If you'll read all the casing teks located under the grow/find Section of this site, I think you'll get a feel for it. You might also see if your local library has either "The Mushroom Cultivator" or "Growing Gourmet And Medicinal Mushrooms" by Paul Stamets. Both these books have very good chapters on casing.

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Your confusion is bourne of many different opinions and two quite seperate methods of casing.

You can "case" PF cakes by sticking some vermy on the top and bottom. Personally I never remove the sealing layer of verm from them in first place but prefer to wet it a bit instead. This is the first kind of casing and isn't "true" casing.

The second method involves you getting colonised substrate. This is a PF cake in your case but it could be some colonised grain or straw or whatever. You crumble or slice the cake up (or spread the grain around) to the depth of say a couple of inches and add 1/2-1" of casing material. This casing could be straight verm or more likely a mixture containing peat or soil. You then wait for the myclium to partially grow throught the casing layer and then initiate pinning.

This second, true casing method needs different humidity than PF cakes. Because "cased" (i.e. top and tail casing) PF cakes still have a lot of cake showing, they need near 100% humidity or they will dry out.

Rad

-have a pf cake fully colonized.
-crumble it.
-place the crumbled cake on the bottom of a foil pan or tupperware.
-then put a 1/2" moist vermi on top of it.
-store it in your terranium and it watch those shroomies grow.

as you can see it's very simple.