In the sign industry one of the most widely used epoxy resins is the West System Epoxy. Because of its versatility and durability, old school sign makers frequently select this product for projects.
The West System is comprised of three components: the 105 epoxy resin, a hardener and a filler. Depending on which hardener and filler you select, you can use it to as an adhesive, or as a clear coat or for laminating fiberglass or to repair damage to a surface.
Mixing Epoxy Resin
What’s important when working with any epoxy system is that the resin and the hardener are mixed in the correct proportions. If you happen to mess up the mixture ratios, the resin will not cure and you will end up with a mess on your hands.
Metering out the right proportions is not difficult if you use the West System 300 mini pumps. All you need to remember is to combine one full pump of resin with one full pump of hardener.
After dispensing the two components in a clean container, you must thoroughly mix the resin and hardener together. Whenever you mix any components, make sure that you scrape the sides and the corner at the bottom of the container.
Epoxy is exothermic. After the resin and hardener are mixed a chemical reaction occurs. As the mixture cures, the epoxy gets hot. CAUTION: Larger batches can get really hot really fast.
Difference Between Epoxy Resin and Polyester Resin
NOTE: Epoxy resin and polyester resin are not the same thing. Polyester resin tends to be much stiffer. Another difference is cost. Polyester resin is much cheaper. Epoxy resin, on the other hand, is more flexible and stronger. For extremely demanding applications, a two part, marine grade epoxy resin, such as the West System product, is usually a much better choice than polyester resin. These glues form a very strong bond and stick to just about anything. That can be a big advantage if you are bonding two different types of materials, such as wood and metal or wood and plastic.
Test, Don’t Guess. As a word of caution, if you are bonding two different types of materials it is best to test the bond strength of the dissimilar materials prior to fabrication. While epoxy glues stick to just about anything, there are some low energy plastics, such as polyethylene, that it will not stick to.
Epoxy Resin Hardeners
West System offers many different types of hardeners. The major difference from one harder to another is the rate of speed at which the mixture cures. The 205 hardener, which is very popular, sets up fast. In warm weather environments, you may need a slower setting product, such as the 206 hardener or the 209 hardener. The 207 hardener is a specialty super clear hardener, which you can use in a variety of applications, such as adhesives, surface repairs, fiberglass lamination as well as as a coating.
Epoxy Resin Fillers
The third component is the filler. You must select the right filler for the application. The 405 filler is great for general purpose adhesive applications. Gradually add thickener to the resin/hardener mixture until you attain the desired consistency. For adhesive applications the epoxy should have the consistency of creamy peanut butter.
The high density fillers, such as West System’s 405 or 406, change the structural characteristics of the epoxy, making it either stronger or thicker. These high density fillers become very hard after the epoxy cures, which makes sanding difficult.
By comparison low density fillers, such as West System’s 407, are designed for filling holes or to add mass to a surface which can be easily shaped in a manner that Bondo is used for cosmetic purposes. Lighter weight filler are much easier to sand.
Working with Epoxy Glues
Working with epoxy glues requires a slight change in your fabrication process. Ratios of resin and hardener will vary from one manufacturer to another. Be sure to read the manufacturer’s technical bulletins prior to use. Follow the instructions to the letter. Failure to mix the resin and hardener in the correct proportions can result in product failure.
After you mix the ingredients, the mixture will transform from a liquid to a gel and finally to a solid. You need to work fast because once the resin and hardener are combined the pot life is limited. In some cases you may only have as little as 15 to 30 minutes to work.
If you are bonding pieces together with an epoxy, you must clamp the parts while the adhesive is still in its liquid state. Once the epoxy reaches the rubber-like gel state it is no longer workable.
When edge clamping boards, you just need to snug them together with just enough pressure to hold parts together. Any additional pressure can squeeze out too much glue and actually weaken the bond. You can clean any glue that squeezes between the boards with a putty knife and wiping the surface with denatured alcohol. Cleaning up the glue when it is soft is preferable to having to sand hardened glue.
Until the gel finally solidifies, you can coat the surface with additional epoxy. Even after the epoxy hardens to the point that you can no longer dent the surface with your fingernail, it can take as much as a week for the resin to completely cure.
The open time that you have to work with the epoxy will depend several factors, including the size of the batch that you are mixing and the ambient temperature of your shop. As a rule of thumb, the larger the batch size, the more heat is generated and the faster the epoxy cures. For this reason, it is often better to mix several smaller batches than one big batch.
Epoxy also cures faster as the ambient temperature increases. The optimal temperature is 70°F. For hot weather applications, use a slower hardener. Do not use epoxy when the temperatures of your shop or the materials are below 50°F. Low temperatures can compromise adhesion.
Safely Working with Epoxy Resins
Epoxies are great for bonding many different types of materials, such as wood, metals and plastics. To ensure good adhesion, you must prep the surface, just as you would prep a surface for vinyl application. For optimal results, follow the manufacturer’s surface prep recommendations. When using epoxies, you should also follow the maker’s recommendations regarding safe handling, storage and disposal. Here are some general safety rules that you should follow in your shop:
- Work in a well-ventilated area.
- Use appropriate personal safety equipment including safety glasses, heavy-duty gloves, and an air respirator with a chemical cartridge.
- When sanding cured epoxy, wear a dust mask or air respirator.
- After working with epoxy, thoroughly wash your hands with soap and water.
- Never use a solvent to clean epoxy from your hands.
- Dispose of materials responsibly, in accordance with governmental regulations. You can discard unused epoxy after the mixture has cooled down.
- Generally the shelf life for resin and hardener is about two years. Store these components in a cool, dry place away from sunlight. Storage in a warm environment shortens the shelf life.
For demanding applications, epoxy resin is a great choice. These products are waterproof, solvent resistant and chemical resistant. With respect to service temperature range, epoxy resins withstand extreme heat and cold, which make them great for outdoor applications.