Hi Julie! Since you used the accurate amount of lye and oils, then the overall soap itself should be safe to use – however, the crumbling could mean that the bottom crumbly parts are lye heavy, while the top parts don’t have enough lye.

You have a few options:

1. Go ahead and give your soap the “zap test” – this is where you lightly touch your tongue to a soap that you’re unsure of and see what happens.
In this case, you would zap test a crumbly part, then you would zap test a part that looks okay.
If you feel a zappy jolt, like you licked a 9 volt battery (not that people commonly do that to compare!) :) – then it’s lye heavy.
If it just tastes gross, like you licked a bar of soap – then it should be fine to uses.
If the crumbly part “zaps” and the normal part doesn’t, then you need to rebatch your soap.

2. Let your soap cure for at least 4 to 6 weeks, then see if it zaps.

3. You could go ahead and rebatch this soap, and then you know for sure that the lye would be evenly distributed throughout and is safe to use.