SPRAYING EPOXY (PLEASE DON'T)
Every year we get questions regarding how to spray WEST SYSTEM® Epoxy. Some people want to know how to thin epoxy so it comes out of a spray gun better while others want to know what Personal Protective Equipment (PPE) is required for spraying epoxy safely. We give them all the same answer: Don’t do it! In short, epoxy is extremely hazardous when sprayed.
Why You Shouldn’t Spray Epoxy
To spray epoxy it must be atomized. This means the tiny epoxy molecules will be airborne. You might be saying to yourself, “Of course the particles of epoxy have to be small enough to be airborne Rachael, that’s the definition of spraying it.” Consider other materials you are used to spraying: hairspray, sunscreen, bug spray, just to name a few. Yet, how much of these relatively less hazardous aerosols do you really want to inhale?
To make matters worse, in order to reduce the viscosity of the epoxy enough for a spray gun to atomize it, you must thin the epoxy with a solvent. In general, we don’t recommend thinning the epoxy with solvents as they can decrease the cured properties. In high enough loadings, solvents can affect every stage of the epoxy curing process.
No Sufficient Protection
To play devil’s advocate, let’s say you thinned the epoxy with a low loading of a common solvent. Now, you not only have to concern yourself with the health and safety effects of the atomized epoxy, but also those of atomized solvent. “That’s okay Rachael, I’ve worked with other fiberglass resins that I’ve sprayed so I know I have to wear a mask.” A mask, even an N-95 or a full face mask, isn’t going to protect you from atomized epoxy. Also, a mask only theoretically prevents you from inhaling the epoxy; it doesn’t prevent absorbing epoxy through your skin.
Perhaps you could find a pressurized suit with air provided (not generated, provided) from an outside source. That would help you in the immediate application but then you also have to understand how solvents affect the epoxy’s curing reaction time.
Beware the Green Stage
The epoxy curing reaction is very slow compared to polyester, vinyl ester, or the glues used in spray tack and hairspray. WEST SYSTEM 105 Resin® with 205
Fast Hardener® takes about 60 minutes to gel in a thin film (~1/16" or ~63 mils thick). That means for at least 60 minutes, atomized epoxy that hasn’t yet reached the tacky state can float around the room. Then there are another 6-8 hours during which the epoxy is trying to cure to a solid-state we call the green stage. It’s when epoxy has enough crosslink density to become solid but is still reacting chemically. The 6-8 hour mark is when the green stage begins, assuming your solvent hasn’t affected that too much, not when the green stage ends. The epoxy could stay green for hours to days later. Walking into the shop while atomized epoxy is in the green stage can kick up these tiny particles. Without
a pressurized suit with an external air source hooked up, these epoxy particles pose serious health effects including skin sensitization, respiratory tract irritation or burns, or, as if those weren’t enough, chemical pneumonia.
Overspray of Atomized Epoxy
If you have ever spraypainted something then you know how much overspray there can be, and that’s with a product designed to settle to the surface within 5 or 10 minutes of spraying it. Think of how far small, atomized epoxy particles can travel with that nice summer breeze blowing through the shop, or through the heating system when you’re working in the garage or the basement in the winter.
For the sake of this example, let’s limit the overspray radius to six feet. Now when the epoxy has cured, everything within six feet of the edge of your project is coated with a thin layer of epoxy.
We appreciate our customers and want you to be successful. Contracting chemical pneumonia or having everything in your shop coated with epoxy is not “success” in our book.
The Good News
You don’t need to spray epoxy to get a solid repair or a great-looking part. Just visit westsystem.com and follow our tips on how to properly apply epoxy. Still have questions? Call our Technical Staff weekdays from 9:00 AM to 5:00 PM EST at 886-937-8797 (toll-free).
Cost
Most people notice right off the bat that there is a price gap between the two products. Yellow glues are typically inexpensive while epoxies are more costly. This is a good time to mention that you get what you pay for. Yellow glue is great for many applications but does have its limitations.
Material
This article will only apply to wood applications because yellow glue is inappropriate for work with other materials. When gluing a hem on your dress slacks, you wouldn’t consider using epoxy instead of fabric glue. That being said, the type of wood you are working with could make a difference in which adhesive you may be able to use. Nice dry pieces of mahogany or pine could be bonded with either WEST SYSTEM Epoxy or yellow glue. However, if you are trying to bond oily woods like teak or ipe then WEST SYSTEM Epoxy’s toughness can help you achieve a stronger bond.
Ease of use
It is important to define each adhesive type. Yellow glue can be identified as an aliphatic resin suspended in water. When the water evaporates it leaves behind intertwined polymer chains that bond the two pieces of wood together. This style of resin is a onepart that allows for easy clean-up with water.
All WEST SYSTEM Epoxies are 2-part systems. When you mix the epoxy resin with the hardener at the proper ratio, the two components react, chemically joining and building the polymer network that adheres the pieces of wood together. While epoxies require measuring and mixing (as opposed to one-part glues), they form a stronger polymer network.
Epoxy can’t be cleaned up with water once it is cured but that’s a good thing. The last thing you want is to put your boat in the water and have the glue joints start dissolving. Since epoxy can’t be easily cleaned up once cured, we recommend making epoxy joints as neat as possible before the epoxy cures. Scraping off excess epoxy from your project with a mixing stick and cleaning your tools with solvent before the epoxy cures can save you a big headache later.
Joinery, Gap Filling Properties, and Shrinkage
The tightness or fit of the joint you want will make a difference in the adhesive you should select. Yellow glue works very well when you have seamless joints and the pieces of wood fit together perfectly. Woodworkers commonly use joinery techniques like biscuit joints, mortise and tenon joints, and tongue and groove joints to increase the bonding area of yellow glue while maintaining very tight and sometimes almost imperceptible joints. Also, yellow glue contains a lot of water that evaporates as the glue dries, so it shrinks quite a bit.
Conversely, WEST SYSTEM Epoxy does not shrink when it cures which makes it great for applications where a perfect fit and/ or high clamping pressure is not possible. In fact, epoxy can fail prematurely in very tight-fitting joints or where high clamping pressure creates an epoxy starved joint. We recommend a bond line thickness of approximately 0.01" (0.25 mm) but epoxy can be used in bond line thicknesses up to ¼" (6.35 mm). It is important to note that in thick applications epoxy can generate a lot of heat, which is called uncontrolled exotherm. Contact our technical department if you have questions about the amount of heat generated in a thick (greater than ¼") bond line application.
You can improve epoxy’s gap filling properties in adhesive applications by adding one of our four WEST SYSTEM adhesive fillers: 403 Microfibers, 404-HighDensity, 405 Filleting Blend, or 406 Colloidal Silica. These fillers increase the epoxy’s viscosity, ensuring continuous contact between bonding surfaces and resulting in a strong bond. Another option is to select a prethickened epoxy like Six10® Thickened Epoxy Adhesive or G/flex® 655 Thickened Epoxy Adhesive.
For best results when joining wood with epoxy and fillers, we recommend two-step bonding. This calls for coating the bonding surface with unthickened epoxy before adding thickened epoxy to fill gaps.
Moisture Content
You should understand the moisture content of the wood you are bonding. What is its moisture content during the bonding application and what is the expected moisture exposure of the finished piece? Since common yellow glue is a polymer suspended in water, the wood you plan to bond should be dry in order for the glue to dry properly.
Many woodworking sites recommend a moisture content between 8 and 12%. This is similar to what we recommend for making structural wood bonds with our 105 System. One of our specialty epoxies, G/Flex 655 Thickened Epoxy Adhesive, excels here as it can achieve a structural bond to wood that has up to 18% moisture content. G/flex 655 can even be used to make temporary repairs on damp or wet wood. Once the wood is glued together, you still need to think about the environment your project will be exposed to. There is a good reason boat builders use WEST SYSTEM Epoxy! It offers excellent moisture resistance once cured. Three to five coats of 105 Resin®-based epoxy can dimensionally stabilize wood by sealing it so the moisture content doesn’t change.
Again, since yellow glue is a polymer suspended in water, it generally won’t hold up well in damp or wet environments.