Getting Your Epoxy Mix Right: A Complete Guide to Accurate Measuring

By Nick Schade, Guillemot Kayaks Workshop

If you've ever worked with epoxy, you know that sinking feeling when you realize your carefully applied resin just isn't curing properly. Maybe it's stayed tacky for days, or it's cured but feels weaker than it should. Nine times out of ten, the culprit is a bad mix ratio. Getting the epoxy mix right is absolutely critical—mess it up and you might as well start over, because there's really nothing you can do after the fact to fix poorly mixed epoxy.

I've built hundreds of kayaks using epoxy, and over the years I've learned that accurate measuring and thorough mixing are the two fundamental skills that separate successful epoxy work from frustrating failures. While I'm approaching this from a boat builder's perspective, these principles apply whether you're building rockets, creating river tables, or just doing repairs around the house.

Understanding How Epoxy Actually Works

Before we dive into measuring techniques, it helps to understand what's happening at a molecular level when you mix epoxy. Unlike regular glues that simply dry by evaporating water or solvents, epoxy cures through a chemical reaction. Think of the resin as a bunch of blocks and the hardener as a bunch of hooks. When you mix them together, those hooks grab onto the blocks and bind everything together in a tight three-dimensional network.

Here's the critical part: every little resin molecule needs to find its matching hardener molecule. If you have too many blocks, some stay liquid. Too many hooks, same problem—you get leftover liquid embedded in your cured epoxy. This is why you need just the right balance of each component for the mixture to fully cure into a strong, solid plastic.

The Heat Problem You Need to Know About

Here's something that catches a lot of people off guard: this chemical bonding process releases heat. Every time a hook connects with a block, it gives off a tiny bit of warmth. In a small batch spread thin, no problem. But if you mix up a large amount all at once, those little bits of heat can pack together and start warming up the whole batch.

And here's where it gets interesting—like most chemical reactions, epoxy cures faster when it's warm. So as it starts to cure and heat up, it cures even faster, which creates more heat, which speeds up the curing even more. You can see where this is going. It's quite possible to end up with a pot of bubbling, smoking goo if you're not paying attention to batch size and temperature.

Eight Methods for Measuring Epoxy

Over the years, I've used just about every measuring method out there. Here's my rundown of eight different approaches, from the most common to the most specialized.

1. Standard Dispensing Pumps (The Ketchup Pump Method)

Let's start with what most people will encounter first. When you buy epoxy, you'll often get these pump dispensers that look like they came straight from a burger joint condiment station. And honestly, that's basically what they are—ketchup pumps repurposed for epoxy.

I've built hundreds of kayaks using these pumps, and they work great. They're pre-calibrated so one pump of resin and one pump of hardener gives you the correct 2:1 mix (or whatever ratio your epoxy requires). The key is paying attention. Watch for burps or farts that indicate they didn't get a full dose. Make sure the plunger comes all the way back up before you push it down again—give it a little tug if you're not sure.

The downside? They're relatively slow for large batches, and your minimum batch size is one pump of each. But for the vast majority of small to medium projects, these are your go-to solution.

2. Calibrated Mixing Cups

These cups have graduated markings showing ounces or milliliters. For a 2:1 mix, you might pour four ounces of resin and two ounces of hardener—straightforward and simple. The nice thing is you can mix right in the measuring cup, though I like to keep the epoxy down in the bottom third so I have room to really get in there and mix thoroughly without making a mess.

3. Ratio Cups with Scale Columns

These specialized cups have multiple columns with numbers, and you match the numbers to get your ratio. So for a 2:1 mix, you'd fill the first component to "2" in the first column, then fill the second component to "2" in the second column. The columns are calibrated so matching numbers automatically give you the correct ratio.

I'll admit, these can be confusing at first. Your brain wants to go from 1 to 2 to get a 2:1 ratio, but that's not how they work. Once you get the hang of it though, they're pretty handy for scaling batch sizes up or down.

4. Medicine Cups with Pumps

For really small batches, those little graduated medicine cups work great. You can pump epoxy right up to a specific line without worrying about whether you're doing a full stroke. The trick is to then transfer both components into a larger cup for mixing—trying to mix in those tiny cups is asking for spills.

5. Measuring by Weight

This is often the most accurate method, but here's the catch: a 2:1 mix by volume is not necessarily 2:1 by weight. For example, the MAS epoxy I use is 2:1 by volume but 100:45 by weight. You need to check your epoxy's specifications.

The process is simple—put your mixing pot on a scale, hit tare to zero it out, pour in your resin to the target weight, hit tare again, then add the hardener. The challenge is that it's very easy to overshoot your target, and there's no easy way to recover from that mistake.

6. Weight with Percentage Function

Some kitchen scales (like bread scales) have a percentage mode. You pour in your first component, which becomes 100%, then add the second component until you reach the calculated percentage (145% for a 100:45 ratio). This lets you mix up different batch sizes on the fly without pre-calculating amounts.

Sounds great in theory, but honestly, this is tricky. I demonstrated it in my video and overshot the target—suddenly I was at 157% instead of 145%, and that batch had to be thrown away. Use this method with caution.

7. Benchtop Epoxy Pump (The Professional Solution)

If you're going through a lot of epoxy, this is the gold standard. It's a dedicated dual-pump system where both plungers are connected and move the correct ratio distance regardless of whether you do a tiny pump or a full stroke. It's fast, accurate, and incredibly convenient for making variable batch sizes.

The downside? They're expensive, and if they get gummed up or go out of calibration, it can be hard to tell. I've seen situations where an entire class was using the same pump that had gone bad, and everybody ended up with epoxy that wouldn't cure properly. That's a nightmare scenario.

8. Eyeballing It

For thick, high-viscosity one-to-one epoxies (like typical hardware store 5-minute glues), you can just squeeze out equal-sized blobs and mix them together. I usually squeeze both tubes at the same time to keep track of the puddle size. This only works for 1:1 ratios though—don't try eyeballing a 2:1 mix.

The Mixing Part Is Just as Important

No matter which measuring method you choose, you absolutely must mix thoroughly. I like using a deep pot—much deeper than I'm actually going to fill—so I can really get in there and move the epoxy around. Bring it up the sides, scrape it down, dig into those corners where unmixed epoxy likes to hide.

I tend to mix fairly vigorously, which introduces some air bubbles, but since I'm usually spreading the epoxy in thin layers, those bubbles have plenty of opportunity to escape. If you're doing thick pours where trapped air would be a problem, you might want to mix more gently or use a vacuum chamber.

How Accurate Do You Really Need to Be?

Here's some perspective: you're doing a really good job if your ratio is within 2% of the intended amount. For most hand laminating work in boat building, getting within 5% is probably plenty good enough. Most of us aren't building the space shuttle.

When I was demonstrating the bread scale method in my video, I overshot by about 12 grams of hardener—that's about 26% more than I wanted, making the overall ratio off by about 8%. For a non-critical part, I might have been able to get away with it, but I chose to play it safe and throw that batch away.

Tips for Success

Start with larger batches when using pumps. The first pump of resin or hardener may be slightly off due to drips or leaks between uses. Making larger batches with multiple pumps allows those errors to average out.

Keep track of your pumps. The best method is to alternate: one pump of resin, immediately followed by one pump of hardener. Then just look in your pot to see if you need more, rather than trying to remember if you've done five or six pumps of each.

Consider warming your epoxy. You can lower the viscosity by gently warming the jugs with a light bulb or heating mat. This makes the pumps work faster and last longer, plus the thinner epoxy saturates fiberglass more easily. Just remember that warm epoxy kicks off faster, so keep your batch sizes appropriate.

Use your roller tray. Once I've mixed a batch, I pour it into a roller tray. This spreads out the epoxy so it's not such a concentrated mass, which slows down the heat buildup and gives you more working time.

Pre-calculate your weight measurements. If you're measuring by weight, take the time to create a spreadsheet with common batch sizes. Trust me, you don't want to be doing mental math with a jug of hardener in your hand.

Choosing Your Method

Think about how you actually work with epoxy. If you're always mixing the same size batches for repetitive tasks, dedicated measuring cups might be perfect. For variable projects with different batch sizes, I've been pretty happy with the standard pump system—it's worked well for hundreds of boats.

If you need the highest accuracy for critical applications like vacuum infusion layups, measuring by weight is probably your best bet. And if you're going through gallons of epoxy regularly, the benchtop dispenser is a worthwhile investment despite the cost.

For really large projects like epoxy river tables, you might just mix whole containers at a time—two gallons of resin to one gallon of hardener—saving careful measurements for final top-offs. At least you know the ratio is going to be right when you're using whole containers.

When Things Go Wrong

If your epoxy doesn't cure properly, you need to know that there's really no fix. You can't add more hardener or more resin after the fact. If the ratio was wrong or the mixing was inadequate, the only solution is to remove all of it and start over. This is why getting it right the first time is so important.

Slightly off ratios might give you partial curing or an epoxy that hardens but doesn't achieve its full strength. Way off ratios will leave you with sticky, liquid resin that never fully hardens. Neither situation is salvageable once the epoxy is on your project.

Final Thoughts

I've covered eight different methods here, and honestly, they all work. They're not all equally accurate, and they each have their quirks, but you should be able to find one that fits your needs and workflow.

The most important thing is to pay attention. Watch your pumps for burps, double-check your measurements, and mix thoroughly every single time. Build good habits, and accurate epoxy mixing becomes second nature.

If you've stuck with me through this whole guide, I hope you've found it useful. And if you have a measuring system that works for you that I haven't covered, I'd love to hear about it. We're all learning from each other in this community of makers and builders.

Now get out there and make something amazing—with perfectly mixed epoxy, of course.

Happy building!

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Nick Schade is a boat designer and builder at Guillemot Kayaks workshop. He's been working with epoxy for over four decades, building hundreds of wooden kayaks and teaching others the art of boat building. You can find more tips and techniques on his YouTube channel and at guillemotkayaks.com.