1. Impermeable finishes on walls that need to breathe
By a distance the most common problem on the island, and it is almost always self-inflicted during a previous renovation.
Traditional walls — stone, lime mortar, lime plaster — and cave walls surrounded by damp rock both work by letting moisture pass through the finish and evaporate. Replace that finish with cement render and acrylic paint and the moisture reaches a barrier it cannot cross. It collects, condenses, and pushes the surface off in sheets.
How to recognise it: paint or render lifting in sheets rather than fading; damp patches that return after redecoration; a white bloom of salts at the surface.
What actually fixes it: removing the impermeable layers back to substrate and rebuilding in lime, plus dealing with any water arriving from above. Another coat of something better repeats the failure. See cave house damp proofing and plastering.
2. Terrace waterproofing failing through movement
A terrace here takes direct sun all day and cools sharply overnight. That daily expansion and contraction is relentless, and it is what tears badly detailed systems apart — not water pressure.
How to recognise it: a leak in the room below after rain; cracking in a line across a tiled terrace; ponding water that does not drain.
Why it happened: falls formed in the tile bed rather than the screed; no separating layer between membrane and finish; missing movement joints; a rigidly grouted perimeter; an upstand too low for wind-driven rain.
What fixes it: the sequence, done properly. See waterproofing. Coating over a failed system with water still tracking underneath moves the leak rather than stopping it.
3. Salt corrosion of reinforcement and fixings
Chloride from salt-laden air penetrates concrete and depassivates the steel inside. Corroding steel expands to several times its original volume and pushes the cover off from the inside.
How to recognise it: spalled concrete with rust-stained bars showing, typically at balcony edges and soffits; rust stains running down whitewashed walls from a fixing above; seized window hardware; corroded balustrade base fixings.
Why it happened: insufficient cover, a permeable mix, and the wrong grade of stainless — or plain steel — at fixings.
What fixes it: proper concrete repair, breaking out well beyond the visible damage and fully behind the bar, not a cosmetic patch. And replacing fixings in A316. See salt-air corrosion protection.
4. Differential settlement in variable ground
Depth to competent material changes across a single Santorini plot, sometimes dramatically. A building founded partly on competent tuff and partly on loose pumice will settle unevenly.
How to recognise it: diagonal cracking radiating from the corners of door and window openings; doors and windows that bind on one side of a building; a crack that is wider at one end.
Why it happened: foundation design based on assumption rather than on a trial pit — frequently on "what the neighbour did".
What fixes it: an engineer's assessment first. The remedy depends on whether movement is historic and stable or progressive, and those are different situations with different answers. See volcanic soil foundations and structural cracks.
5. Drainage at capacity
A system sized for the original house, serving a property that has since been extended, converted and let to eight guests in August.
How to recognise it: recurring blockages in the same place; slow drainage that gets worse with occupancy; a cesspit needing emptying far more often than it used to; smells at peak use.
Why it happened: incremental extension without ever revisiting the system, and a use pattern nobody designed for.
What fixes it: capacity assessment against actual peak occupancy, a camera survey to find falls and collapses, and either upgrading the system or accepting a much shorter emptying interval. See drainage and septic.
Recurring blockages in the same place almost always mean inadequate fall or a partial collapse rather than what is being flushed.
6. The junction between old and new
Most Santorini buildings are two or three buildings joined together: a stone-and-vault original, a concrete addition from the 1970s or 1980s, and something lighter added later. They have different stiffness, different foundations and different thermal behaviour, and they were joined without provision for any of it.
How to recognise it: a straight vertical crack in exactly the same place after every redecoration; a line visible through the render across an elevation; damp concentrated along that line.
Why it happened: the two structures were butted together and rendered over.
What fixes it: deciding deliberately — tie them together so they act as one, having checked the old structure can take it, or separate them with a designed movement joint detailed to stay weathertight. Filling it again is money spent to repeat the problem. See extensions.
What they have in common
Five of the six were created by a previous intervention rather than by the building's age. Cement on a lime wall, a tiled terrace without movement joints, a fixing in the wrong material, an extension butted onto an original, a system extended without being resized.
The exception is settlement, which is a design failure at the start rather than a later one.
The practical implication is that the most valuable thing you can do to a Santorini building is understand it before improving it. Almost every expensive problem here started with someone making it better.
Questions people actually ask
My walls keep getting damp after redecorating. Why?
Almost certainly impermeable finishes on a wall that needs to dry outwards. Redecorating repeats it; the fix is stripping back and rebuilding in a breathable system.
Is a crack in my wall serious?
It depends on the pattern, the width and whether it is moving. Diagonal cracking at openings and separation at corners deserve an engineer. See structural cracks.
How do I know if my terrace waterproofing has failed?
Water in the room below after rain is the obvious sign. Ponding, cracked tiles in a line and a failed perimeter joint are the early ones.
Can these problems be fixed permanently?
Yes, when the cause is addressed rather than the symptom. What comes back is the repair that treated the symptom — filler in a moving crack, paint over trapped moisture, a coating over a failed membrane.
Which of these should I fix first?
Anything letting water into the building, then anything structural, then everything else. Water damage compounds faster than any other defect on this list.