Rising damp and condensation are not just ugly; they quietly destroy walls, feed mould, and can undermine a building’s health and value if left untreated.
What rising damp is
Rising damp is the upward movement of groundwater through porous materials such as brick, mortar, stone, and concrete via capillary action. It affects both old and new buildings and is estimated to impact a significant share of the existing building stock in Spain.
Why moisture rises
Moisture from the ground travels upwards in liquid and vapour form, driven by capillary forces in tiny pores. As water evaporates at the surface, salts are left behind, concentrating inside the wall and gradually breaking down masonry and finishes.
Vulnerable materials and environments
Highly porous materials such as bricks, cement blocks, natural stone, and untreated timber absorb and transport more water, making them especially prone to rising damp. Humid climates, high rainfall, clay soils and a high water table all increase the risk, as soil holds more water and feeds more moisture into foundations.
Ventilation myths and indoor humidity
Poor ventilation traps moisture indoors, increasing condensation, mould growth and damage to finishes, even if the original source is in the walls or floor. Simply “airing” a damp house by opening windows in winter can backfire when outdoor air is cold and humid, since it cools internal surfaces and can actually raise condensation and heating costs without fixing the root cause.
Prevention and effective treatment
Good detailing during construction or renovation, correct levels and drainage, proper air movement and moisture control and regular maintenance reduce the risks. Where damp already exists, solutions include actual physical damp-proof barriers in suitable cases, removal and replacement of damaged finishes, and mineral systems, insulation or breathable salt-blocking mortars like Diathonite Deumix+ that allow moisture to move while controlling salts.
Myth busting: “airing always helps”
One of the most persistent myths is that throwing windows wide open every day will dry out a damp house, regardless of outside conditions. In reality, if the outside air is colder than indoors, opening windows for long periods cools down walls and surfaces; when warm, moisture-laden indoor air then meets these colder surfaces, its relative humidity rises, and water condenses out, worsening visible damp and mould.
Short, controlled ventilation works best:
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Air out quickly when outside air is cooler and relatively dry, then close up and heat so internal surfaces stay warm.
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Combine this with extraction in kitchens and bathrooms and, where necessary, dehumidification, so that moisture is removed from the building rather than moved onto colder walls.