I've got a 32 oz. can o' pitch from rio that I want in 5 parts.
Any sizeable hammer will do the job. Put the pitch inside a couple
plastic grocery bags, tie it up rather loosely but without open holes
and toss the bundle in a burlap sack that you don't mind trashing a
bit. Drop the lot in your freezer for a couple hours, or out on your
porch if you're in the snow-zone.
Now take your bundle and your hammer and head out to the driveway for
a little frustration relief. Don't get too enthusiastic though
because pitch powder isn't nearly as easy to deal with as pitch
chunks. Any basic scale will help you measure out the parts equally.
Another option, one I use, is a small axe such as a camping hatchet.
Cold pitch and an axe makes short work of such a job. I do this
inside a garbage bag --you've got your pitch, the axe and your arms in
the bag-- to keep pitch chips from flying all over the place. I know
it sounds crude but it's actually not bad at all if you're good with
an axe. If you really want to get elegant bring along a wood mallet.
Place the axe where you want to make a cut, whack it with the mallet,
voil=E0, nice chucks of pitch. Repeat as required.
As to the heating being a bad thing it's only doing harm to your
pitch if it's so hot it is bubbling, or worse yet, smoking. That's a
no-no for any pitch I've seen. A more moderate heat and a longer time
heating gives you warm, flowing pitch without doing it harm. I like a
heat gun on a low setting --surprising how useful heat guns really
are-- but if you like the woodsy smell in your kitchen, and possibly
the next few things you bake in the oven, then I suppose the oven
would do the job too.
When heating pitch I've found it best to think of it as a big heat
sponge: it soaks up heat over time but does not like being heated too
fast. In other words take your time. You'll get there in the end and
your pitch will appreciate the gentler treatment. Over-heated pitch
becomes brittle and unyielding once it's cooled again and that's not
very useful for most of the typical things you'd use pitch for.