When to replace the mast rather than repair it
 

I've pulled the spars off our Friendship Sloop for some needed rigging replacement and potential spar repair. That got me thinking about scarfing in new wood to replace rot, which got me to thinking-how long can one continue to add scarfs on a mast? Is it possible to start with a scarf at one end and continue to replace bad wood until youhave an entirely new mast? At what time does it make more sense to just buy a new piece and start over?

Just wondering. . .

Thanks,

Harvey