rising damp in walls is water from the ground travelling upward inside the material, so any remedy has to reach that material. Paint works on the surface, while a dehumidifier works on the air. So neither one touches the climb.

Expect rising damp in walls to run over seasons rather than weekends. A wall gives up its water at its own pace, and nothing sensible hurries it.

How to be sure you are looking at rising damp in walls

Three faults leave a similar stain, so tell them apart first. Rain crossing the outside face darkens a patch within a day of a storm. A leaking pipe, though, keeps one area wet whatever the weather. Water forming on cold plaster gathers in the coldest corner, often behind furniture.

rising damp in walls has a quieter signature. The band sits low, within about a metre of the floor. Its top edge also runs roughly level. It climbs through autumn, then falls back in summer.

So measure that height and photograph the wall. Write the date on the picture, then repeat every month. Six months of that record says more than any single reading. Our article Condensation or rising damp: how to tell the difference takes the causes one at a time.

The physics under the plaster

Brick, stone and lime mortar are porous. Their pores form microscopic channels, and water climbs them with nothing pushing behind. Physicists call the effect capillary action. Narrow channels lift water higher than wide ones, so fine lime mortar carries the mark furthest. Our article ATE: anti-damp device for damp walls and rising damp treatment follows the whole climb from the footings.

At the surface the water evaporates and leaves its dissolved salts in the plaster. They crystallise, they grow, then they crumble the render from within.

Salt in turn slows rising damp in walls down. The crystals take up moisture from the air on their own account. So a heavily salted wall stays damp even where the climb has eased. Our article Buying a house with damp walls: what to check covers that stage.

Three routes out of rising damp in walls, and what each one costs

Which route suits you depends on the wall and on your appetite for disruption. Resin injection means drilling the wall at intervals and pumping in a cream meant to form a barrier. It is heavy work, since the whole run of wall has to be reachable.

Outside drainage with a fresh render means digging, scaffolding and weeks of disturbance. Neither route is wrong. Both, though, put a building site in a house that people live in.

The third route asks for two wall plugs. The ATE is an electromagnetic polarity inverter. It sends very low frequency electrical pulses through the masonry, hour after hour. Its design principle comes from electro-osmosis. The pulses act on the electrical charges where the water meets the wall of the pore, so they work against the climb and favour the return of the water towards the footings.

That is a design principle, and we claim nothing beyond it. Nothing is pumped out and nothing is heated. So the wall dries by evaporation, over 18 to 24 months. Our article Damp wall after renovation: why the problem comes back sets out that route in detail, while Persistent musty smell: causes and useful actions compares the ATE and ATG ranges.

Choosing the model that covers your walls

Each unit works over a radius, measured from the point where you fix it. So measure the walls you want to treat, then pick the model whose radius covers them from a central position.

Model	Range	Price
ATE LC15	7.5 m radius, 15 m across	€1,290
ATE LC30	15 m radius, 30 m across	€1,590
ATE MAX	30 m radius, 60 m across	€1,990

Every unit draws 0.75 W on a 12 V supply and measures 322 x 232 x 32 mm. Each one carries a 10-year manufacturer warranty. All three are made in France, and delivery costs nothing. The ATG follows the same design principle with no mains supply, which suits a wall with no socket within reach.

Fitting the unit yourself

Fix it to a load-bearing wall or a partition wall, between 30 cm and 1 m above the floor. Aim for the centre of the area to treat. Two wall plugs and a socket, less than an hour, no tradesman.

Never fix it to plasterboard and never to insulation. The back of the unit has to touch the masonry. Keep 1.50 m between the unit and any other electrical equipment.

If the bottom of the wall carries a waterproof cement render, cut that render back over ten centimetres or so. Then the water reaches the air and evaporates, instead of sitting trapped behind a sealed skin.

The two years that follow

So take the loose material off first. Flaking paint, blown render and any coating that traps vapour all come away. Then the wall stays bare, with air moving across it.

Then brush the white bloom off dry as it returns. It comes back for a while, and that cycle is normal while rising damp in walls eases.

Leave decoration until the end. Lime plaster and a vapour-open paint let the masonry carry on drying. A plastic emulsion holds the water in. Our guide Blistering paint on a wall: understand the issue before repainting runs through the options.

Keep an eye on the outside as well. A blocked gully or a raised flower bed feeds rising damp in walls faster than any unit can work.

Frequently asked questions

How high can rising damp in walls climb?

Water rarely travels much beyond 1.5 m above ground level, so most walls show a band under a metre. Higher marks usually point to a leak or to rain crossing the outside face.

Will a dehumidifier deal with rising damp in walls?

A dehumidifier dries the air in the room. It changes nothing inside the masonry, so the climb carries on behind the plaster.

Which walls can the unit be fixed to?

Any load-bearing wall or solid masonry partition works, provided that the back of the unit touches the masonry. Plasterboard linings and insulation are ruled out.

When does a wall with rising damp in walls start to look different?

Visible results come between 18 and 24 months. A thick stone wall takes longer than a brick partition, since it holds more water to begin with.

Does fitting the ATE need an electrician?

No. It plugs into an ordinary socket, draws 0.75 W and fixes to the wall with two plugs in under an hour.

Before you order

The unit treats rising damp and capillary damp, and nothing else. It does nothing for a leaking gutter, for driving rain, or for poor ventilation. Those three causes together remain more common than capillary damp, so rule them out first.

Rather than guess, send us two or three photos. One of the bottom of the wall, one of the room, one of the outside face. We read them and tell you which model fits, or tell you plainly that your problem lies elsewhere.

See the ATE and ATG models · free delivery, 10-year warranty, made in France