There are many recipes for dry laundry soap mixes on the internet. The recipes typically call for grating a single bar of Fels Naptha or Kirks Castile soap and mixing it with large amounts of washing soda and/or borax and/or baking soda.
Often only 1 or 2 tablespoons (TBL) of this dry mix are supposed to be used per load, sometimes even less. Liquid laundry soap mixes and laundry soap "butters" can be more extreme -- sometimes a single bar of soap is used to make gallons of the mix.
A laundry mix that contains a lot of fillers (including water) and very little soap might be fine for lightly soiled clothes, but it will not efficiently remove accumulated body oil, food and other stains, or greasy soil.
Here are my conclusions after doing some research and practical experiments --
Borax and washing soda function in similar ways. Each of these ingredients helps soap clean better by maintaining an alkaline pH in the wash water so the soap retains its full cleaning power. Borax or washing soda also soften the water by chemically reacting with "hard water" minerals. Which one you use depends on the laundry mix you want to make.
Washing soda is best in a DRY laundry mix. It is more efficient than borax for maintaining alkaline pH and softening water -- as long as the washing soda stays DRY until the point of use. Washing soda degrades over time in a water-based product if it is also exposed to the carbon dioxide in air.
Borax is best in a LIQUID laundry mix. It is not as powerful as fresh washing soda, but borax will remain stable and useful over time in a water-based product. If you want to also use washing soda in your laundry, add dry washing soda separately to the wash load.
Baking soda is ineffective. Baking soda has a pH of about 8. Washing soda has a pH of about 11. Borax will have a pH in the range of 9 to 10 in an alkaline mixture like soapy laundry water. (3) Lye-based soap has a pH in the 9 to 11 range.
As you can see, washing soda and borax have a pH similar to soap. Baking soda has a pH quite a bit lower than soap. For soap to function at its best, the pH needs to be high enough, so use borax or washing soda and leave the baking soda out.
Use plenty of soap in proportion to the other ingredients in a laundry mix. A laundry soap mix is supposed to clean, and soap is the ingredient that is doing the cleaning, so be sure there's enough soap in the mix to do the job.
Use enough of the laundry soap mix and the best water temperature to get the most effective cleaning. If you need to routinely pretreat even minor greasy spots and other stains or your dirty chore jeans are staying dirty despite a good wash, you may need to use more mix per load and/or use warmer water when washing these clothes.
Consider the hardness of your water. If you are washing in especially hard water, the washing soda or borax in your laundry mix may not remove enough of the hard-water minerals. The soap will react with these hard water minerals to create a gray soap scum that can make your whites turn dingy and make line-dried clothes stiff and scratchy.
The ideal solution for hard water is to install a whole house water softener. If that is not an option, try using more laundry soap mix per load and/or adding a separate water softener product.
If these changes still do not work, you may have to go back to commercial synthetic detergents (syndets) because syndets do not form soap scum in hard water like lye-based soap does.
Oxygen-bleach (percarbonate) powder should be added separately. Oxygen-bleach powder reacts quickly and easily with water, so it should definitely not be added to any liquid laundry soap.
Even dry laundry soap contains a small amount of water which can react with some of the percarbonate to reduce its effectiveness. I recommend adding oxygen bleach powder directly to the wash load, rather than mixing it into a dry soap mix.
A chelator in your soap will protect the soap against rancidity but will do little to reduce soap scum. Softened water and/or washing soda and/or borax will be much more effective when soap is used in the laundry, for washing dishes, or in a bath tub full of water. (See "Extra credit" below for more....)
Equipment needed to make laundry soap mix
A food processor is the best way to shred the soap and break it down into a fine powder. Shredded soap is too coarse to dissolve quickly in the washing machine. Some people get around this by soaking grated soap in water right before use and adding this liquid mixture to the washing machine. That's too much messing around for me! I use the food processor to turn the shredded soap into a fine powder that dissolves fast in the washing machine tub.
If I could not powder my dry soap finely enough to use directly in my washing machine, I would make a true liquid soap from coconut oil and potassium hydroxide (KOH) and add this soap along with dry washing soda to each load of laundry. But liquid laundry soap is not the focus of this article.
Safety equipment is also important. The soap and other ingredients in a laundry mix are irritating to the skin, so wear gloves. Washing soda and other powdered materials are also dusty and irritating to the lungs, nose, and eyes. If you have a stove hood that vents outdoors, work under the running hood if you can. Another alternative is to work outdoors in a protected location.
Making the soap
My last batch of soap for the laundry was made with 70% coconut oil and 30% lard, but a soap with 100% coconut oil is an even better choice. Coconut oil soap is a strong cleanser, which is not so good for our skin but is great for clothes. It also dissolves easily, even in cold water.
I use zero superfat and a 30% to 33% lye concentration. At trace, I pour the soap batter into a simple loaf or slab mold and set it in a safe place to finish saponifying. Coconut oil soap saponifies quickly, and it will probably get hot enough to gel (and even crack) without insulation.
If you normally add a chelator such as tetrasodium EDTA or sodium citrate to your soap, include it in your laundry soap to protect the soap mix from becoming rancid. If you do not normally use a chelator in your soap making, this ingredient can be omitted.
Shredding the soap
A soap high in coconut oil should be firm enough to unmold 12-18 hours after it was poured into the mold. That is usually the best time to shred the soap. The soap may still be warm to the touch and perhaps a bit zappy (slightly lye heavy) at that point, but I wear gloves and work with it anyway.
Do NOT let the soap fully cure before processing it into a powder! My goal is to shred and powder my soap when it is firm but still has a pliable and waxy texture, like cheddar cheese. In my experience, that happens anywhere from 12 to 24 hours after pouring the soap into the mold. Experience is your best guide.
I weigh the soap log and record that weight for later use. It is easier and tidier to weigh the soap log than to weigh the shreds afterwards.
I roughly cut the soap log into large chunks that will fit into my food processor chute and grate the soap with the shredding blade in my food processor. You can also use a hand grater or salad shooter.
Sometimes when I start grating, the soap will smear around rather than form clean shreds. If this happens, the soap is still too damp to work with. I let the chunks dry for a few hours to a day and try again.
I spread the batches of shredded soap into large flat pans to cool and continue to dry while I work on the rest of the soap. If the shreds are piled high in a bowl, the shreds in the middle will stay warm and damp enough to stick together. The shreds need to be loose and fluffy.
My original recipe for a dry mixture is about equal parts by weight of soap and washing soda. Shredded soap varies too much for a volume measurement to be accurate, so measure by weight for best results.
Making the mix
Now it's time to make the powdered mix. I change to the blade in the food processor and fill the bowl about half full. Do not over-fill the bowl for most efficient processing. Use about 1/2 soap shreds and 1/2 washing soda. I process the soap mix until the shreds break down into a fine powder. It takes about 30 seconds per batch.
If the soap starts to form larger particles or even ball up in the processor bowl, that means the soap is getting too hot and soft so it is smearing together. The solution is to stop, add a big handful of washing soda, and try again. If the soap still balls up even after adding more powder, spread it out in a pan to cool and dry some more and try again a few hours to a day later.
The powdered soap should be about the size of kosher salt or coarsely ground pepper, so it dissolves fast.
I put the finished powdered mix back into the flat pans to cool and dry. If the soap is not quite fine enough, I may put the mixture back through the food processor to see if it will break down a bit more.
If there is any washing soda left over when the soap is all processed, I blend the leftovers into the cooled soap powder and then package the finished mix in a large tub for storage.
Using the mix
I use 2 to 4 Tablespoons of this soap and washing soda mix per load. I have an HE (high efficiency) washer, and my water is softened.
A lot of people want their soap mix to have enough fragrance to scent their clothes after they are dry. I think a whiff of fragrance makes doing the wash a wee bit more pleasant, but I do not expect nor want much scent to linger in my clothing. Just my preference.
I have added an FO (fragrance oil) or EOs (essential oils) when making the base soap -- exactly like I would scent a regular bath soap. The resulting laundry mix has a nice fragrance, but the scent dissipates and does not scent the clothes.
I have tried adding scent to the food processor while powdering the soap, but the smell around the food processor was overwhelmingly strong, so this is not a particularly good nor safe method. The scent does not linger in the clothes.
Another person shared that he puts 10-15 drops of fragrance directly in the soap dispenser of his washing machine. He says that does leave a scent in the clothes, so this tip might be worth trying if you prefer scented clothing.
I figured the cost to make a batch of my laundry soap mix. My cost included the cost of ingredients plus paying myself the same hourly wage I pay to the ladies who help me in my business. I prefer Tide when I use commercial laundry detergent, so I compared the cost of my mix to Tide products.
Bear in mind that scent is expensive, and this extra cost can really drive up the per-load cost of your laundry soap mix. I did not include the cost of fragrance in my calculations.
My first comparison was my laundry mix with oxy bleach versus Tide with Bleach Alternative. The Tide product costs $18 and will do 72 loads, as stated on the label. Cost per load comes to $0.20 for my mix and $0.25 for Tide. Modest savings.
I then omitted the oxy bleach and compared my basic soap mix to plain Tide which costs $18 and will do 96 loads. The cost for the mix drops to $0.10 per load vs $0.19 for Tide. Definitely cost effective.
There are a couple of issues that make my laundry mix even more cost effective. It is very easy to over measure the amount of Tide per load if I use the cup that comes with this product. I doubt I ever got the full number of loads claimed on the label. I also did not like how my washing machine (top loader HE model) got stinky when I was using Tide regularly. When you factor in the cost of overuse and the cost of that pricey washing machine cleaner stuff, the per load price of Tide goes up.
Extra credit. Why doesn't a chelator do much to reduce soap scum when soap is used for washing dishes or doing laundry?
A chelator like citrate or EDTA in your soap is effective at treating small amounts of hard water to reduce soap scum. An example would be the water that is in your washcloth when you shower or when you "spot wash" a dish with a soapy sponge.
When you wash clothes in a washing machine, wash dishes in a sink full of water, or take a tub bath, there is a lot more water involved, and thus there are more hard water minerals to treat.
The short answer -- It is impossible to pack enough chelator into a soap so it can effectively treat a large amount of hard water.
Here is the long answer that explains the reasons why --
How much chelator is typically added to a soap?
Let's say I make laundry soap with citric acid at 3% of the total soap weight. That means there are 3 grams of citric acid in every 100 grams of soap.
I use about 15 grams of soap per load of laundry. Since citric acid is 3% of the soap, this means I am adding 0.45 grams of citric acid to each load.
How much hard water mineral can this chelator remove?
Using simple chemical calculations (well, simple for a chemistry geek!), I estimate the citrate created by this amount of citric acid will chelate roughly 0.23 grams (230 milligrams) of water hardness, assuming the hardness is all calcium carbonate.
The US Geological Survey says --
"...0 to 60 mg/L (milligrams per liter) as calcium carbonate is classified as soft [water]; 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard..." (1)
The hardness of my water is about 100 mg/L (somewhere in the moderately hard range.) The citrate in my 15 grams of laundry soap can treat the hard water in 2.3 liters (about 2.5 quarts) of water.
How much water is used to wash a load of laundry?
"...Most high-efficiency washers use only 15 to 30 gallons (56.8 to 113.6 L) of water to wash the same amount of clothes as older washers [using] 29 to 45 gallons per load (109.7 to 170 L). The most efficient washers use less than 5 gallons (18.9 L) per cubic foot of capacity...." (2)
I have a high efficiency washer. I'm going to assume the actual water per wash load is 56 liters (15 gallons).
How much citric acid is needed to soften this amount of hard water?
I calculated the 3% citric acid in my 15 grams of laundry soap is able to soften 2.3 liters of water. But I need to soften 56 liters of water!
I would need to use 56/2.3 = 24 times more soap to each load to get that much citric acid into the wash water. That is 15 grams X 24 = 365 grams of soap.
This is an unrealistic amount of soap to use per load of laundry.
Another approach would be to add more citric acid to the soap. I would have to increase the citric acid content in the soap recipe from 0.45 g per load to --
0.45 g X 56/2.3 = 11 grams citric acid per load
That increases the citric acid content of the soap from 3% to a whopping 73%. This is not a good idea.
Rather than add citric acid to the soap, a person might wonder, "Why not add the citric acid directly to the laundry water?" Near the end of this article, I explain why this is not a good idea either.
So why is washing soda or borax a better choice than a chelator?
Washing soda or borax is added separately from the soap, so you can use as much or as little as needed to get the results you want.
Washing soda and borax are less expensive and there are fewer environmental concerns compared with some chelators, such as EDTA, typically used in soap.
How much washing soda to use?
Very roughly speaking, washing soda can remove about its own weight in hard water minerals.
My water has 100 mg/L of hardness as calcium carbonate (CaCO3). If my washer uses 56 liters of water per load, I need to add at least this much washing soda to soften the water --
Washing soda weight = (1 part washing soda/1 part CaCO3) X 100 mg CaCO3/L X 56 L/washer load = 5600 mg / 1000 mg/g = 5.6 grams / washer load
My laundry mix recipe calls for a 1:1 ratio of soap and washing soda by weight. I use about 30 grams of this mix per load. So for every 15 grams of soap I add per load, I am also adding 15 grams of washing soda.
That's about 2.5 times more washing soda than is strictly needed for softening the water. (I explain why in the section after next.)
How much borax to use?
Borax is not as efficient at softening water. Very roughly 4 parts borax by weight are needed to remove 1 part hard water minerals.
Since my moderately hard water has 100 mg/L of hard water minerals, that means I have to add about 400 mg/L borax to every liter of water just to soften the water.
Putting that in everyday terms, I would need to add this much borax per load --
Borax weight = (4 part borax/1 part CaCO3) X 100 mg CaCO3/L x 56 L/washer load = 22400 mg / 1000 mg/g = 22.4 grams borax / washer load
It is best to use more borax than is strictly needed for softening. If I use 2 times more, for example, I will want to add about 45 grams of borax per laundry load mixed with 15 grams of soap. That means a borax-based laundry mix should contain 1 part soap and 3 parts borax by weight.
Why not add just enough washing soda or borax to treat the hard water and no more?
Washing soda (or borax) has another job to do in the wash water. It also must keep the wash water alkaline. If the pH in the wash water is not high enough, the soap cannot do a good job of cleaning.
If I add only enough washing soda or borax to just treat the hard water minerals, there will not be enough washing soda or borax to also maintain the pH.
Why not just use citric acid in the wash water to treat hard water?
Citric acid fails at both jobs -- removing hard water minerals and keeping the wash water alkaline.
Any acid, including citric acid, will lower the pH of the wash water below a pH of 7. Soap must remain alkaline (pH above 7) to be a functional cleaner. In acidic conditions (pH below 7), soap breaks down chemically and cannot clean.
Also, citric acid is not a chelator. It must react with a sufficient amount of an alkali, such as sodium hydroxide, to form citrate. It is the chelator citrate that is able to react with hard water minerals.
The reaction of citric acid into citrate cannot happen in a tub of laundry water, because there is not enough alkali present to convert citric acid to citrate.
More discussion on the Soap Making Forum: "Laundry soap and hard water questions"
Note: We sometimes talk as if citric acid is a chelator, as I did earlier in this Extra Credit section, but this is only a shortcut figure of speech, not strictly correct chemistry.
(1) Water Hardness School. Hardness of Water. US Geological Service. https://www.usgs.gov/special-topic/water-science-school/science/hardness-water
(2) Home Water Works. Clothes Washer: Crisp, clean clothes without the waste. Alliance for Water Efficiency. https://www.home-water-works.org/indoor-use/clothes-washer
(3) C. R. Thorston. Chemistry of the Borate-Boric Acid Buffer System. CR Scientific.
March 2013. Downloaded 2 March 2020 from http://www.crscientific.com/experiment4.html
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