blueman wrote:
Our 100+ yr old plaster lathe walls from time to time develop hairline
cracks.

Googline, I see that some DIY articles recommend taping and others say
that for hairline cracks it is sufficient to dig it out and fill with
drywall or plaster patch.

Since taping takes more time and coats to feather out nicely, I would
like to know when (if ever) is it sufficient to just dig out the
crack and patch it without tape? (assuming that I want the crack not
to open up again)

Also, is it better to use plaster patching compound or drywall
compound? (the plaster patching compound drys much harder but is
therefore also harder to sand down)

None of the above.

Plaster shouldn't be painted for about a month, so don't using plaster
patching compounds unless they specify a much shorter time for
finishing. Better yet, don't use plaster patching compounds at all.

Digging out hairline cracks is a waste of time. You want that hairline
to disappear, making it larger is a strange way to go about doing it.
That advice comes from years gone by and is for larger cracks.

The best stuff to use is called Krack-Kote. It's fast to apply and
dries quickly, hardly _any_ buildup at all so there's no hump in the
wall like regular drywall tape and compound would give you, it's
available in regular paint stores and you can paint over it almost
immediately.

http://www.tuffkoteco.com/store/store.htm

I suggest you keep the door closed while you're working, emerge
periodically to yell and curse about what a _bitch_ fixing those cracks
is, leave stuff all over the room, and milk it for all it's worth.
Don't make it look too easy.

R