Having run out of homemade laundry liquid, I needed to make some pronto. I used to use half a bar of grated soap, then I found soap flakes which made the process easier. Unfortunately, it would appear that the main producer of soap flakes have now stopped making them. Instead they produce liquid soap for laundry, at a slightly higher price.
Off I went into the kitchen, started as normal. Obviously I didn't need to dissolve the soap flakes to begin with so just put 1 cup of liquid soap into 1 litre of water and stirred to mix. Then I added in my washing soda and stirred.
Straight away it was obvious something was different. Normally, when adding the washing soda, it quickly thickens when stirring, this just stayed the same. I felt it and it was very waterery and runny, not how it would normally feel, which is slimy.
I didn't add my usual 3 litres of water to make a product that would normally fill 2 x 4 pint milk cartons. It just didn't feel right so I poured it into one 4 pint container and topped up, so maybe 1 1/2 litres of cold water. The next day, it is the same, very runny, not slightly gloopy like it should be.
Guess then, that there is a big difference. On their own (i.e. not used to make into frugal laundry liquid), a box of flakes would give up to 10 washes as opposed to the liquid version that gives 15 (for a higher price).
However, it is now clear that the liquid soap flakes cannot successfully be made into a frugal laundry liquid, unless a very large amount of it is used. Even then, I am not sure it would work as it appears to be made differently. If anyone knows differently please let me know.
I did find online here someone asking a similar thing with an answer from the producers themselves:
You live and learn all the time!