The preservative versus no preservative war isn't ever going to be won by either side. Zany doesn't use it at all, as she has mentioned here.
I don't use preservative in the paste. I do use preservative in the diluted soap. I can trot out all the reasons why I use it, but I'm not. Suffice to say I use it.
I have no idea what the downsides are of using LGP at 3%. I would be uncomfortable with it. It's a formaldehyde releaser which squicks some people out, although fruits such as apples release formaldehyde in comparable amounts to LGP when used at recommended rates. We eat apples, rather than wash our hands with apples, but somehow LGP is evil and apples aren't. But LGP at 3% ... that's a lot. I can't advise.
Dumfrey suggests mixing this soap with plain soap to dilute the LGP. That's a theoretically sound plan, but you'll have to make more than "a few batches" to dilute the LGP to 0.5%.
You'll end up with a volume of diluted soap that's six times larger than you currently have. That's a
lot of liquid soap. You'll have to decide if you can get that much soap used up in a reasonable amount of time. Are you only using it for handwashing in your household? Can you give it away? Are there other uses for this soap?
I normally make one batch of paste with 300 g of fats and the diluted soap from that one batch lasts me better part of a year if used mostly for regular househould hand washing. (I also use it for my hobby of wet felting and it gets used up faster when I felt a lot). But a six-times larger batch of LS would last me for years even with my felting ... to the point where the soap would probably go rancid first.
I read it horribly wrong! 0.1 - .05%
In the interests of ensuring other people aren't misinformed, the numbers are 0.1 -
0.5%. That's 1 to 5 grams of Liquid Germall Plus per 1000 grams of finished product.
I recommend the upper amount of 0.5% for hobby/home crafters who aren't able to do formal challenge testing.