and encapsulating media
ADVANTAGES OF EPOXY COATING
*Low shrink during cure
*Hygienic and antibacterial
*Does not contain solvents
*Does not dusting
*Has a wide range of colors
*Excellent moisture resistance
*Excellent chemical resistance
*Good electrical properties
*Increased mechanical and fatigue strength
*Long shelf life
EPOXY COATING APPLICATIONS
To bond well, epoxy requires an even, slightly rough, and totally clean surface. That means patching any potholes and cracks and allowing them to cure fully. Concrete must be at least 60 days old and not sealed for the epoxy to adhere.
Stripping the floor, however, does not clean it. Any grease or dirt will compromise the epoxy adhesion, so cleaning and etching is a step that should not be rushed. Chemical cleaners vary widely, from harsh degreasers and etchers to safer but less effective organics.
- Once the floor is clean and ready for its coating, it all comes down to timing. Choose a day to do the work when the concrete won’t be damp from rainy weather and when the temperature is between 50 and 80 degrees; otherwise the application can bubble and peel. Then, once you mix the epoxy paint and hardener, you only have about 2 hours to work with it, so you’ll need to plan out in advance how best to paint yourself out of the surface, starting in a back corner. The hardest part is waiting: The typical drying time between each step is 12 to 24 hours. And once the whole floor is done, you still have to hold off surface on it for another 72 hours.
Sweep the floor thoroughly to remove dirt and dust. Using an old paintbrush, dust out corners and seams. For painted floors: Using a floor maintainer fitted with a light-sanding pad, scuff the paint to degloss it. Sweep away the dust. Then, using a bristle broom, scrub down the surface with an all-purpose cleaner. Rinse the floor thoroughly and let it dry for at least 4 hours.
For new or bare concrete: Mix the etching solution with water in a plastic watering can, following the manufacturer’s directions. Make sure to wear protective gloves, rubber boots, and safety glasses when working with the chemicals. Wet the floor with a garden hose. Continue etching the floor in small sections. Once you’ve finished the entire surface, rinse the floor with a garden hose, starting in your first corner and moving forward. Continue rinsing until the water runs completely clear. Allow the floor to dry at least 4 hours.
Open both the epoxy paint and epoxy hardener cans. Begin stirring the epoxy paint, then slowly pour the hardener into it. Make sure to scrape out every last bit of the hardener into the paint.
Carefully stir the two components for 3 minutes until they are fully blended. Place the lid loosely back on the can and set it aside, away from the sun, for 30 minutes. The can may feel warm to the touch as the chemicals react with one another
Once the epoxy formula is ready, you must use it within 2 hours for it to cure properly, so work quickly. Always keep the surface well ventilated as you work.
Pour the epoxy into a roller tray fitted with a liner. Using a 3-inch paintbrush, cut in a line of epoxy around the border of the area to be covered, and paint it into seams and corners.
Move to the corner farthest from the exit. Using a 3/8-inch-nap roller fitted with an extension handle, roll a 10-by-10-foot section with epoxy paint. The epoxy should feel slightly thicker and stickier than normal house paint. Rewet the roller and go over the section in a perpendicular direction, again feathering out uneven lines. Continue covering the floor section by section.
Prepare the top coat. Pour the hardener into the clear top coat, making sure to scrape out all of it, and stir the mixture for 3 minutes until it’s completely blended. Place the lid loosely back on the can and set it aside, away from the sun, for 30 minutes. One minute before you are ready to apply the top coat, stir the mixture for an additional minute. If you plan to use antiskid granules, add them now.
You’ll only have about 2 hours to work with the mixture. Using a clean paintbrush, cut in at corners, edges, and seams. Then, using a 3/8-inch-nap roller, start at a point farthest from the exit and roll on the clear coat in 10-by-10-foot sections as you did with the epoxy paint. Work first in one direction, then in the perpendicular direction on each section, making your way forward until the entire floor is covered. The coating will appear white or milky at first but will dry clear.
1.Composite, Thermoplastic vs Thermoset Resins, Date of access: 31 October 2016, http://composite.about.com/od/aboutcompositesplastics/a/Thermoplastic-Vs-Thermoset-Resins.htm
2.This Old House, How to Epoxy-Coat a Garage Floor, Date of access: 31 October 2016, https://www.thisoldhouse.com/how-to/how-to-epoxy-coat-garage-floor
3.Alfaterrazzo, Epoksi Zemin Kaplama Nedir?, Date of access: 31 October 2016, http://alfaterrazzo.com.tr/epoksi-zemin-kaplama-nedir/