Optimize the join between new stucco and old?

Thanks for excellent information nicely presented. Just spent an hour browsing your site.

I'm more of a cabinet guy, but I rebuilt the 10 x 10 laundry wing on my small single-story SoCal home.  It's a wannabe craftsman kit home with redwood clapboard built in 1917, and received stucco in 1947.  Good materials, decently applied, 5/8" average thickness overall.  No signs of cracks or degradation from moisture.

I cut the old stucco with an abrasive blade on a circular saw.  One cut, nice & clean.  Now I'm ready to apply paper and pre-furred woven wire lath.   How do I optimize the join between new stucco and old? 

There's a vertical cut nice & smooth, showing base coast with embedded wire, and top coat.  The cut slices the tarpaper beneath, and just scores the outer skirt of the clapboard.  Then my new sheathing.  Maybe I could work heavy wire into the horizontal gaps between each clapboard, even epoxy them in, and tie them to the new lath?  Maybe I should chamfer the edge of nice clean cut so new stucco has a chance to fair in?  Basic integrity of the whole stucco web is my chief concern; appearance matters much less on this utility porch at the rear of the home.

Optimizing the join between new stucco and old

Here, a mixture of flex-con, an acrylic bonding admixture, and portland cement with no sand is painted on the join. The surface is left as rough as possible. This not only prevents edge cracking, it avoids a nasty hump.

A rough edge would bond better but this is will work even if you have a slick join.

I believe heavily in flex-con, but there are other acrylic bonding admixtures.

We mix pure flex-con (no water) portland cement (no sand) in a cup or something until it is a paste. Paint this on your join leaving the paste rough. You may want to wet the join first.

This will work 95%+ of the time

Thanks so much for visiting my site and for the great question.