Karla Hooper Earth Girl DIY Soap

DIY Solid Bar Soap

Jan 12, 2020 | DIY, The Earth Girl Lifestyle | 0 comments


I swapped from liquid to bar soap in my early 20’s as a way of reducing both waste and chemicals in my daily life. I never had a desire to make my own as there was a local artisan soap maker that I loved to support and was extremely happy with their product.

Then, I looked up what ingredients they used… and I saw Palm Oil – ‘Sustainable’ Palm Oil (which I don’t believe is a thing), so I immediately set about learning to make my own.

I went to a soap making workshop in August 2018 and it was just what I needed to get me started at home by myself. The original recipe I used contained too many ingredients for my liking, so I set about finding a simpler recipe and learning to formulate my own.

I was looking for a solid bar of soap that didn’t go soggy on the side of my sink, and contained all natural ingredients.

I’m now well and truly an addicted soap maker. It’s such a versatile, creative skill to have, and so practical. I use bar soap for washing my hair, body, hands, clothes and dishes.

Making my own not only saves me a heap of money, but I also love that I can customise recipes to fit my requirements. And best of all, I know exactly what ingredients I’m using in my life and putting down the drain. 

Please note: the information in this blog supports my in-person presentations where I give a live soap making demo. Once you’ve made soap, you realise how easy it is and become confident to replicate the process. However, if you’ve never made soap before, just reading instructions may not be enough. Getting another soapmaker to step you through in person the first time is invaluable for gaining confidence to go solo. 




Solid bar soap is made by mixing an acid (plant or animal fat) with an alkali (a lye solution that’s made with sodium hydroxide and water) to form a chemical reaction called saponification.

Additional ingredients can be added such as scent, colour and texture. The mixture is then poured into a mould and left to set, before being cut to size (if applicable) and curing. Once cured, soap is then ready to use and enjoy. 





The alkali used to make solid bar soap is sodium hydroxide (potassium hydroxide is used to make liquid soap). Sodium hydroxide (which is often sold in a solid crystal form) is mixed with water to create a solution called lye

Be sure to use 100% sodium hydroxide or ensure it states the product you’re buying is suitable for soap making. Also, sodium hydroxide can absorb moisture from the air, for this reason store in an airtight container and only take the lid off to extract quantity needed for soap making and then swiftly replace.


The amount of water used to create the lye solution is subjective. The minimum amount of water needed is the same quantity (by weight) as sodium hydroxide, however, using this amount of water creates a risk of sodium hydroxide crystals not fully dissolving and saponification happening very quickly. Adding more water is safer and makes the process easier. 

Low water soaps saponify more quickly than high water soaps. The more water you use the runnier the soap will be when you pour it into the mould. Excess water will be evaporated out of the soap during the curing phase. 

Use distilled or demineralised water to get consistent results. I get mine from a supplier that allows me to refill my empty 5 litre container when required.


Many different fats, or combinations of fats, can be used to make soap – both from animal and plant sources. 

I personally only use plant based fats, such as oils and butters, and have no experience with using animal fats. I don’t, and never will, use palm oil, which is a very common soap ingredient.

The quality of the fat does not have to be high for soap making, for example, it’s fine to use the refined versions of oils and butters such as coconut, olive, shea etc.

Each fat will bring a different quality (eg hardness, cleansing, conditioning, bubbly, creamy etc) to the soap. 

Saponification Value

Each fat has a specific saponification value (SAP Value), which is the amount of sodium hydroxide needed to saponify the fat used in a recipe. This value is based on an average, which has been determined by taking many samples of the same fat type. For example, Olives can be grown in different climates and soil conditions all around the world. The SAP Value for each batch of olive oil may vary slightly depending on climatic conditions and/or variety of olives used to make oil. 

You cannot exchange the type or quantity of fat within a recipe as doing so would require a new calculation for how much sodium hydroxide is needed. This is very important, because if you use too much lye (aka caustic soda) in a recipe and it doesn’t all get saponified by the fat, it can leave your soap caustic, which could lead to burning the skin.

The easiest way to determine the amount of sodium hydroxide needed to saponify the chosen fat within a recipe is to use an online soap calculator. There are a number available, with my preferred one being www.soapcalc.net

Superfatting / Lye Discounting

To ensure all lye is reacted, an extra percentage of oil is used to superfat soap, this helps to ensure there is no unreacted lye left in the soap and allows for the potential differentiation of SAP Value ranges. The extra fat can also contribute toward additional skin conditioning qualities for the soap. 

Superfatting soap by 5-8% is common, however there are some exceptions to this rule, especially when making pure coconut oil soap, which is extra superfatted to counteract its superior cleansing quality.

In order to superfat a recipe, you can formulate how much sodium hydroxide is needed to saponify the fat/s and then discount the amount of sodium hydroxide used (lye discounting) by the percentage desired OR add extra fat to the recipe (superfatting). Online soap calculators, such as www.soapcalc.net, make formulating these percentages easy.




Natural Scent

You can naturally scent soap by using essential oils. Some essential oils are better to use for soap making than others due to safety, scent retainment and saponification acceleration. 

I personally use and have had good results with rosemary, lavender and lemon scented eucalyptus essential oils. Obtain the Material Safety Data Sheet from your supplier to check the Flash Point of the oil you’re using. You should ideally keep the temperature of your soap below this value so scent does not unnecessarily flash off from the soap whilst being combined. 

As a general rule, I believe it’s safe to use up to 4% essential oil (eg 40ml) per 1000g of fat, but generally I use a 2% ratio. Scent can diminish over time, which is why a higher percentage may be desirable to use. Once soap is cured it can be wrapped in paper or material to help retain scent for a longer period. 

It’s important to do research to ensure the essential oil you want to use is safe for soap making.

Natural Colour & Texture

I like to use dried used coffee grounds to add colour and texture to my hand soaps. We use a coffee plunger at home and I simply tip out the used contents onto a plate and leave them out to dehydrate. Once dry, store in a jar for future soap making use. You can also ask your local cafe for their used grounds. 

Clays, dried herbs and spices can also be used, however I have not personally had much experience in using them yet. I have however used pink and green clay with great results. Some colours may change with curing.

My rule of thumb is to use 1 teaspoon of colourant, such as clay, per 500 grams of fat and up to 1 tablespoon of coffee grounds per 500 grams of fat. 




Safety Gear

The most dangerous aspect of making soap has to do with the lye solution. When mixing sodium hydroxide into water to create the lye the chemical reaction creates heat, releases fumes and produces a caustic solution. 

It’s important to make sure no children or pets can access the lye, a bund is used as a safety measure for spills (eg place container in a plastic tub), you’re in a well ventilated area for fume dispersion (eg near an open window), a mask is used to avoid breathing in fumes, goggles, protective clothing and gloves are worn to protect against splatters or spills. 

  • Goggles to protect your eyes
  • Rubber gloves
  • Long sleeve top, trousers, enclosed shoes
  • Face mask/cover (to avoid lye fumes – optional) – I use a wide large headband that I pull over my nose and mouth and keep my head away from the fumes
  • Vinegar for neutralising lye if there’s a spill

General Equipment

Main soap ingredients (fat, water, sodium hydroxide) should always be measured by weight via a digital scale. I’ve personally obtained my soap making equipment from secondhand op shops (besides my scale). I recommend using stainless steel mixing bowls and utensils. However you can also use enamel (with no chips), heat resistant glass, number 5 Polypropylene plastic. Don’t use: aluminium, tin, copper as they can react with the lye.

  • Digital scale
  • Stick blender – either stainless steel or plastic
  • Heating element to melt solid fats if applicable (eg stove top) 
  • Cutting board and cutter
  • Drying rack
  • Thermometer – I use an infared point and shoot thermometer that we bought to check the temperature of our pizza oven. 
  • pH test strips (optional)

Soap Making Equipment

  • Slops bucket (aka wash bucket) to put used equipment into
  • High sided container to weigh oil into (and mix soap)
  • Utensil to remove solid oil/butter from storage container (if applicable)
  • Container to weigh sodium hydroxide into (can be eliminated if you carefully weigh sodium hydroxide directly into water)
  • Utensil to remove sodium hydroxide from the storage container
  • Container to weigh water into (and then mix sodium hydroxide into, which gets very hot when reaction occurs)
  • Long handled utensil for mixing lye solution (lye = sodium hydroxide and water solution)
  • Utensil for colour or texture additives (if using)
  • Utensil for measuring essential oil (if using)
  • Utensil for spooning out soap into mould (if applicable)
  • Spatula for removing mixed soap from container and edges
  • Soap mould


You can use just about anything that holds a shape for soap making – including milk cartons. My personal favourite is using silicon moulds as they don’t require any lining and are easy to remove soap from. I recommend using a loaf shape mould for beginner soap making.

Depending on the mould you use you may have to line it with baking paper or a reusable silicone sheet so you can remove it when set. 

You can use the following formula to determine how much soap a mould will hold: Length x Width x Height = soap amount in grams.




It’s really important to recipe check any soap making recipes before making to ensure the sodium hydroxide ratio is correct for the oil/s used. I was alerted to a typing error I had made in one of the below recipes (which I’ve now edited). I don’t even know how I made the error, but it was a great lesson on the importance of recipe checking. I use www.soapcalc.net to check all recipes before making. 

Bar Soap Goals

  • Hard bar of soap
  • Palm oil free
  • Simple ingredients
  • Natural Additives
  • I don’t care if it looks pretty – I just want it to work well

Laundry and Dish Soap

This 1% Superfatted Coconut Oil Soap is designed to be an efficient cleaner with very little additional fat, other than to ensure all the lye has been used up in the recipe for safe use. I don’t add any colour and often no scent either. 

I originally found this recipe and the below hand soap recipe on the Mommypotamus blog.

  • 500g Refined Coconut Oil (24C/76F)
  • 190g Distilled or Demineralised Water
  • 90.71g Sodium Hydroxide
  • 15g (~1 tablespoon) Essential Oil (optional)

Hand Soap

This 20% Superfatted Coconut Oil Soap is versatile enough to be used for hands and body, although my personal preference is to use it as a hand soap. It produces an extremely solid bar of soap which is very cleansing, making it great for dirty hands and bodies. It can be used effectively in hard water and is a great marine soap, producing a good lather. Some people with sensitive skin can find 100% coconut oil soap too cleansing and drying, in which case I would swap this recipe for the one below. 

I always add a colour or texture so this soap is distinguishable from the Laundry and Dish Soap. 

  • 500g Refined Coconut Oil (24C/76F)
  • 190g Distilled or Demineralised Water
  • 73.3g Sodium Hydroxide
  • 15g (~1 tablespoon) Essential Oil (optional) – my favourite is Eucalyptus Lemon Oil (INCI: Eucalyptus citriodora)
  • 1 tablespoon used coffee grounds (optional)

Body and Hair Soap

I’m still in the process of formulating and testing hair and body soaps to see which one I like best. I want something that’s a little more nourishing than pure coconut oil soap. 

Here’s my current favourite: 

Coconut, Olive and Shea Soap 8% Superfatted

  • 250g Refined Coconut Oil (24C/76F)
  • 125g Olive Oil
  • 125g Shea Butter
  • 190g Distilled or Demineralised Water
  • 72.4g Sodium Hydroxide
  • 15g (~1 tablespoon) Essential Oil (optional) – my favourites are Lavender or Rosemary
  • 1 teaspoon coloured clay




  1. Set up your workstation, including pre-prepared moulds, so everything is laid out and easily accessible.
  2. Put on safety gear.
  3. Weigh out water into a heat proof container, within a bunded area.
  4. Weigh out sodium hydroxide into a separate bowl (or you can carefully weigh it directly into the water, stopping to stir occasionally).
  5. Add the sodium hydroxide to the water in a ventilated area (ALWAYS ADD LYE TO WATER – not the other way round) and mix to combine. This produces a chemical reaction that produces fumes and heat. Avoid breathing the fumes. Let the mixture stand (mixing occasionally) until it becomes clear and cools to ~ 40C (or lower than the flash point of the essential oil being used, if applicable). Ensure all sodium hydroxide crystals are dissolved before using.
  6. Weigh out your oils/butters and use low heat until just melted (if necessary).
  7. Add your mixer (stick blender – not turned on) into the middle of container with oil/s and pour the lye mixture into the oil using the mixer to guide the lye solution into the oil. 
  8. Mix briefly to combine while mixer is still turned off. 
  9. Turn on blender to mix, ensuring it stays below the solution to avoid splashing and incorporating air, and blend using a figure 8 motion until you reach a light trace (this is when the fat and lye are saponified). Light trace is when the mixture starts to thicken and leaves a trace when you take the turned off blender out of the mixture. You can use a spatula to scrape the edges and ensure all oil and lye are combined. 
  10. While your blender is off, add any additional ingredients, such as coffee grounds or essential oils and stir briefly (with turned off blender) to combine. 
  11. Turn on blender to incorporate additional ingredients. 
  12. Pour or scoop mixture into moulds and store somewhere safe while it sets. Safe = away from animals/humans – make sure it can not be knocked over or mistaken for food. An esky or cupboard can be suitable places. I personally use an esky as it contains the strong scent (if using essential oils) and keeps the temperature consistent while soap continues to react. 

After you pour your soap into your moulds it will continue to heat up for a while. Leave it for 12-24 hours to fully set (like a solid block of cheese) – there should be no heat coming from it when you go to cut it. 




As you’re making your soap, continue to add used items to your wash bucket. 

If you want to wash up straight away: Once you’ve poured your soap into the moulds you can attend to the ‘dishes’. Rinse your gloves if you have any soap on them. Keep your gloves on and add some vinegar to the wash bucket – concentrating particularly where the lye, lye solution and left over soap mixture are. Fill the wash bucket with warm/hot water and leave to soak for a few minutes. Empty the water and continue to wash equipment with your gloves on. 

OR let soap set and then wash up (my preferred method): After making soap, simply leave the used equipment to sit for a day or two and wash the set soap off the equipment. Use gloves. Soak and rinse equipment before washing. 

IF you intend to use the equipment for food preparation after making soap then it’s recommended to wash equipment a second time. I personally keep my soap making gear exclusively for soap, but some people don’t worry. You’ll have to do your own research and use your own intuition to know what’s right for you. Some people oppose using soap making gear for food preparation.




Use gloves when you take soap out of the mould as a precautionary measure. Remove soap from the mould and cut it before placing it on a drying rack to cure. If you use small individual silicon moulds, you can remove and place straight on the drying rack. 

Leave your soap to cure for 2+ weeks to allow excess water to evaporate, which makes the soap more solid and hard. This prevents soggy soap and also ensures it’s safe to use with no unreacted lye solution. 

I personally check my soaps pH before using by adding a little distilled water onto the soaps surface, agitating and then testing with a pH strip. My soap has always had a pH of around 9. I wouldn’t use a soap with a pH higher than 10, I’d keep it to rebatch (once I know how), or allow it to cure for longer and re-test. 

You can also periodically weigh your curing soaps to determine when bars stop changing weight (evaporating water).

I’ve found the scent of my soaps fade and evaporate over time, which is why I’ll use a high amount of essential oils if it’s a soap I know I’ll be keeping for a while and want to continue to smell nice. 

You can wrap soaps in paper offcuts or material to help maintain the scent. It’s important to ensure all water has evaporated before wrapping, otherwise mould can form.

When using bar soap you want to allow it to dry between uses so it doesn’t sit in a pool of water. Use a soap dish, hang from a rope or place soap inside a vegetable bag (like an onion bag) and hang.

I like to keep soap slithers in my car and bag for when I may need soap while I’m out. You can simply shave soap slithers off your bar soap with a vegetable peeler and store in a container. 




  • When I first started to make coconut oil soap I didn’t pay much attention to the temperature before mixing the fat and alkali together. I now allow the lye to cool to around 40C and have found saponification occurs much slower than when I’d mix the solution at a hotter temperature. I think keeping the temperature cooler allows for easier incorporation of additional ingredients. 
  • I’ve had great scent retention using Eucalyptus Lemon Oil (Eucalyptus citriodora), but have had the opposite experience when using plain Eucalyptus Oil. 
  • I made 20% superfatted coconut oil soap with coffee grounds and Tea Tree Oil in January 2020 and I’m not too sure that I like the smell of tea tree in the finished soap. I reckon I’ll stick to Eucalyptus Lemon Oil in the future. 




If you live in Perth and are more of a hands on learner, I would love to organise a soap making date.

Make and take a 750g block of soap of your choice (hand, body or laundry). Please check out the Services tab for more details, or upcoming events below. 




pH Reference

  • Sodium Hydroxide = pH 13-14
  • Soap = pH 8-10
  • Coconut Oil = ~pH 6 (from my personal test)
  • Our skin’s acid mantle = ~pH 5.5
  • Distilled White Vinegar = ~pH 2.4

Where I buy my soap making ingredients

  • Demineralised water (5 litre refillable container) = Big Bubble in Midvale Western Australia
  • Refined coconut oil (5 litre container) = Range Products in Welshpool Western Australia
  • Sodium hydroxide (2kg caustic soda) = Range Products in Welshpool Western Australia
  • Essential oils for soap = Range Products in Welshpool Western Australia
  • Coloured clays = Range Products in Welshpool Western Australia
  • www.rangeproducts.com.au
  • bigbubblemidland.com.au 

Books I like

Look in your Local Library for good soap making books. I always choose books that use natural additives. 

  • Aromatherapy Soap Making by Elizabeth M Wright. 2nd Edition. How to make your own luxury aromatherapy soaps
  • Smart Soapmaking by Anne L Watson. The simple guide to making soap quickly, safely and reliably OR how to make luxurious soaps for family, friends and yourself. Version 1.2
  • Scientific Soapmaking by Kevin M Dunn. The chemistry of the cold process. Revision 1.67
  • Handmade Soap Book by Melinda Cross. Easy soapmaking with natural ingredients. Updated second edition. (I got this from my local library)


Soap Calculator


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