How to Dilute Castile Soap Paste into Liquid Soap

Diluting is the step that turns your concentrated castile soap paste into finished liquid soap. Get the water-to-paste ratio right and it dissolves cleanly into a smooth, professional soap; rush it and you get cloudy soap with undissolved lumps. Here is the method I use for large batches:

The method, step by step

1. Calculate your dilution. Use a dilution calculator — enter the soap weight and your desired concentration to get the water and additive measurements. (More on the calculator below.)
2. Add paste to hot water. Add the main portion of soap paste into boiling water.
3. Clean the container. Pour a little hot water from the main pot into the paste container, scrape the sides and base, cover, and let it sit about 15 minutes to loosen the residual paste.
4. Transfer the residue. Loosen the remaining paste from the container and add it to the main pot.
5. Allow initial dilution. Let the paste sit and dilute over a few hours.
6. Dilute the stubborn pieces. Strain out any floating soap pieces into a smaller pot, add a little hot water, apply brief heat for about 15 minutes to speed things up, then pour back into the main pot.
7. Final strain. Strain the finished liquid soap through a fine sieve or cheesecloth into a clean storage container.

Getting the ratio right — the calculator

The single biggest factor in a good result is the dilution ratio, and that is exactly what our free soap paste dilution calculator works out for you. You enter the weight of your paste and your target soap strength, and it tells you how much water to add — plus room to set optional additives like glycerin, preservative, or thickener. After diluting, you can enter the new weight and it tells you exactly how much more water is needed to finish. It takes the guesswork out completely.

Once diluted, if your soap comes out thinner than you would like, that is normal for castile — you can thicken it with HEC to a smooth, professional finish.