While WEST SYSTEM (r) epoxy has a lengthy shelf life, its handling properties and cured strength will deteriorate with time. Although the cured strength of older epoxy may be sufficient for most applications, it's best to use epoxy that's less than a couple years old for essential structural joints. Older epoxies may not have enough heat resistance for some industrial applications such as welding.
As long as you use it properly, old epoxy should be just as effective at bonding new materials together as fresh resin. Just make sure that you don't contaminate your project with dry sand or dust unless you want your work to look like this:
The key thing is to keep old resin clean so that any contaminants don't find their way into your project. If they do, they'll probably show up in areas where glue lines are visible. The good news is that you can usually remove old resin with ease if you take care of your projects.
Old resin may appear dark colored, but this is only because it contains more impurities than newer resin. It's safe to use old resin as long as it hasn't been exposed to sunlight for several months.
You should also know that older WEST SYSTEM resins are thicker than their younger counterparts. This means that you may need to add more liquid resin to get the same thickness as young resin.
Epoxy has a shelf life, and its physical qualities alter over time. Epoxy producers advise against using epoxy that has beyond its expiry date. As with any chemical product, the longer an epoxy resin is exposed to air, light, and heat, the more likely it is to break down and lose some of its properties. The curing agent also has a limited lifespan. When mixed together, these two components are expected to remain stable for several years if stored in the dark at room temperature.
As epoxy gets older, it may become less flexible or even brittle. This can be corrected by simply adding more curative, which will mix into the old material to make a new layer. Older epoxies may also need additional filler added to them to bring back their weight per square foot.
As long as both component stay fresh, the epoxy should keep its strength for many years.
Here are the estimated average duration periods that epoxy products may retain their strength:
At least 10 years for most clear top coats
Between 5 and 10 years for most colored epoxies
Between 3 and 5 years for most adhesive resins
When resin and hardener are correctly maintained at room temperature and in closed containers to prevent contamination, epoxy shelf life can last several years. Those who have worked with polyester resin know that it has a six-month shelf life before it degrades into a worthless jelly-like material. When exposed to light, heat, and air, polyester resin will eventually go bad.
Two-part epoxy has an even longer shelf life than polyester because there is no chemical reaction taking place when it's stored in the bottle. However, once you open the container, the two parts must be used within one year because the catalyst will become inactive after being on tap or in contact with moisture for so long.
There are two types of catalysts used with two-part epoxy: acid catalysts and base catalysts. Acid catalysts include methanesulfonic acid, para-toluenesulfonic acid, and trifluoromethane sulfonic acid. Base catalysts include dimethyl amine, triethylamine, and diazabicyclo[5.4.0]undec-7-ene (DBU).
You should use acid-resistant materials when working with acid catalyzed epoxies. This includes but is not limited to stainless steel, glass, ceramics, and polycarbonate.
Epoxies are more resistant to corrosion and less affected by water and heat than other polymeric matrices. The primary drawbacks of epoxy resins are their expensive cost, lengthy curing time, and handling issues. Epoxy resins are usually mixed at the site and applied as a liquid or cream-like material that is allowed to harden overnight.
They are used in many applications including automotive, aerospace, military, sporting goods, consumer products, and electronics because of its durability and resistance to chemicals and heat. However, they are not suitable for every application because not all components can be cured with epoxides and many require additional steps during manufacturing (e.g., fiber placement).
Epoxies are formed when two or more functional groups are present in one molecule and these groups can connect to each other via covalent bonds. The most common epoxides include glycidyl ethers, oxiranes, and vinyl ethers. These compounds can be monomers or crosslinkers and they all have epoxide groups attached to different atoms. For example, an oxirane has an oxygen atom attached to two carbon atoms while a glycidyl ether has an alcohol group attached to two epoxide groups.
Epoxides are very stable molecules that do not break down in nature.
Epoxy is long-lasting. One of the most appealing aspects of utilizing epoxy outside is its longevity. It may endure nearly half a lifetime if properly placed. If you intend to lay outdoor flooring, epoxy is a wonderful choice. Because of its durability, it is an excellent choice for outdoor patio spaces and pools. Epoxy can also be used in other areas such as walls, windows, and boats.
The quality of your epoxy material will determine how long it will last. There are two types of materials used in creating epoxies: bisphenols and novolacs. Each type has different properties; thus, they are useful in creating products that suit various needs. Novolacs are more flexible but don't stand up to heat as well as bisphenols. Bisphenols have better resistance to heat, but novolacs can be used in things where flexibility is important such as when creating toys.
Generally, epoxies last between 10 and 20 years when placed in proper conditions. This depends on how you use it and what kind of material you use. If you want your epoxy to last longer, you should consider using higher quality materials or adding additional layers to increase its lifespan. For example, you could add a layer of polyurethane after applying the epoxy to create a product that will last longer than just plain old epoxy.
You should also know that environmental factors can affect how long your material lasts.
This is based on more than 30 years of hands-on experience with the items. Until I can show otherwise, I always believe that the reason the epoxy is wearing out or coming loose is because the epoxy is of poor quality, the installation was bad, or both. However, it's possible that someone might be able to apply epoxy over epoxy and have a successful project. Only they would know for sure.