Reconstruction techniques at Pompeii

One aspect that every Pompeian scholar is bound to come up against during the course of their research is the question of what is and isn't reconstructed at Pompeii. In the course of my own work I've examined walls and doorways time and again with this in mind. Now I'd like to open it up to other researchers to kindly point out some details that can be put together as recognised patterns of reconstruction that are otherwise unrecorded in the excavation reports, etc. Please post a reply if you can help with this!

Mortar - what is ancient and what is modern?
This is a big question because so much relies up on viewing a mortar up close. Occasionally it's possible to know what is a modern repair like repointing (to keep the opus incertum stones from falling apart and allowing the wall to collapse, etc), but does anyone have other markers to point out?

Blocked doorways: Blocked in antiquity or in modern times (and why)?
20th century site workers (muratore) developed a method of filling in doorways but leaving gaps at each side of the doorway to show that it was a modern fill. Of course, the largest clue lies in the modern mortar, but does anyone have further thoughts on this and/or why the muratore thought this was necessary?

Earthquake damage to walls in AD 63: How to know?
John Dobbins and the Pompeii Forum Project have carried out some great work on noting wall failure patterns and the subsequent repairs. But does anyone else have some tips?