Your advice on carbided tipped chisels, please

[Craig Vachon <vachon.craig@xxxxxxxxxxxx>]

Team:  I've only been carving stone for two years.  I
have much to learn.

A year ago, I moved to Tokyo Japan and started carving
gray granite.  My first piece (a 100 kg. relief of my
wife's behind) was very successful and satisfying.  My
second piece (her torso- 200 kg.) is killing me.  I
primarily use a 4' grinder and hand tools.  I am having
trouble keeping carbide tipped flat chisels for more
than 2-5 hours of carving.  They keep
breaking/shattering at the tip.  This is costing me a
fortune...

Can anyone advise me on how to keep these expensive
tools from breaking?  (I only strike the chisel with the
hammer once for every ten seconds - and always move the
chisel from the last place struck...)

What am I doing wrong?  (probably a great deal - but the
man that sells them to me has not been able to help...
Then again, I think I am putting his children through
college in the States...)

Each chisel cost about JPY4500 or US$40.  Are they less
expensive elsewhere?

Any and all assistance is appreciated.  craig

PS.  My wife demands that I inform you all that the
stone carving weighs 100kg - not her butt.  Thank you
for the clarification dear...