Weekly DIY

Heavy-Duty Liquid Soap

Explore potassium hydroxide to create a simple yet powerful liquid soap that cuts through greasy kitchens, dirty sinks, tiled surfaces and everyday grime.

4–7 hours, plus 24–72 hours to settle

Intermediate - Advanced

Concerns

Kitchen Grease • Dirty Sinks • Tiles • Dried Spills • Everyday Grime

Benefits

Cuts Grease • Rich Lather • Lifts Everyday Grime

Format

Liquid Soap / Cream Cleaner

Shelf life

Use within 3 months once diluted. Store tightly closed and discard if the colour, smell or texture changes.

What You'll Need

Potassium Hydroxide
69 grams
Powerhouse ingredient that transforms oil into a strong liquid soap.

Coconut Oil
269 grams
One of soapmaking’s strongest cleansing oils, creating abundant lather and serious grease-cutting power once transformed into soap.

Calcium Carbonate
100 grams per 100g soap concentrate
A naturally occurring mineral powder that adds the familiar scrub of a cream cleaner, helping shift dried spills, stubborn marks and built-up grime.

How to Make

Before You Start:

You'll need the following safety equipment:

Splash goggles
Chemical-resistant gloves
Long sleeves
Closed shoes

In case of contact: Immediately rinse affected skin with plenty of running water. If KOH enters the eyes, rinse continuously and seek urgent medical attention. Do not attempt to neutralise skin or eyes using vinegar or another acid.

Making the Potassium Soap Concentrate

1. Prepare your workspace:

Work in a well-ventilated area away from children, pets, food and unnecessary clutter.
Put on your gloves, splash goggles, long sleeves and closed shoes before opening the potassium hydroxide. Potassium hydroxide is strongly corrosive before it reacts and can cause serious skin and eye burns. Heat is also generated when it contacts water.

2. Prepare the potassium hydroxide solution

Weigh 161g distilled water into a sturdy, heat-resistant container (see below for which container).
Slowly add 69g potassium hydroxide to the water, stirring carefully until fully dissolved.
Always add the potassium hydroxide to the water - never pour water onto dry potassium hydroxide.
The solution will become extremely hot. Keep your face away from the container and do not breathe in vapour or mist.
Set it aside in a secure place and allow it to cool to approximately 40–50°C.

3. Prepare the coconut oil

Weigh 269g coconut oil into a stainless-steel pot or dedicated slow cooker.
Heat gently until completely melted, then allow it to settle at approximately 45–55°C.
The oil and KOH solution do not need to be exactly the same temperature, but both should be warm and safely manageable.

4. Combine and blend to trace

Slowly pour the KOH solution into the melted coconut oil.
Blend using short bursts with an immersion blender, alternating with gentle hand stirring.
Continue until the mixture reaches a stable, thick trace. It should resemble thick custard or pudding and should not immediately separate when left standing.
Trace means the oil and KOH solution have formed a stable emulsion. It does not yet guarantee that the soap has finished reacting.

5. Cover the pot and cook over low, gentle heat.
Use either:

a slow cooker on its lowest setting.
a stainless-steel pot inside a water bath.
very low controlled stovetop heat.

Do not allow it to boil.

Stir carefully every 15–30 minutes. The mixture may move through several appearances:

thick cream.
a grainy or mashed-potato texture.
a stiff, waxy paste.
a smoother, glossy or gel-like soap concentrate.

With 100% coconut oil, the concentrate may remain pale or opaque. It does not have to become completely transparent.
Continue cooking until:

no separate oil remains.
no watery KOH-rich pockets are visible.
no dry crystals remain.
the mixture forms one uniform soap concentrate.

This may take approximately 1–3 hours, depending on the equipment, batch size and temperature.

6. Test the concentrate

Remove approximately ½ teaspoon of soap concentrate and dissolve it in about 30 ml hot distilled water.

The sample may be clear, cloudy or milky. What matters most is that you do not see:

floating oil droplets.
a greasy film.
hard crystals.
obvious separation.

7. Cool and weigh

Remove the completed soap concentrate from the heat and allow it to cool.
Once cool, weigh the finished concentrate. Use this actual weight to calculate the dilution water.
The concentrate may become very firm as it cools. That is normal - it is concentrated potassium coconut soap, not yet the finished liquid cleaner.

Diluting the Soap Concentrate

1. Calculate the dilution water

Use:
1 part soap concentrate to 3 parts distilled water

For example:

100g soap concentrate - 300g distilled water
250g soap concentrate - 750g distilled water
500g soap concentrate - 1500g distilled water

2. Add the water

Using gloves, place the soap concentrate into a clean stainless-steel pot.
Add the measured distilled water and warm gently over low heat, keeping the pot covered to minimise evaporation.
Allow the concentrate to soften and dissolve, stirring occasionally.
Do not boil it, and avoid using an immersion blender once the diluted soap is hot, as this can create excessive foam and increase the risk of splashing.

3. Add the calcium carbonate

Once the soap concentrate has fully dissolved, remove the pot from the heat and allow the mixture to cool until warm rather than hot.
Gradually stir in calcium carbonate at a 4:1 ratio (and hydroxyethyl cellulose if using).

For example:
If you used 100g soap concentrate + 300g distilled water = 400g Diluted potassium soap
400g Diluted potassium soap + 100g Calcium carbonate = 500g Final batch
Add the powder slowly while stirring to avoid clumps. Continue mixing until the calcium carbonate is evenly dispersed and the cleaner has a smooth, creamy texture.

4. Allow it to settle
Transfer the cleaner into a suitable container, cover and leave it undisturbed for 24–72 hours.
During this time:

any remaining soap pieces should finish hydrating.
the final thickness will develop.
the calcium carbonate may reveal whether it stays suspended or begins settling.

Some cloudiness is normal, particularly with a 100% coconut-oil potassium soap.

How to Use

Guidance

Apply a small amount to a damp sponge or cleaning cloth, then work it over the surface to loosen grease, grime and dried-on residue. For tougher marks, leave it on for 1–2 minutes, scrub gently, then rinse or wipe away thoroughly with clean water.

Wear cleaning gloves during use, as this is a highly cleansing alkaline soap and may dry out the hands. Always patch test first. Avoid delicate finishes, aluminium, natural stone, unfinished wood, non-stick coatings and any surface that may be damaged by alkaline or abrasive cleaners.

Make It Yours

For More Body:
Add ½–1 teaspoon Hydroxyethyl Cellulose per 500g cleaner as per method above. Allow it to hydrate fully before judging the final texture.
For A Fresh Citrus Boost:
Add ½ teaspoon Sweet Orange Essential Oil per 500g cleaner for a brighter scent and extra support with oily, sticky grime.
For A Gentler Everyday Cleaner:
Remove the Calcium Carbonate for a smoother cleaner with less scrubbing power.
For A Gentler Liquid Body Soap:
Replace the household-cleaning formula with a more balanced blend of 50% sweet almond oil, 30% coconut oil and 20% castor oil.
For a 500g oil batch, use 250g sweet almond oil, 150g coconut oil, 100g castor oil, 100g pure potassium hydroxide and 190g distilled water - and removing the calcium carbonate. This version includes a 5% superfat for a softer, more conditioning cleanse.

Pro Tips & Storage

Can you add ingredients to make it gentler on hands?
Adding ingredients that hydrate the skin may leave a residue on surfaces cleaned. Dilute the soap further rather than adding skincare actives, and always wear cleaning gloves during use.
Why use potassium hydroxide instead of caustic soda?
Potassium hydroxide creates a softer, more water-soluble soap that can be diluted into a liquid cleaner. Caustic soda is generally used to make firm soap bars.
What containers should you avoid making the potassium soap in?

Do not make or mix potassium soap in:
- Aluminium, zinc, tin or galvanised metal - strong alkalis can attack these metals and may release hydrogen gas.
- Normal, thin glass jars- the KOH solution becomes extremely hot and sudden temperature changes can crack the glass.
- Styrofoam or thin disposable plastic - these may soften, warp or fail under the heat.
- PET plastic (marked recycling code 1)
- Damaged non-stick cookware.
- Ceramic containers with cracks, chips or damaged glaze.
- Any container that will later be used for food.
Use a dedicated stainless-steel vessel, or a sturdy container marked HDPE 2 or PP 5. For heating and cooking the soap paste, stainless steel is the best choice.
Does potassium soap need to cure for several weeks?
Not like a cold-process soap bar. Once the soap paste has been cooked until fully reacted, it can be diluted and left to settle for 24–72 hours before use.
Can I use this potassium soap as a body soap?
No. This particular formula uses 100% coconut oil with no superfat and is designed for household cleaning, making it much too cleansing for regular use on skin.
Potassium hydroxide can be used to create liquid body soap, but that requires a separately calculated formula with a gentler oil blend and suitable superfat.
Do I need to wear gloves when using it?
Yes. Even when properly saponified, this is a strong alkaline cleaning soap that can leave hands feeling very dry.

Essentially Natural Caustic Potash (Potassium hydroxide)

R 89.00

Credé Refined Coconut Oil - Odourless

R 75.00

Essentially Natural Calcium Carbonate

R 39.00

Aiden van Wyk

Aiden is an eccentric explorer of ideas, endlessly curious and always eager to share his discoveries. His mind is a maze of rabbit holes, each leading to new insights (and occasionally pure chaos). In all honesty - he's a little impulsive, he's easily distracted, delightfully scatterbrained, and unapologetically himself. But through every deep dive and misstep, his mission remains the same:

To make the world a teeny tiny little better, one lesson at a time :)