What to expect
| Typical duration | Room 3–7 days · full house 2–5 weeks · lime needs curing time between coats |
|---|---|
| Cost band | Figures live in the cost index |
| Permit required | External finish controlled in designated settlements |
| Seasonal constraint | Lime work avoids frost and extreme heat |
The island's own binder
Santorini's volcanic earth is a natural pozzolan — it reacts with lime to produce a mortar that sets hard and works even in damp conditions. This is not folklore: Theran earth was quarried and exported in the nineteenth century as a hydraulic cement, and it was used in major waterworks of the period.
That history matters practically, not romantically. It explains why the cisterns hold, why traditional renders here are tougher than plain lime elsewhere, and why the right repair material for an old Santorini wall is a lime-pozzolan mix rather than either plain lime or cement.
Why cement render fails on old walls
Three separate mechanisms, all of them slow enough that the plasterer is long gone before the result appears.
- It is stronger than the wall. When the wall moves — and old walls move — the render does not. So the stone or the wall face fails instead of the mortar. The render survives; the wall does not.
- It is impermeable. Moisture in the wall reaches the back of the render, cannot evaporate through it, and detaches it. Where it is trapped over a winter it can carry salts to the interface and blow the bond entirely.
- It concentrates damage. A hard patch on a soft wall pushes movement and moisture to the edge of the patch, which is why a cement repair produces a ring of new damage around itself.
What a proper lime job involves
- Stripping back to sound substrate. On a wall with layers of cement and paint this is the majority of the labour, and it generates real quantities of waste to remove.
- Raking out and repointing defective joints in a compatible mortar before rendering.
- A scratch coat, a float coat and a finish coat, each allowed to cure. Curing is not drying — lime needs time and moisture, and rushing it produces a weak render that dusts.
- Protection from direct sun and wind during curing. On this island that is the harder half of the job in summer.
- Finishing in lime wash, or leaving as a lime finish, both of which stay vapour-open.
Modern substrates
Not everything should be lime. A modern block or concrete wall with a cavity or insulation behind it and no moisture path has no need to breathe, and a conventional cement-based or gypsum system will be cheaper, faster and entirely appropriate.
Where it gets interesting is the junction — extremely common here — between an original stone wall and a later concrete addition. Rendering across both with one material guarantees a crack along the line. Either the junction is detailed as a joint, or the two are rendered in compatible but separate systems. See extensions.
Questions people actually ask
Can you plaster over the existing cement render instead of removing it?
Technically possible, and it is usually the wrong answer. You would be adding a breathable layer on top of the impermeable one that is causing the problem. If the substrate has failed, it comes off.
How long does lime render take to cure?
Considerably longer than cement, with waiting time between coats. That is a programme fact rather than an inconvenience, and any schedule has to allow for it.
Is lime render more expensive than cement?
The material is inexpensive; the labour and the programme are longer. On an appropriate substrate it is the cheaper option over the building's life, because the alternative includes stripping failed work and repairing the wall beneath it.
Can lime render be used in a bathroom?
Yes, including in cave houses, and it frequently performs better than a sealed system because it manages moisture rather than trapping it. Splash zones are detailed with tile or a suitable finish; the rest of the room benefits from being vapour-open.
My plaster is dusty and comes off on my hand. What is that?
Usually lime that cured too fast, most often applied in heat or wind without protection. It can sometimes be consolidated, but frequently the coat needs replacing — and the reason it happened needs fixing, or it will happen again.