18.  What kind of testing do you
      recommend for stucco moisture

I prefer exterior moisture probes.  I use a proti-meter.  It has 1/8 inch probes…approx…I do not consider it or call it destructive testing.  Destructive testing is for me….cutting away a piece of the stucco to observe the substrate.  I would never do destructive testing without a stucco person present to make repairs and only after the homeowner signs permission…..and not before my moisture probe revealed serious deterioration.  Even then I hardly ever do it.
I call the moisture probe testing….intrusive testing …not destructive testing…and I believe that it will not harm or cause harm to the envelope if it is properly sealed.  At times people will say….but it will make a hole in the tarpaper and that will let water in the house.  The reality is that there is a hole in the tarpaper every 6 inches on every stud on the entire house….a few more small holes properly sealed will not matter….and the information that it will reveal is well worth it.  I always seal the hole first with a good elastomeric acrylic latex caulking of the 50 year guarantee variety…using a very small tip…and with warm caulking….this is important.  If the viscosity of the caulking is too thick then it will not easily flow into the hole all the way…and it will just plug the surface…which might be enough…but not really a complete fix.  Put the tip into the drill hole after testing and squeeze the warm sealant into the hole…until pressure builds up….if you have not drilled through the plywood then you will fill the hole….then release the pressure button so that it doesn’t squirt all around…at times it will actually go behind the tarpaper and come out the other hole an inch away.   If not repeat the process on the second hole.  Leave just a bit of caulking standing proud of the hole…so you can wipe it onto the edges with your clean finger.  Then dob just a bit on top to make it flush.  Of course try to use a caulking that is closest to the correct colour…not clear.  If the stucco can be chipped off…break a tiny piece off and stick it on top of the caulking to conceal the repair.
How do you do the drilling?
I use an 18 volt cordless drill with a 3/16 inch masonary bit…in good shape.  While drilling< I pay attention to the bit…..the reaction of the bit to the wood tells you a lot about the substrate.  If it just goes right through then you probably have a weakened substrate….is it does you cant test…so drill again a few inches over….but more carefully…observe the wood dust and chips that come out…what colour are they….how strong are they….you can usually feel the drill thump through the stucco and onto the sheeting….allowing a few revolutions to get through the tarpaper or housewrap….now repeat beside the test hole…..When you test…be sure your probes do not touch the side of the stucco…..if the stucco is wet it will squew the readings…move them around a bit and observe the movement of the readings.  Record your reading on a hand drawn elevation drawing that you can use for your report. 
Where do you test?
I usually test the weather wall…under the corner of windows….about 6 inches down…test under balcony railing about 6 inches down…test under exterior compression joint on the exterior corner….about 6 inches down.  Test under any black or brown stain …trying to determine the entry point…because it can travel behind the tarpaper for a long way before you see it coming out.  Stucco rarely leaks in the field of the wall…..it is around penetrations…and it rarely has ingress on the weather shadow of the wall.  Therefore determine which wall has the worst weather impact….usually the east wall…..but on the slopes of the mountains can be north as well….or any wall that the wind slams the rain against it….and there are not good overhangs.