Measuring and Mixing Small Batches of Finish

Here's a long, useful discussion of practical ways to measure out your finish, thinner, and catalyst when you only need a very small amount. April 29, 2013

What do you use when mixing up very small batches of finish? I use CV, but this is for anything that you have to mix, and can't just be poured back into its parent container.

I can't practically formulate less than one quart of CV. But if I don't need that much, it gets harder (and more tedious) to do. I've always thought it would be a great device that could both store the varnish and dispense it; something like a big cooler of ice tea at a picnic. You know what I mean? For absolute accuracy, some sort of metering device would be great, like used for colorants.

I do okay - though I don't like to lift the whole five gallons - with a large funnel into my two-quart pot (whether I am mixing one quart or two). Also, I know the reaction with the catalyst can be stopped by adding 300-400% more straight CV, but I don't have any great way to do that. Is it as simple as just having a clean can on standby?

To summarize, how are you folks getting the product into the pot? What methods are used for mixing very small batches? And for any leftover material, do you have any slick solutions for storing the deactivated, previously-potted varnish?

Forum Responses
(Finishing Forum)
From contributor O:
I mix and spray from a gallon can. I save empty stain cans as I buy the stains in gallons. When I clean up the system (I use AAA), I also rinse out the gallon can and leave some thinner in it so I can get several uses out of it.

I made a stick with notches cut in it to correlate to 1 qt, 2 qt, 3 qt and 4qt. I can then pour from the 5 gallon pail into the gallon can up to the desired notch. I just estimate if I need a pint or 1 1/2 qts. I use a paint mixing cup to measure the catalyst. I also have a small cup that holds 3 oz that I use if I need only 1.6 oz for a pint of material. When I used a pot, I always put the material in a gallon can, and place the can inside the pot so I didn't have to clean the pot, just rinse the can out.

From contributor D:
I had the same problem, as I often spray less than a quart. I went to the drugstore and had a talk with the pharmacist about the math of milliliters vs. ounces. I could have looked this up but I wanted a human explanation. I explained to the druggist what I was doing, she understood. She did some calculations, scribbled some numbers, and gave me the way to figure it. All that to say - you've got to work in milliliters as opposed to ounces.

I made a little spreadsheet chart that I keep on my phone so I can find it. At some point I will print out and laminate a bigger version, but it tells me 1 through 32 ounces, how many ml that is. That then gives me various breakdowns for a percentage, which allows me to pick an amount of CV I want to mix, gives me an amount of catalyst for that amount, and I added a couple of calculations for percentage of thinner I may want to add. Good thing is I can use this same cheat sheet for dyes, toners, etc.

With leftover CV, I've been spraying some nice pieces of driftwood I got from the river that are very dry that I intend to hang up somewhere. I don't know of any other good thing to do with it short of shooting something laying around. I hate to pour out even a small amount, I just see money running out on the ground. I work out of gallon cans I've poured off stirred up product into out of the 5 gallon can.

The sheet is based on an ounce being 30 ml. So if you're using 1 oz of catalyst to a quart of CV, you can do the math. I use Sherwin Williams CV and that's their ratio. I've found I can't really shoot less than 8 ounces total (CV, catalyst, and thinner) in my siphon gun and actually get enough product to work with as the gun needs a certain amount to work. I'm experimenting with a gravity gun to do even smaller batches but while I know it will work, I haven't done it enough to say "yes, this works."

As far as measuring goes, I got some small measuring cups at a local discount store (Fred's) that are really just shot glasses with various markings on them. Using those gives me the ml, and I mix up in a SW measuring bucket that will measure small amounts less than a quart.

From contributor M:
Start measuring in milliliters. If you need to add 3% catalyst, it's easy math.
#ml CV x 0.03 = ml of catalyst required.
A litre has 1000 ml, so add 30ml of catalyst.
If it's 10% catalyst, you just need to move the decimal place. 1432ml of CV... move decimal... 143.2ml of catalyst.

You can buy measuring cups from your finish supplier in lots of different sizes. Get some big ones to pour and measure your CV into, then use a small one to measure and dispense your catalyst into your CV. Now you can pour this off into your spray gun, pressure pot, or simply drop a dipstick from your AAA into it. When empty, let it dry and you can pull the dried material out and reuse the cups. You can get quite a few uses out of a single cup. When pouring into your cup gun or pot, just be sure to use a cone filter.

I buy and keep in stock 1qt (1L) and 2qt (2.5L) cups. I buy them in cases of 100. A case of either size costs me less than $100 from my finish supplier, and they last a long time as they get used over and over until they are finally thrown out. IF you have an MLC distributor, they sell Campy cups and they are already graduated to mix their products.

From contributor X:
The most accurate way to measure catalyst is to weigh it. Just get a digital kitchen scale. When weighing the catalyst, set the scale to read in grams. Weighing takes all the guess work out of catalyzing. You don't have to worry about looking at the measurement right, or whether or not the cup was perfectly level, etc. I made a cheat sheet of how many grams of catalyst per oz. of finish I need. With this method, I can just as easily and accurately catalyze 1 oz. of finish as I can 5 gallons. My finish rep told me he wishes everyone would do it this way, because there would be a lot less problems out there with catalyst.

From contributor J:
Contributor X beat me to it. A gram scale makes life with CV a lot easier. Get the best one you can afford. A good unit will measure accurately down to a tenth of a gram. There are scales that will do better than that, but they get pretty pricey.

From contributor F:
I'm not sure what CV you are using, but MLC is a 10:1 ratio. Easy math. Doesn't matter if it's ounces, liters, gallons, kegs, truckloads or whatever.

From contributor X:
I agree 10:1 makes it easier, but if you need to catalyze a small amount like a few ounces for touch ups or you're just trying to get that last drawer front sprayed, it's hard to measure .2 ounces accurately. That's where weighing it is much easier and more accurate. When catalyzing small amounts, it's not hard to be off 50% when using a measuring cup.

From contributor F:
I never said that weighing wasn't an option. I do it quite frequently while matching paint colors to keep from wasting material, but the questioner only said he needed to mix batches smaller than a quart, which could be done using smaller parts such as ml, tbsp, tsp or whatever. And if accuracy is important, a cheap scale is not the way to go. You can be far more than 50% off with a cheap scale. The scales that go down to a tenth or even better, a hundredth, will set you back. Most shops are not going to spend the necessary bucks to get an accurate gram scale. The one we use was several hundred dollars.

From contributor J:
As far as I am aware MLC is the exception, not the rule, at 10%. Most others are 3% and I would imagine the MLC catalyst is a more dilute mixture than others to make the 10% ratio practical? A 3% ratio is hard to do by volume in small quantities and this is where a scale really pays for itself.

From contributor F:
I agree. Although a different acid, MagnaMax is catalyzed at a little over 2%, but that's done by the distributor. I guess when it comes to what the end user will be catalyzing, they keep it simple. I am a MLC fan for many reasons, but the practicality and ease of use are good issues. In the time that I have spent at MLC talking with their chemist, it seems that ease of use and educating their customers are high on their priority list.

From contributor M:
Maybe I am just lucky, but I am on my second scale from Wally World, and both have been right on the money as far as accuracy goes. Whenever I weigh the catalyst, I pour it into a catalyst cup, so I can visually verify it is the right amount. I also have a 50g weight made just for checking the accuracy of scales, and it is exact every time.

From contributor D:
I appreciate the idea of a scale. I've got one and haven't thought of that, so I've learned something. And not to argue that point, but I sure do like being able to pick up my little shotglass off the spray cart, pour up the material, stir it in and move on. I'm sure the scale would be just as quick if I had it set up. I don't have a good spot for it and I'll have to think on it because I like the idea. I'm certain a scale is exact. But I also know that checking my little pocket reference chart I made, then pouring up X ml of catalyst and X of thinner works pretty good. This has been tested several times when I was very close to being done and needed a small amount to finish up and wanted to mix it up while the rest was still wet - I can mix up a small batch very fast.

From contributor A:
I have used a syringe in both plastic and glass to measure the acid catalyst. Glass will last longer as long as you don't drop it. You can get them at any drugstore or a store that carries livestock products.

From the original questioner:
Thanks! Mixing 2 quarts is easy: 5 gal CV, large funnel, 2 qt pot, 1/4 cup measure catalyst and usually the same amount of reducer. One quart is almost as nice: Same procedure, but using 1/8 cup catalyst and reducer (eyeball 1/2 the 1/4 cup measure).

My visual memory tells me where the CV needs to be inside the funnel for it to be either one quart or two in the pot. These ratios work, as does the visual estimation. I use SW products, and perhaps it's a forgiving system. That is, certainly I am not getting it exactly the same every time I mix up the varnish. In eleven years of using, no problem of doing it this way.

It's when it comes to relatively tiny quantities. Perhaps the whole job is substantially complete, but you forgot about the light rail or two bun feet, or the wood knobs that are being used on one piece instead of the metal ones everywhere else. A quart is way too much, and without being able to practically measure less, I usually relegate myself to the harsh reality of wasting that high-cost product. Grief, it almost hurts to type that! I like the idea of spraying driftwood for art, or whatever else ready-to-finish items for just such an occasion.

Perhaps I should invest in an 8 oz gravity cup for the itty bitty things. For the mixing ratio, it's just a bit of math, sure. So now we're back to getting the 5 gallon can poured into that little 8 oz cup.

Let's talk about plastic a minute. I like the idea of syringes. And the plastic jug that the catalyst comes in holds up just fine. Does anyone see any issue with plastic condiment bottles? The squirty type like you might find at a diner or cafe, red for ketchup (or catsup, if you like), yellow for mustard, or the clear that you, yourself, might already use in your own kitchen to hold olive or vegetable oil. It might be a good break down size for the catalyst, yes?

For the CV, one poster mentioned smaller gallon cans to store in. What are your thoughts on breaking down your 5 gallon can to the gallon size, then swapping the lid for a pour-through type with screw on cap? Provided there wouldn't be any detriment to the varnish to be stored and administered this way, it seems this would provide much better control (for me anyway) when needing to pour out a small quantity into a small cup.

From contributor D:
When I get a 5 gallon bucket, I will stir it real good, then pour off into six one gallon cans, so I don't have a full gallon in any of them since I can't seem to pour out of a full gallon without spilling some but about half the time.

I'm asking SW to shake my next 5, though the manager said he won't pour it off for me and won't let me pour it off in the store since "it might explode." So I'll pour it off on my tailgate and go home. Point is to get it out of that 5 and into something I can handle.

I believe the main criteria for storage is a good seal. Even pouring out of a 1 gallon can is easy if it's not slam full. I usually leave my gallon cans stay about a little less than half and move to next full if I'm making quarts. That way if I need to pour off 8 oz I'm working out of that smaller amount in the half-full can. Make sense?

Go by a discount store, blow a dollar or two on some small cups that will measure ml and try it. You won't need to come up with all these condiment containers then.

From contributor F:
Check with your wood supplier and ask them for some glue bottles. They hold up to thinner, retarder and catalyst. I have had some in the same bottles for years with no problems. As far as dispensing out of the 5, some suppliers can get you a device that you strap the 5 into and just tilt the 5 to pour. That's what I use to pour catalyst so I know it works for CV.

From contributor J:
Another nice feature of measuring by weight is that it can eliminate the need for a mixing cup in small quantities. I put a PPS cup on the scale and strain the material directly into it, use an eyedropper to add the catalyst to correct weight, put the top on, give it a shake and start spraying. No measuring cup, no stir stick, no thinner used to clean up afterwards. And if you can afford a scale that will measure down to tenths of a gram, you can accurately mix as little as an ounce of CV at 3% catalyst ration.