One of the most critical aspects of working with epoxy is getting the mix right. If you mess up the mix, the epoxy may never cure, or it will be weaker than it should be. The two aspects of doing the job right are measuring the resin and hardener accurately and then mixing it thoroughly.

In this video, I’m going to show you eight different ways of getting an accurate measurement for mixing epoxy.

Hello, I’m Nick Schade. Welcome to the Guillemot Kayaks workshop. I’m a boat designer and builder. While I am talking about epoxy from the perspective of someone using epoxy for creating boats, the information is applicable to anyone using epoxy for any reason, from building rockets to river tables.

Epoxy starts as a liquid that is generally a mix of two parts: a resin and a hardener. What may be a little confusing is after you mix the resin and hardener together, the liquid you end up with is now also called resin.

Epoxy doesn’t dry like regular glues; it cures through a chemical reaction. There is some fancy chemistry going on that causes the two liquid parts to transform into a hard, rigid, and strong, solid plastic. There is something in the hardener that when mixed into the resin causes them to combine together and become a completely solid material. Every little molecule of the resin must find the compatible molecule of the hardener, and they will bind together. 

The molecules reach out to each other and grab ahold of neighboring molecules and then bond to each other into a 3-dimensional network of atoms. When this happens, the liquid pieces can no longer flow, and it turns into a solid.

The initial resin is like a bunch of blocks, and the hardener are a bunch of hooks. The hooks grab onto the blocks and bind everything together in a tight net. If there are too many blocks, some of those blocks will stay liquid, or if there are too many hooks, some will be left behind as a liquid.

So, not only do the resin and hardener need to be mixed thoroughly so all the hooks can find all the blocks, but there need to be just the right amount of each for the mixture to fully cure. All the little blocks are looking for the perfect match with all the little hooks, and if they don’t find a match, they stay as a liquid embedded in the blob of epoxy.

Your task when you are measuring out the liquid resin and hardener is to make sure there is the right balance of each part so all the blocks will be matched up with the hooks they need to bind into a strong solid.

Like a lot of chemical reactions, this bonding of the chemicals releases heat. Every time one of the hooks makes a connection with a block, it gives off a tiny bit of heat. If all those little bits of warmth are packed tightly together, it could get quite warm. 

This means that if you mix up a large amount of epoxy at once, the mixed epoxy may start to heat up.

And like a lot of chemical reactions, the hooking together of the blocks in the epoxy reaction will happen faster when it’s warmer. So, with warmer conditions, the epoxy cures faster.

Now think about what happens when the epoxy starts to cure, giving off heat. What is that going to do to the bits of epoxy that haven’t cured yet? Those bits are now going to cure a bit faster. This will give off more heat, which will cause the epoxy to cure faster, giving off more heat, making the epoxy cure faster… you get the idea. It is quite possible to end up with a pot of bubbling, smoking goo if you don’t pay attention to the epoxy temperature.

No matter what you are using epoxy for, you will be mixing it in a context where you want to control the amount of the initial liquid resin and hardeners to suit your needs and be able to mix up enough epoxy that you can work efficiently and not waste much because it cured too fast before you could use it in your project.

For this, you want to be able to measure your resin and hardener accurately, make a batch size appropriate to the project, and mix it completely without making a mess.

For example, in making my boats, I often want between one or two cups (250 ml to half a liter). This is usually enough that I can get quite a bit done, but not so much that it kicks off before I have used it all up.

I might choose to use the standard epoxy pumps most of the time, but when I need bigger batches, I might measure with large measuring containers or by weight.

I’ll describe 8 different methods of measuring out your resin and hardener. You should be able to choose one of these as being most appropriate for your needs. I’ll start with one of the more common.

When you buy epoxy, it's very common that you'll see this kind of dispensing pump. They're really handy and typically calibrated. So if you do one pump of this and one pump of that, you get the appropriate mix.

You see these pumps are different. This one has a little shorter throw on it than that one. And so if I do one pump here and one pump here, presumably we get the right amount. One thing to remember, these are essentially ketchup pumps or condiment pumps. So, you might find mustard or ketchup or mayonnaise or something pumped out of these at, you know, your local burger joint. They work. I've literally built hundreds of kayaks using this kind of pump, but they're not guaranteed to work all the time. You need to watch them, make sure they don't burp or fart. But this is the go-to. This is what most people are going to be used to, and they work great.

I've had comments people saying, "Ah, I work in professional shop and they'd never let us use these in a professional shop." Okay, fine. I get it. I have a more professional thing here behind you. I'll show you that a little bit later. But these work. You do want to watch to make sure that they don't burp or let out air, which would indicate that they didn't get a full dose. And when you push them down, they can come up a little slow. We want this to come all the way up before we push it back down again. It's worthwhile just doing a little tug on them, making sure they're all the way up before you go to the next batch.

You will find different manufacturers have different size pumps. These are fairly small. Here's another brand. Same idea, just slightly different pumps. Let's see. These haven't been used for a while. So, let's see if they give me a good dosage here. So, I'm going to push down on this. Seem to come right on out. And this one comes right on out. So, that's probably pretty good. If you see little splat, little burps or farts, that's a bad sign. You probably don't want to use that batch.

So, that just I push down on it and nothing happened. I didn't dispense any of it. Let's see if—Okay, see it's not dispensing. And I'm pumping it a little bit just to get some hardener out to the end of the tube. And now I can give it a full stroke. And then give a full stroke of this. But okay, see it's not going right away. So you do need to watch what you're doing. And now that's a full stroke and a full stroke.

Some people may have noticed I just switched brands here. It's okay. I have reason to know that these two brands are compatible with each other. Now, the downside of these is it's a fairly small amount it dispenses with each pump. So, if I'm making up a large batch, it can take quite a few pumps to fill this up to where I need it. The other pumps on the other brand there, a little bit higher volume pumps, you'll get a little bit more. It'll fill the pot a little bit quicker.

The downside is basically your smallest dosage that you can make in a batch is one pump and one pump. So, if you're making things where the batch is small and you need just a little bit of epoxy, these pumps that are a little bit slower will be better for that. If you're only doing big batches where you need to make a larger volume at a time, the other pumps may be better for that.

So, I'm going to go through several ways of measuring out the epoxy that are all accurate and allow you more or less control over how much you're mixing at a time. The two failure modes for mixing epoxy are you don't get the ratio right, and that's dependent on your measuring technique. The other potential failure mode is failure to mix it appropriately. In all cases, no matter how you measure it, you need to mix it thoroughly.

So, that's getting down into that pot. And I like a deep pot, much deeper than I'm actually going to fill it. I don't want to fill this up. But part of the reason is I want to be able to get in there and mix and move that stuff around. Bring it up the sides a little bit. Then scrape down the sides. Make sure you get deep into those corners. So the corners here, it can be harder to get a stirring stick in there. Get your stick in there and mix it. I tend to mix fairly vigorously. If you're doing epoxy where it matters a lot whether or not there's air trapped in it, you might want to be a little less vigorous. But I'm trying to get this done. And I'm going to be spreading this out in very thin layers and the bubbles will have a lot of opportunity to get out. So, this looks a little bit aerated. That's okay. It's going to those bubbles will have a chance to pop once they get spread out thin.

So again, these pumps are calibrated. So one pump of this is matched with one pump of this. This epoxy happens to be a 2:1 mix. So this dispenses twice as much as this. So one pump to one pump creates the 2:1 mix. There are some brands out there that may give you the same pump but tell you one pump of this, two pumps of that. That's a possibility. Read the instructions of your epoxy. Make sure you're doing it right. Again, these are one pump to one pump gives you a 2 to one mix. Sometimes they will give you the same pumps that are calibrated to the same volume for each pump, but you need to do one pump to two pumps to get that 2:1 mix.

So, the next way you can mix is here we've got a calibrated cup that says 1 oz, 2 oz, 3 oz, 4 oz, etc. You can say, "Okay, I want to make 6 ounces of this with a 2:1 mix. I'll pour in four of one component and two of the other component." That's a perfectly valid way to do it.

These cups are calibrated with another tool that you can use here. This says one one mix or one one. So if you were to use this scale here, you'd fill one component up to the one. And then for the next component, you'd also fill to the next one in the next column. So that will be one to one. If you want twice as much, go to two to two. Three times as much, three to three, etc. So you want to match the numbers here. It's not going one here to two there to get a 2:1 mix. To get the 2:1 mix, we have one to one. That will be twice as much of the first column as the second column.

This gets a little confusing because there's another one there. Some paints and so forth. This happens to come from a paint company, have three components in their mix, and it'll be a two to one to one. So, in that case, you'd go to one here. Then the next component would be another one. And then the third component would be the third one. We're just looking at the first two columns because we just have a two component mix. If we want to have a larger batch, we'll go from two in the first column with the larger component. So the resin, and then fill up to the next two in the next column with the next component.

All right. So, we're at the two there. And then for the next component, we're going to go to the second column and we're going to fill to the two. Okay. Nice. So, this we can mix right in this cup. And so, you see, you have some control over the size of the batch. The smallest batch is always going to be that bottom line. So, if you want really small batches, this system might not work.

So, again, I'm digging down into those corners. You know, this is nice because I can use the same measuring pot as my mixing pot, but dig down into those corners. And again, I wouldn't want to make a, you know, number five here in this mixing cup because that's very hard to mix well without spilling stuff all over the place. I like to keep my resin down in the bottom half or third of the cup so I have the ability to get in there, drive it up the sides, draw it down the sides, and get it well mixed. Yeah, I'm introducing a fair amount of air into this mix, but again, I'm rolling this on plywood in a thin layer and so it's going to have a chance for all that air to rise out of it.

So once I get it mixed, I'm going to dump it into my roller tray. And this roller tray spreads out the area so it's not such a large volume in one place and slows down the reaction time a little bit of the epoxy.

If you are mixing smaller batches, these little medicine cups can come in handy and you can use them in conjunction with these pumps. So, let's say you want to have a six strand mix here or you know 3/4 of a fluid ounce or whatever measurement you want here. So, it's going to be a two to one mix. So, we'll measure up to the four here on one cup up to the two here. See if I got that on camera. So measure up to the four here. That's that line. Now when we use this pump here, we can just fill up to that line. And we're not worried about whether we're doing a full stroke or not. We're just coming up to that line. All right. Right there. And then with the second part, we're just going to come up to the appropriate line on it. And so now you have a good ratio here of 2:1.

And you can just pour this into here. Again, I would be a little cognizant of mixing this in that full cup. And we want to make sure we get everything out of it. So, don't just let it drain out. You want to scrape it out. There we go. And that's everything. But now if I were to try and mix it in that cup there, it's very I have to be very careful that I don't spill some down the side. So instead, it can be useful to transfer both halves to a larger cup. Again, depending on the size batch you're making. And again, scrape it out of there because we're dealing with small amounts here. So a small amount of error can make a bigger change in the ratio. So now we can mix it safely in this bigger cup. And again, mix it thoroughly. Scrape down the edges. Dig into those corners. So now this is ready to use.

So the next way to do this accurately is by weight. And this can often cases be the most accurate. But you need to make sure you get the ratios right. If you have an epoxy that is typically a 2:1 mix, it may not be a 2:1 mix by weight. So here we're just looking. This happens to be the MAS epoxy. I'm using the slow low viscosity laminating epoxy. And so it says mix ratio by volume here is 2 to one A to B, but by weight it's 100 to 45. So 2:1 would be 100 to 50. So for every 100 grams or 100 units, you want 45 units of the other thing.

So by weight you can for example measure 100 pounds, 100 ounces, whatever. I'm going to go for 100 grams. So set my scale to grams and then I'm going to put my mixing pot on there and I'm going to tare it. So even if I have stuff in my mixing pot already, if I hit tare, now it's zeroed. But the thing is how much do I want? So the 100 to one the 100 to 45 ratio is that could be 72 that could be 50 g of the resin and 22.5 g of the hardener, 100 g of the resin to 45 g of the hardener, etc.

So, I'm going to pour some in here and wait till it gets to a certain level. So, going up quickly. All right. So, we're at 60, 72, 91. All right, there's 100.5. So, that works out great. As far as our ratio, we're going to want 45 of the hardener. So, to get to 45, we want 145. Otherwise, we could tare it again. So, by taring it again, I've zeroed it out. And now I'm going to go for 45 here.

All right. I overshot it. It's very easy to do. We're close enough. So you see the value of this is we can mix up kind of any amount we want but it pays—this I did with the spreadsheet. It pays to pre-calculate those. If I had poured in 150 I have this pre-calculated so I know what the next amount is. So this is ready to go. I'll mix that up and apply it to the boat.

So that measuring by weight system works well, but you sort of need to have pre-calculated amounts that you're going to mix up. And you know, you need to sort of know what kind of range you're dealing with. And you do need to be a bit careful as you add your second part to maintain that ratio.

So I need to make a smaller amount right now. So I'm going to take and zero that out. I'm just going to sort of eyeball how much I think I need. All right. Something like that. Now I'm going to hit percentage. So this is a bread scale and I guess in baking bread they often deal in percentage. So we're at 100% whatever that number was. We don't really care but that's 100%. Now we want to bring it up to 145.

All right. I overshot it. But you see how that works and that's a bit tricky. You know, now I've overshot it is at 57%. That ratio is not right. So, I'm not going to use that batch. I will mix it up just so it hardens. And it will probably harden just fine. If your ratio is way off, basically unmixed, you might have partial hardening or you know if it's really unmixed, you'll have liquid and very sticky. If the ratio is starting to get close but still not quite right, then you might have it harden just not getting its full physical properties.

So that weight ratio system is very good as far as getting you to accurate, but you need to be accurate pouring it. And if you make a mistake, it can be hard to recover from. So the other system we have is this pump here. Here we have the resin. Here we have the hardener. And they come out separately. And if you notice the ratio down here of where the cylinder going into this pump is versus a cylinder going into that pump. You see from here to here, this distance is the same. So this distance from here to here is twice this distance. So this is a 2:1 ratio.

If I move this pump handle up and down, the distance these plungers move is in that correct ratio. And the beauty of this is I can just do a little bit of a pump or I can do a full pump and it's still going to be the right ratio. And it's fairly quick, so I can make a bigger batch quite quickly. This is probably the most convenient system as far as adjusting batch sizes, doing it relatively quickly and doing it accurately.

That said, if this thing somehow gets messed up, these little cylinders in here, there's O-rings and check valves and a bunch of stuff going on in there that can get sort of gummed up. If they get gummed up, it can be hard to tell if you're getting a appropriate batch. There's been situations where the pump just wasn't working and in a class situation where the whole class was using the same pump and that pump was out of calibration. So everybody in the class ended up with inappropriate ratios in their epoxy and things didn't harden the way they were expected to harden. And that can be very frustrating in a situation like that or any situation. You know, if the epoxy doesn't harden after you put it on your boat or in your river table or whatever it is you're dealing with, the epoxy, all of it has to come out. There's really nothing you can do after the fact to make that poorly mixed or wrong ratio epoxy fully harden. It's just not going to happen.

This works great, but all these systems have their little quirks about them. Probably the easiest, most accurate is with like some of these deep pour epoxies where people are making a river table and they're using whole gallons. So, you know, if it's a two to one mix, you take two gallons of this and one gallon of the other stuff and you just pour it together. You know, there's a lot of money going into that. But, at least you know the ratio is going to be right. So, I'm just going to apply this last bit to the thing I'm working on and we'll call it a day.

The last measuring method I'll discuss is just eyeballing it. This works fine for many of your one-to-one style epoxies such as a typical hardware store 5 minute type glues. By one to one, I mean the epoxies where you use the same amount of hardener as you use resin. This is easiest with epoxies that are very thick or high viscosity. They push out of the container slowly and you can make a nice blob on a flat mixing surface. Here I'm using G-Flex, which is a 1:1 mix.

If I'm mixing up a small amount, a deli or yogurt container lid makes a good disposable mixing surface. I usually squeeze both dispensers at the same time so I can keep track of how big a puddle I'm making. Often the two constituents are slightly different thicknesses so they might come out of the tubes at slightly different rates, but you can control how hard you squeeze each to keep them coming out at kind of the same speed. I just keep on squeezing until I have what looks like enough. Slight variations in the size of the blobs you create shouldn't be a big deal. This gets mixed up thoroughly and then applied to whatever you're gluing.

The last method of measuring I’ll discuss is just eyeballing it. This works fine for many of your one-to-one style of epoxies such as a typical hardware store 5-minute type glues. By one-to-one I mean epoxies where you use the same amount of hardener as you do resin. For every unit of resin you use, the same amount of hardener is used. This is easiest with epoxies that are very thick or high viscosity. They push out of the container slowly, and you can make a nice blob on a flat mixing surface.

This G-flex is a one-to-one mix. If I’m mixing up a small amount, a deli or yogurt container lid makes a good disposable mixing surface. 

I usually squeeze both dispensers at the same time so I can easily keep track of how big a puddle I’m making. Often the two constituents are different thicknesses, so they might come out of the tube at different speeds, but you can control how hard you squeeze each to keep them coming out at the same rate. 

I just keep on squeezing until I have what looks like enough. Slight variations in the size of the blob you create should not be a big deal. This gets mixed up thoroughly and then applied to whatever you are gluing.

So, there you have it. That is eight ways you can accurately measure epoxy. Hopefully, one of them is appropriate for your needs.

They are not all equally accurate. You are doing a really good job if the ratio of resin to hardener is within 2% of the intended amount. And most of us are not building the space shuttle. While getting the optimum performance out of our epoxy is certainly desirable, it is rare that a perfect measurement is mission critical or a matter of life and death.

For most of the hand laminating that I do in boat building, getting the mix within 5% is probably going to be plenty good enough. When I was measuring with the bread scale, I poured out 12 grams more hardener than I wanted. This is about 26% more than desired and that would make the ratio off by about 8%. For a non-mission critical part, I might be able to get away with it, but I chose to be safe and just throw that batch away.

Notice with all techniques it is probably going to be harder to get an accurate measurement with smaller batches, just because a smaller error is likely to be a larger percentage of the whole mix.

Having some way to carefully control how much you dispense can be key to getting an accurate measurement, so even if you are going to use a scale to weigh out your two parts, you may still want to purchase the standard ketchup pumps because they are easier to control than lifting a heavy jug of goo and pouring it carefully into your mixing cup.

Like I said earlier, I have built hundreds of boats using the standard ketchup pumps for measuring out my mixes. They can fail, but with anything, if you pay attention, you should be able to use them to make accurate measurements.

I do find that for the batch sizes I generally like to make they can be a little slow. You may have noticed that the plunger can take a long time to come back up. If you pump too quickly, before the plunger has reset to the top, you will have problems. So, you must be patient.

With these small pumps, you also need to keep track that you have done the same number of pushes from each of the two pumps. If you squirt out 5 quick pumps of the hardener and then go to do 5 pumps of the resin, you must do all five. If the phone rings in the middle, just keep on pumping. 

The best way to keep track is to do one pump of one and then immediately one pump of the other. For each pump of resin, immediately do one pump of hardener. Then instead of keeping track of the count, you just need to look in your mixing pot to see if you need more for the task at hand. You only need to remember which pump you started with and make sure you finish with the other pump.

I will say that I don’t like to make really small 1-pump batches with the ketchup pumps. Some resin or hardener may drip out of the dispenser or leak back through the gasket between uses, so the first pump of one or the other may be slightly off. Making larger batches with more pumps just allows for any errors to average out between pumps.

While the pumps can be slow, it is possible to make them work faster by warming up the resin and hardener. You can lower the viscosity of both by gently warming them. Setting a lightbulb between the jugs or placing them on a heating mat will make the liquid flow more easily. This allows the fluid to move through the pumps more easily and quickly.

Not only will the pumps work faster, but they will last longer because they won’t be under as much stress from pushing down on them so hard.

If you are wetting out fiberglass or need any trapped air to escape the mixed epoxy, heating up the resin and hardener will allow the lower viscosity liquid to saturate the cloth more quickly and allow air bubbles to rise more easily through the epoxy.

The downside of warm epoxy is that it will kick off and cure more quickly. I don’t mix up bigger batches than I can get completely out of the mixing cup and onto the boat I’m building in about 5 minutes. Depending on the temperature of your shop and the particular cure rate of the epoxy you are using, you want to keep batches small enough that you are done dispensing it in less than 10 minutes. 

On the boats I am building, I am generally spreading the epoxy out in a thin layer to saturate fiberglass cloth. These thin coatings don’t hold or generate much heat, so once the epoxy has been distributed, I can still have a lot of time to work it after it’s been spread out.

If you are doing bigger projects where you need a lot more resin, it may get really old to keep going back to mix up another small batch. In this case, a measuring method that allows you to pour out a large amount at a time may become more desirable.

The little medicine cup can be scaled up to a deli container or bucket if you need really large quantities, but for really big batches like epoxy river tables, you may just be mixing whole jugs at a time and saving the careful measurement for the final topping off.

You may be best served by measuring by weight when you are mixing epoxy for something like a vacuum infusion layup where you need control over both the total volume of the mix as well as a precise ratio. In most cases with this sort of project, you will be able to pre-calculate exactly how much you need for each batch. Using a scale that does percentages allows you to mix up different batch sizes on the fly.

While weighing the fluids is probably the most accurate, you may still want the ketchup pumps in the jugs to help you have good control on dispensing the material into your mixing cup.

The dedicated benchtop epoxy pump is a great addition to your shop if you are going through a lot of epoxy. With a bit of maintenance, it will last a very long time, providing accurate measurements for most projects. They are not cheap but are very nice.

At the other end of the spectrum is measuring thick, 1-to-1 epoxies by eye.  If you are making larger batches, dispensing into measuring cups is probably your best bet. Just be sure to scrape all the goo out of the cups.

So, those are the primary methods I know for accurately measuring epoxy. Think about how you use the epoxy as you choose your method. If you are always mixing the exact same size batches, you may be good with some dedicated mixing cups. I have been pretty happy with the old ketchup pump systems available for many epoxy brands. You can get great accuracy with a kitchen scale, but they can be tricky. If you are going to be mixing a lot of epoxy in varying size batches, the benchtop dispenser pumps are hard to beat.

I will include a list of sources for some of the various solutions in the description. Some may be affiliate links if available. If you have a system that you use that I have not talked about, please tell us about it in the comments.

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Thanks for watching and have fun building.