How to document masonry decay between condition reviews

Most condition surveys happen on a cycle: every five years, sometimes longer if a monument isn't flagged as at-risk. Between those formal reviews, the person who notices the new spall on a cornice or the widening crack above a window arch is usually whoever's on site for something else entirely, a maintenance visit, a planning consultation, a routine walk-round. What they do with that observation matters more than people tend to admit.

The standard answer is a photo log. Someone takes a shot of the decayed area, notes the date, maybe scribbles a grid reference or "north elevation, third bay" in a spreadsheet. It's better than nothing, and for isolated incidents like a stone falling off a parapet, it's genuinely all you need. The trouble starts when you try to use that photo log to answer a harder question: is this decay getting worse, and how fast?

Why photo comparisons break down

A photo taken in March with low raking light will show surface texture a June photo taken at midday simply won't. Shift the camera position six inches, swap the lens, or let five years pass between someone remembering to repeat the same angle, and you've got two images that aren't really comparable. You can eyeball them side by side and form an impression, but an impression isn't a record. If a question ever comes up about whether a repair campaign was justified, or whether decay accelerated after a drainage fault, "it looked worse to me" doesn't hold up well in a report.

The usual workarounds help a bit. Crack monitors (the little tell-tale gauges glued across a fissure) give you a number for movement at a specific point. A fixed grid taped to the wall gives you scale in a photo. A condition rating scale, the kind most authorities already use, at least forces some consistency in how "moderate" decay is described versus "severe." None of these solve the underlying problem, though: they're all point measurements or subjective categories layered onto a 2D image of a 3D surface that's eroding in three dimensions.

What a measurable baseline gives you

The gap photo logs can't close is volume. A condition rating might tell you a cornice has gone from "slight" to "moderate" erosion, but it won't tell you how many millimetres of stone have actually been lost, or whether the loss is concentrated at one bedding joint versus spread across the whole run. That's the kind of question that only a proper geometric baseline answers, something you can measure against rather than compare by eye.

A photogrammetric 3D model earns its place alongside the photo log rather than replacing it day to day. You need one at the points that matter: when the monument is first brought under formal management, and again at each condition review, so the review itself has something more rigorous to work from than last time's notes and this time's photos. Heritage Documentation flies a drone or crewed-aircraft survey over the monument and returns exactly that, a baseline model built from sub-10cm RGB imagery, repeated at each review so you're measuring the same surface against itself rather than guessing from two unmatched photographs.

In between, the photo log and the crack monitor still do their job. They're your early-warning system, the thing that tells you a review needs to happen sooner than scheduled. What changes is what happens at the review itself: instead of starting from a stack of loosely dated photos, you start from a model you can overlay on the last one and measure the difference directly.

If your next review is approaching and you want a baseline that holds up better than a photo folder, that's the gap Heritage Documentation is built to close.