Sodium hydroxide becomes hard and very difficult to dissolve in water.
Add some more water and let it dissolve. This makes the JWA easy to use.  

Hello, For future reference I would not recommend your readers, students, gardeners, use sodium hydroxide when making JWA even if potassium hydroxide is NOT available.
I believe I achieved a good viscosity however it took approximately 5 hours of mixing with a drill over 3 days and using additional 100 litres of water.
Thank you  

Potassium = Bronners liquid soap
Sodium = Bronners bar soap

Both dilute same in water which you have to do before applying to plants so makes little difference?

You are not consuming it, so it matters little, use what is available,
and/or cheaper?

I don't really know, hard to find ingredients in stores here in US, have to look up drain cleaner ingredients online before buying from Home Depot. I used a potassium hydroxide 45% / water 55% drain cleaner that worked, but I question the water?