The right damp proof coating for walls depends on what the wall is doing. So the job starts with a look rather than a list. Ground water, driving rain and water forming on cold plaster each leave their own mark. So read the mark, then choose the damp proof coating for walls.

Buy in the wrong order and the money goes on the wrong layer. A wall fed from below lifts a fresh coating within a season, whatever the damp proof coating for walls promises.

Read the wall before you buy damp proof coating for walls

Start with a tape measure. Damp from the ground keeps low, usually within a metre of the floor. Its top edge runs fairly level. So pencil that line in, because the height decides which damp proof coating for walls makes any sense.

Then watch the calendar. A wall fed from the ground darkens through autumn and fades in summer. A patch that spreads after a storm comes from the outside face. Beads of water on the coldest corner belong to the air in the room instead.

Finally, walk round the house with a spirit level. If a path or a flower bed sits higher than the floor inside, the wall drinks from it. So no damp proof coating for walls changes that. Our article Condensation or rising damp: how to tell the difference takes each sign in turn.

Why the masonry keeps drinking

Stone, brick and lime mortar are full of microscopic channels. Water climbs them the way tea climbs a lump of sugar, an effect known as capillary action. The finer the channel, the higher the water travels. So fine lime pointing can carry the mark to waist height. Our article ATE: anti-damp device for damp walls and rising damp treatment follows that climb from the footings up.

At the surface the water evaporates, though the minerals it carried stay in the plaster. They crystallise, they swell, and they break the render apart from behind. That is why a wall looks sound in June and blisters in November.

Those crystals also pull moisture straight out of the air. So a salted wall still feels damp long after the climb has eased. Any damp proof coating for walls laid over it rests on ground that keeps moving. Our article Buying a house with damp walls: what to check explains where the white bloom comes from.

Working on the masonry rather than the surface

The ATE is an electromagnetic polarity inverter. It plugs into an ordinary socket and sends very low frequency electrical pulses through the masonry, without a break. 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.

We put that no higher than a design principle. Nothing is drawn out and nothing is warmed, because the wall dries by ordinary evaporation. So visible results come between 18 and 24 months, and a thick stone wall sits at the slower end of that range.

The ATG does the same work as a geomagnetic polarity inverter, with no supply at all. Unlike a damp proof coating for walls sold in a tin, neither unit touches the finish. Our guide Persistent musty smell: causes and useful actions sets the two ranges side by side.

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.

Where damp proof coating for walls fits into the year

Once the cause has been dealt with, give the wall months of bare surface and moving air. So strip the flaking paint, cut back the blown render and leave the masonry open.

Then pick materials that let vapour through. Lime plaster and mineral paint keep releasing moisture. A plastic emulsion or a cement render holds it in and pushes the mark higher. Our guide Blistering paint on a wall: understand the issue before repainting compares the finishes case by case.

A damp proof coating for walls earns its place at that point, over masonry that has dried. If a building site holds no appeal, our article Damp wall after renovation: why the problem comes back describes the quieter route.

Frequently asked questions

What can I put on a wall that is still damp?

Nothing that seals the surface. Brush off the loose material, leave the plaster bare and let air move across it until the masonry has dried.

Is a cement render a good damp proof coating for walls at the foot of a wall?

A waterproof cement render keeps water inside the masonry and sends the mark higher up. A renovating lime render holds the salts in its own thickness and lets vapour out.

How do I know the damp comes from the ground?

Ground damp keeps to the bottom of the wall, roughly within a metre of the floor. It brings salt and crumbling plaster with it. A patch that appears high up after heavy rain comes from outside.

Does the old plaster have to come off before any damp proof coating for walls?

Take off whatever is blown or hollow, since sound plaster can stay. Bare masonry dries faster, so most people strip the lower band and redecorate at the end.

What does the ATE cost to run?

It draws 0.75 W on a 12 V supply, so a year of use costs very little. The ATG needs no supply at all.

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