I have never had HP soap separate after molding, so I am wondering if you put it in the mold before saponification was complete. Once the oils are saponified, the soap shouldn't separate, I don't think. Unless you add something to it that tears it apart, like loads of lemon juice.
Before making another batch of HP soap, I would suggest reviewing this video to make sure you are completing all the necessary steps to get the soap to the point where it is ready to put into the mold:
The only thing I would add to the above, if you are unsure if saponification is complete, is to do the zap test at the 'Vaseline' stage. See how the soap looks in the video at about 5:12 (5 minutes, 12 seconds), that's when she says it is in the final stage of HP, often called the Vaseline stage. To do the zap test, first remove a tiny bit with a spoon (or other utensil) and let it COOL before doing a zap test. Wet your gloved hand and rub the cooled soap paste to create a bit of soapy lather, then touch that to your tongue. This is basically the same as zap testing a finished soap as described in our
SMF sticky, except it's done with the cooked paste before it has a chance to set up in the mold.
The other thing I would add to that video is that HP soap benefits from a longer cure, the same as CP soap.
