Epoxies are resins used as coatings and adhesives in a number of applications, including commercial paints. When mixed with a hardener such as polyamine, epoxies react to form hard coatings that resist high temperatures and chemical attack. At PennCoat, we often use epoxy polyamine preparations for painting industrial and commercial spaces that must stand up to wear, chemicals, and contamination.
Characteristics of Epoxy Polyamines
Epoxy Polyamine paints are typically packaged in 2 components:
- Part A is resin containing epoxy polymer. Depending on the paint, it can include solvents, quartz and titanium dioxide. Epoxies contain the epoxide chemical group, which is a cyclic ether containing a 3-atom ring centered by an oxygen atom.
- Part B is a polyamine hardener that helps determine the product’s characteristics when the two parts are mixed. Amine hardeners undergo a reaction with epoxy resin in which the amine, or NH2, groups polymerize with the epoxide groups to form strong, three-dimensional cross-linked networks that have the desired characteristics.
A common commercial paint we use calls for a 4:1 Part A to B ratio. It is composed of 80 percent solids by volume (89 percent by weight) that is dry to the touch in about eight hours. When dry, it has excellent durability and resists abrasion, weathering, direct impact, heat, moisture, salt and other chemicals. When subjected to the ASTM moisture condensation test for 1,000 hours, HPE applied to a steel substrate showed no blisters, rust, delamination or creepage. Mixed HPE weighs 12.9 pounds per gallon.
Substrate Preparation
In general, all substrates should be sound, dry, clean and free of old paint, oil, dust, grease, dirt, loose rust and any other foreign material. If removing old paint that contains lead, be sure to exercise proper safety precautions, including use of a respirator. Sherwin Williams recommends one to two coats of HPE for the following substrates, in some cases after first applying a primer:
- Iron/Steel, with an acrylic or solvent-based universal primer.
Clean the surface with a solvent or by blasting. Remove weld spatter and soften all sharp edges to no more than a 1/4-inch radius. Prime bare steel within eight hours of cleaning. - Concrete block, with a first coat of a block surfacer.
Clean and dry surfaces. Use a filler/surfacer if you require a smoother finish, but be sure to apply it above 55°F. Let the surfacer dry completely. If applying HPE to weathered masonry or porous cement board, make sure to first remove contaminating material with a brush blaster or power cleaning tool. If you wish, you can apply a concrete conditioner to improve adhesion, seal the surface and resist chalking. - Poured concrete
- Aluminum, with a first coat of wash primer or acrylic primer
- Galvanized
Allow the surface to weather for about half a year, remove any rust and then apply a solvent cleaner. If you can’t wait six months to paint the surface, solvent clean it and apply a test-patch for a week to see if it adheres well. If not, remove the patch via brush blasting and wait. Paint on the same day you clean the surface. - Plaster and wallboard, with a first coat of latex primer.
Make sure surface is clean and dry. Set and spackle nail heads, and apply tape and joint compound to joints. Sand spackle and joint compound until smooth and remove any dust. For outside surfaces, use the appropriate exterior grade of spackle. - Wood
Sand and clean the wood, then paint immediately unless it’s raining or more than 85 percent humid. You may have to spot prime knots and streaks. Otherwise, HPE is self-priming.
Application
The mixed epoxy has a pot life of about two hours, so don’t dawdle. Apply in the temperature range of 50°F to 110°F, and at least 5°F above the dew point. Often epoxy paint can be diluted with ethylbenzene/xylene reducer.
- Airless Spray: Use 2,800 psi of pressure through a 3/8- to 1/2-inch hose and a .017-inch tip. Use a 60 mesh filter and reduce the HPE up to 10 percent by volume as needed.
- Conventional Spray: Use a Binks 95 gun with a #66 fluid nozzle and a 69 PB air nozzle. Keep the fluid pressure at 25 psi and the atomization pressure at 60 psi. Up to 10 percent reduction is allowed.
- Brush/Roller: Use a natural bristle or nylon/polyester brush. If rolling, us a 1/4- to 3/8-inch woven nap. Do not reduce.
Each coat should be between 4 and 8 mils thick when dry. It takes about two weeks for the product to fully cure, although you can apply a second coat after 8 hours. Never mix previously catalyzed epoxy with new. Clean up immediately using a reducer.