Old houses in the eastern Algarve were built from stone, rubble or rammed earth and then coated in lime. The coating isn’t only decoration. It lets the walls breathe out moisture, and the trouble starts when someone covers it with cement render and plastic paint, because the water then has nowhere to go. If you are viewing a village house or a townhouse in Tavira, the state of the render will tell you more about the building than the brochure does. A sensible first question for the estate agents in Tavira handling the sale is whether the walls have been re-rendered in the last twenty years, and with what.
Why lime and cement fall out
Lime is soft, porous and a little forgiving. Cement is hard and nearly sealed. Put the second on top of the first and moisture that would normally pass through the wall and evaporate gets stuck behind the cement. It collects, creeps upwards, and eventually comes out somewhere else: blistered paint, powdery white salts, a damp smell in the back room that nobody can explain. The usual fix is to hack the cement off and start again in lime, which takes time and a plasterer who understands the material. Neither comes cheap.
Salt makes it worse. Damp walls carry dissolved salts to the surface, and once those salts are in the masonry they pull moisture out of the air on humid days. A wall can look dry in July and sweat in November.
What lime wash does for the outside
Traditional Algarve houses are painted with lime wash, called caiação locally, and it was historically redone every year or two, often before a festival or the start of summer. It is thin, cheap and breathable, and it reflects heat. It also goes chalky and leaves a white mark on your hand if you rub it, which surprises people who expect modern masonry paint. That chalkiness is normal. Paint that peels away in sheets is a different matter, because it suggests a plastic coating is sitting on a wall that wants to breathe.
What to look for at a viewing
Tap the lower part of the walls with your knuckles. A hollow sound means the render has lifted away from the masonry. White crystalline deposits are salts the water has carried out. A tide-mark of damp at the base of a wall, often up to a metre high, points to moisture rising from the ground, though a blocked drain or a gutter that overflows onto the wall can produce the same stain.
Look up as well. A leaking roof soaks walls from above, and an old tiled roof patched with mismatched tiles is a sign that water has been getting in for a while. Check where downpipes discharge. If they end at the foot of a wall with no drain, the wall has been taking a soaking every winter.
Questions worth asking
Ask who did the last major work and whether there are invoices. Ask whether the roof was re-tiled and when. If there is an extension or a converted outbuilding, ask to see the paperwork that says it is allowed to be there. An independent surveyor or civil engineer who works with old masonry is worth paying for, especially if the house has stood empty for a few winters, because empty houses damp up quickly with nobody opening windows.
The same rules apply at home
None of this is peculiar to Portugal. A solid-wall Victorian terrace in Leeds or Bristol behaves in much the same way, and the usual mistakes are the same too: cement pointing, gypsum plaster on old brick, vinyl paint on walls that need to dry out. Lime plaster and breathable paints cost more per square metre. They also stop the damp from becoming someone else’s problem in ten years, and that someone is often you.
