Soft or sticky soap: causes and how to solve the problem

TL;DR: Soft soap = too much unsaturated oils, too much water, low NaOH, or summer temperatures. Solution: increase coconut oil, decrease water, add sodium lactate. Normal CP soap can be cut after 48 hrs, Castile soap needs 3-5 days.

Freshly removed soap is always softer than the finished piece after maturation - this is normal. The problem arises when the soap is noticeably soft or sticky even after 24-48 hours in the mold, difficult to cut, or after 4 weeks of aging still does not seem like a finished solid piece.

The causes are several and differ in their solutions.

Normal vs. problematic softness

Normal: Fresh CP soap (0-48 h) is softer than plasticine. It may deform slightly when removed from the mould. Can be cut after 24-48 h.

Borderline: The soap can be cut after 48 hours but is still sticky or stretchy like a rubber band. After 4 weeks of curing, it will firm up.

Problematic: The soap cannot be cut even after 48-72 h (it deforms). After 2 weeks it is still soft or sticky. After 4 weeks, it does not harden to normal stiff soap.

Cause 1: Too many unsaturated oils

Fatty acids are divided into saturated (solid at room temperature - palmitic, stearic, lauric) and unsaturated (liquid - oleic, linoleic, linolenic).

Soaps made from oils high in saturated fatty acids set quickly and are hard. Soaps with a predominance of unsaturated fats are softer.

Problematic oils for hardness: Olive, sunflower, rapeseed, linseed, hemp, almond - high content of oleic or linoleic acid → soft soap.

Oils contributing to hardness: Coconut, palm kernel (lauric acid), palm (palmitic acid), tallow/lard (stearic + palmitic), wax.

Solutions: Check the SoapCalc "hardness“ score for your recipe. Recommended score: 29-54. If it's below 29, increase the coconut oil or add a bit of stearic acid.

Castile soap (100% olive oil) is extreme - it solidifies very slowly. Standard Castilian soap cannot be cut within 72-96 hrs and only fully solidifies after 6-12 months of aging. This is its nature, not a defect.

Cause 2: Excessive water

More water = longer evaporation = slower solidification = longer stay in shape.

Standard amount of water: 33-38% of the total weight of oils.

If you use 40% or more, the soap will stay soft longer.

Solutions:

• Reduce the amount of water to 33% (water discount).
• Add sodium lactate (1 tsp per 500 g of oils) to the leaching solution - it will speed up solidification.
• Or: add powdered milk or sodium chloride (salt) - these additives also speed up setting.

Warning: Water discount speeds up the trace - for swirls or complex designs it shortens the working window.

Cause 3: Insufficient amount of lye (miscalculation)

If too little NaOH has been used in the recipe (too much superfat, calculation error or wrong SAP number), some of the oils will remain unsaponified. Unsaponified oil is not solid - the soap will be soft or oily.

How to tell: The soap has a greasy feeling on the surface or leaves a greasy imprint. May have transparent greasy stains.

Solutions:

• Check the calculation in the calculator - is the superfat set to 5-8%? Higher (10-15%) = softer soap.
• Verify that you have used the correct form of lye (NaOH vs. KOH) and the correct SAP number for each oil.
• If you have used too much oil (weighing wrong) - the soap is overfilled.

Cause 4: Too much superfat in the recipe

Superfat (SF) 5-8% is the standard - a healthy overfatting for a conditioning effect. But a SF of 15-20% means that 15-20% of the oils remain unsaponified, which will soften the soap considerably.

When higher SF is worthwhile: Soap for personal use only, not for sale. Castile soap or hair soaps with SF 10%.

When it's a problem: SF above 12% combined with a high proportion of unsaturated oils = very soft soap with a short shelf life (oils oxidize faster = DOS).

Cause 5: Overheating (overheated gel)

Paradoxně, přehřátí může způsobit i anomální měkkost. Pokud mýdlo v gel fázi dosáhne příliš vysoké teploty (>75–80 °C), může dojít k „přetavení“ mýdlové struktury — oddělení vody nebo deformaci krystalické mříže stearátů.

Symptoms of overheating: After removal from the mould, the soap has liquid or sour liquid on the surface (lye pocket) or has a glassy, transparent appearance only in part of the mould.

Solutions: Put the overheated piece of soap back for 24 h - if the lye pocket is tiny, the saponification will complete. If it is large - HP rescue.

Cause 6: Summer production or hot room

Soap sets more slowly in summer or in a warm room above 25 °C. Temperature slows down the crystallisation of stearates.

Solutions: Plan to make in the morning or evening in summer when the room is cooler. Put the moulds in a cool room or in the fridge for 30-60 minutes after filling (CPOP - cold process oven process in reverse: cold mould instead of warm).

Practical procedure for soft soap

1. Fresh (0-48 h): Keep in shape. Don't panic. Leave the Castile soap for 3-5 days.
2. Still sticky after 48 hours: Check the recipe and calculations in the calculator.
3. Still soft after 1 week: Consider HP rescue process or accept that the soap needs longer maturation.
4. After 4 weeks still not quite stiff: Check that the NaOH calculation is not too high or has been incorrectly calculated.

Solidification accelerators (summary)

Frequently asked questions

How long does it take for the soft soap to strengthen? Normal recipe: 24-48 h. Castile or very soft: 3-5 days or longer.

Can I reduce the freezing time by using a freezer? Yes, a refrigerator or freezer will slow down the gel phase and speed up the physical solidification, but the chemical saponification will slow down. Suitable for 30-60 minutes after filling.

What is superfat and how to reduce it? Superfat is a deliberate overfatting - % of oils that do not saponify. Standard: 5-8%. Reduce to 5% in the calculator for harder soaps.

Is the SoapCalc hardness score important? Yes, it's a good indicator. A score of 29-54 is fine, below 29 = soft soap.

Can I add stearic acid to any recipe? Yes, 5% stearic acid will firm it up considerably. It increases hardness but reduces conditioning.

What is water discount and will it affect the design? Water discount = less water (30-33% instead of 38%). Speeds up trace - for swirls this can complicate design.

See also:

• Troubleshooting encyclopedia
• Soap calculator - how to set the hardness score
• Oil encyclopedia - fatty acids and their effect on hardness
• Castile soap - why it solidifies so slowly