Oxalic Acid Recipes to Determine % Strength


Just wanted to get a bit scientific with the recipe. I read a lot of people making OA in a wide range of measurements. Perhaps @CaCO3Girl can chime in a confirm my research.

Aim - To determine a simple calculation to determine strength % of OA solution.

Use - when preparing and using solutions be able to use defined quantities of OA to prepare specific % strength solutions. Rather than mix up a random solution, use, need a “bit” stronger and add “some more”, be able to know what strength you start with, how much to add to increase to another known strength %. This will enable to ability to duplicate results in future applications with consistency.

Using 99.6% pure OA here is what I have determined.

1 Gal water + 3.4 oz OA = 3.2% OA Solution.

If this is true then for simplicity since this is not brain surgery, using 1 gal of water + each oz of OA = the strength of the solution.

1 Gal Water + 1 oz OA - 1 %
1 Gal Water + 2 oz OA = 2 %
1 Gal Water + 3 oz OA = 3%

Is this accurate?

Elemonator and Oxalic Acid?

I’m sorry, but my brain now actually hurts. As one of my old professors would say, how much does a mile weigh? Oh can’t tell me, then why are you comparing weight and volume it’s like extrapolating data on distance as it compares to weight.

When it comes to water you can say 1 gram is equal to 1 mL, because it is. So a gallon of water can weigh 3785.4 g OR 3785.4 mL

Ounce is a different story. Fluid ounce is 29.57 mL But ounce in weight is 28.35 g. Is it a huge difference, no, not unless you are dealing with larger quantities.

Now the other problem is that Oxalic is, for lack of a better word, FLUFFY. You can’t measure it in a cup it has to be weighed in by grams. It also doesn’t like to be in water. It is only soluble at a rate of 143 grams per Liter, or 1000mL…or 14.3% However, it’s been my experience that even if it LOOKS like it’s in, it’s not.

When i mix up Oxalic I use a touch of phosphoric to make it stay in water better. It also helps to add in a touch of surfactant to assist in keeping it together in solution and to clean.
As far as the original question…I’m unclear why you wouldn’t know what you started with.


This reminds me of chemistry classes in college…my brain hurts! Stop please. Jk.

I like the good info


Thanks CaCO3Gril for your response.

I started my research and trying to get answers based on your last statement - “I’m unclear why you wouldn’t know what you started with”. In my best attempt not to offend anyone, that is my point. I do not think anyone really knows what they are starting with. We have passed down some “best practices” based on a fast and loose approach. To support what I have said, these are actual statements from threads relating to Oxalic Acid from this forum.

  1. “I used 1 cup per gallon and it was really “HOT””.
  2. “I usually use 1/2 cup and if I think it needs more I add a bit to it”
  3. I shoot for 6 oz per gallon when I mix it up.

All I am trying to do, it define what it is I am doing so that I do know what I am starting with or using.

Again, in no way do I want to offend anyone especially the certified chemist of the group, but I am not sure what “a touch of phosphoric or surfactant” means? A teaspoon? A tablespoon?

It is great to know that 14.3% is the maximum strength. Anymore than that, we are just wasting chemical/money.

As a refrence, Savagran Wood Bleach (OA) states on package to mix 12 oz (entire package) with 1 gal of water. But again, I have no idea what concentration that is?

AIM - to determine an exact recipe for making OA solution to be as effective and cost efficient as possible with the understanding of how to modify ingredients to increase or decrease concentration strength.

I bet I could ask 95% of the board the recipe to get 1% SH using 12.5% for a pump up sprayer and get an accurate response. From the responses on the board, we have 0% that can do that with OA - this is not to say folks are not getting great results with what they are doing and finally, I am not trying to offend anyone, just want to figure this out like we do with SH.


Lots of knowledgeable and great people here but that might be optimistic! :+1:


Well I can’t go giving my formulas away, LOL!

I think your approach to be repeatable is commendable. However, unless you have a scale with you out in the field the best practice is to pick something that is reproducible, and that will correlate with people universally. For example, a red solo cup or a small mouth rinse cup. Those sizes are repeatable by people in Hawaii and in New jersey.

So your formula could be 1 red solo cup, specify if you packed it down or not, per gallon of water. No that’s not a real formula, but you get my point. If that works for you, then you can weigh out what all actually fits in that cup and get the approximate grammage of what you added, and back calculate with the weight of a gallon of water to get your exact percentage. I recommend you weight your “packed” cup 5 times, while emptying and filling it again, and take the average of those 5 different attempts.

The field isn’t like the lab and the lab isn’t like the field. Adaptations must be made.



Perhaps I am unusual, but I do have a scale and typically once per week i have a weekly routine where I perform maintenance on my equipment and restock my dry chemical supply. On my trailer I have a storage box and inside, I keep pre-portioned bags of chemical ready to mix which I make up during my routine.
I generally keep bags of Sodium Hydroxide, OA, Sodium Precarbonate, etc portioned into bags to mix with 1 gal water and to mix with 16 and 32 oz spray bottles (great way to have flexibility to only make what you need to for a situation as well as simple, easy in the field get it done). I do this so that “in the field” I am not reliant on the red solo cup not getting lost, or leaving on trailer and blowing away,etc. I found this to be a simple and effective way to have what I need, ready to go, so that I am not guessing at what to mix. It also allows me to only keep a reasonable stock of what I need on the trailer (I get 50 lb bags of Sodium Hydroxide and Potash, 20 lb bags of OA, and so on that allow me the best price per lb by buying bulk).

I did find an article that states if you mix 3.15 grams of OA into 250ml of water, you get a .1/M concentration. @CaCO3Girl - how does .1/M (Molarity) translate into what we normally think of as a % solution? or does it even?


It doesn’t. Molarity is based on the molar weight of the chemical substance. So for one mole of water it is 18.015 amu or grams. If you want that to relate to real world percentages you would have to involve Avogadro’s number which is 6.022 times 10 to 23rd power to get to the weight on a human scale…but I’m pretty sure everyone stopped reading by now LOL!


I’m still reading and eating a handful of popcorn with 4.7 molars of butter on it with each post. Now I have actually no idea how much butter that is but I’m still impressed by your knowledge @CaCO3Girl!


So I have done some additional research and would like @CaCO3Girl to validate if she could.

What we use is Oxalic Acid Dihydrate (powdered form). The molecular weight of the active acid is .714/gram.

To build a recipe to calculate a concentration strength % I used the following formula:

(Total weight in grams of OA * molecular weight)/volume weight (ml converted to gram) * 100 to get %.

7.5 grams Oxalic Acid Dihydrate - this happens to be 1 tablespoon (not packed or mounded, just dip it in the bag and level it off).

100 ml water (happens to be 1/3 cup)

Formula -
(7.5*.714)/102/100 = 5.25%

This recipe will yield a 5.25% strength OA solution.

If this logic and understanding is true, then applying this to the real world would give us the following results -

The most common suggestion through anecdotal evidence in comments from forum post is to use 1/2 cup OA per gallon of water. Applying the formula we get the following:

1/2 Cup OA = 60 grams
1 gal water = 1280 ml

(60*.714)/1285*100 = 3.33%.

The results are that when it is suggested to use 1/2 cup OA per gallon of water, it relates to a 3.33% solution strength.

When a poster makes the comment that they used 1 cup and it was “HOT”, they were using a 6.66% solution. Note - this is neither good or bad, just relating what “HOT” means in terms of %. It is still no where near the maximum solubility of 14 % that @CaCO3Girl referenced above. At 14% would be have the equivalent of rocket fuel then? (Metaphorically not literally people)

Off Topic a bit - 1/4 up of OA powder is fatal to humans as it will shut down the liver terminally.

@CaCO3Girl = based on the 1/2 cup OA/Gal = 3.33% recipe and referring back to your comments of a “touch of phosphate and surfactant”, how much of each would you recommend to add to maximize efficiency and effectiveness of the solution in a production environment?

My next step in this learning process is to complete the following experiment:

Using a single piece of aged wood, cleaning using only light pressure and then apply various strengths of OA Solutions ( 1.65%, 3.33%, 4.99% and 6.66% - these % representing recipes using 1 gal of water and 1/4, 1/2, 3/4 and 1 cup OA powder) and applying to sections on the board to provide a results based effect of specific strengths using a constant basis (same board, same dwell times, same rinse times, etc) to determine best strength to use and/or effects of various strengths. The second part of this process, will be the let the board dry and then reapply the solutions to see what effect a second application has.

More to come on the same bat channel, same bat time!


Your molecular weight looked low, so I googled it. Please see attached photo. As for the rest…I’ll have to look into it when I get to work.


@CaCO3Girl - I was using the following excerpt to form the basis of the final OA weight.

The molecular formula of oxalic acid is C2H2O4. The molecular weight of oxalic acid is 90.03 g/mol. However, the oxalic acid you purchase – is the dihydrated form of oxalic acid.

Di as in two, hydrated as in water.

The molecular formula of oxalic acid dihydrate is C2H2O4.2H2O and oxalic acid dihydrate has a molecular weight of 126.07 g/mol.

Therefore the weight of oxalic acid in 1 g of oxalic acid dihydrate is 90.03/126.07 = 0.714 g .

The author goes on to share a OA recipe that produces a 3.2% final solution that is used in bee keeping to kill mites that seem to be a problem for them.

From that article and information, I then built the recipes based on this information to convert grams & ML into tablespoons & cups for ease.

Can you validate or correct this for me?


The molecular weight of the dihydrate is 126.07 g/mol

To get to grams you should look at this tutorial:



You people are not normal :anguished:


So, I finally got back to doing some math on this.

11 grams of OA into 500 ml water = 2% solution. That is the same as saying 1/2 cup OA into 1 gal water = 2 %.
Note - all measurements are not packed or mounded. Just fill the measuring cup to the line and be done like a normal person (@Nashvillewash).

Using 1 gal water with the following amount of OA will equal the %
1/2 cup OA = 2%
3/4 cup OA = 3%
1 cup OA = 4%

So my original calculations were a bit off. To get to 14% as @CaCO3Girl stated was the maximum, one would have to use 3 1/2 cups OA per gallon.

I feel that while the exact calculations might not be 100% scientifically accurate, they are within reasonable range to work with.

Now if it would quit raining, I can test various strengths on sample woods to see the effects and post some pics.


Don’t forget to account for the flux capacitor


I just got done installing the Twisted Transistor on the board for the flux capacitor. Thank goodness I will only need Fuel and not 1000 HP and with any luck won’t end up with an Electric Funeral.


Why not make it eco friendly where it’ll run off banana peels and other waste


@CFH While the saturation point of oxalic is in theory 14%, it’s easier to get it into solution if you add some phosphoric acid. It assists in dissolving the oxalic and makes it play better with water. You won’t get past the 14%, but you aren’t likely to get that high unless you use a solubilizer like phos acid.

A solution of oxalic and water should be water clear. If it isn’t you can try and heat the solution…if that’s not an option that is where the phos acid comes in. In my deck/fence brightener formulas I have a little bit of phos and a little bit of a surfactant with the oxalic. I’ve found that does a better job than just the oxalic and water.


So you are saying we fit right in on this site @Nashvillewash ?