Rising damp in masonry

How to recognise it

Rising damp has an unmistakable signature: it starts at the bottom, stops at a fairly constant level, and leaves a band of salt efflorescence and crumbling plaster. It is seasonally stable, unlike condensation, which appears on thermal bridges and varies with how the room is used.

The salts are the trickiest part. Nitrates and sulphates carried by the water crystallise on the surface as the water evaporates, and the pressure of crystallisation breaks up the plaster. A new render applied without treating the salts degrades within months.

Why low-pressure injection

Among the available technologies — mechanical cutting, electro-osmosis, macroporous renders — the low-pressure injected chemical barrier remains the most flexible. It adapts to brick, stone, mixed or cavity masonry, requires no invasive structural work, and allows working from one side of the wall only, preserving existing plaster and frescoes.

The principle: a gel or liquid based on monomeric silane is injected into horizontal holes at the base of the wall, migrates into the pores and capillaries and forms a permanent hydrophobic barrier that blocks rising damp without compromising vapour permeability. The masonry above the barrier can then dry out.

The stages on site

Removal of the degraded plaster and preparation of the wall. Drilling with a 12–16 mm diameter and 10–20 cm spacing along a horizontal line. Insertion of the injectors. Injection of the gel or liquid at low pressure. Treatment of the residual salts with a converting solution, which turns chlorides and sulphates into insoluble compounds. Finally, application of a macroporous renovation render, which accommodates crystallisation inside itself rather than at the surface.

Drying times

The barrier acts immediately, but the wall takes months to dry: roughly one centimetre of thickness per month, depending on thickness, material and ventilation. This is the expectation that must be clarified with the client before starting, because disappointment almost always comes from here.