Damp Specialists for Period & Listed Properties

Most of the clients who call us have already tried to fix their damp. They’ve had a damp proofing company visit, a chemical damp proof course injected, waterproof render applied to the external walls, or internal tanking installed to “seal” the problem. The work came with a guarantee. The damp came back anyway.

This is not bad luck, and it is not your fault. It happens because the standard approach to damp – the one used by the vast majority of damp proofing companies in the UK – was designed for modern buildings with cavity walls and impermeable construction. It was not designed for the building you own.

Period properties, typically anything built before 1919, and often much older – were constructed using lime mortars, lime plasters, solid walls and natural ventilation. They were designed to manage moisture through movement and evaporation. When you interrupt that system with modern materials, moisture has nowhere to go. It finds another route, it collects behind the surface, and eventually it reappears somewhere else.

The first thing we do when we arrive at your property is listen to what has already been tried. The second thing we do is look at the building and work out what it’s actually telling us.

A modern house is built to keep moisture out. Cavity walls, damp proof courses, impermeable renders, plastic membranes, gypsum plasters – the whole system is designed on the principle that water should never get in, and if it does, it should be sealed behind something waterproof until it can be removed.

A pre-1919 house does the opposite. It is built to let moisture in and let moisture out. Solid stone or brick walls absorb a small amount of water from driving rain or ground contact, and then release it back into the air as the weather changes. Lime mortar and lime plaster are porous and vapour-permeable, which means water vapour moves freely through them. Timber floors over ventilated sub-floor voids allow air to circulate beneath the building. Chimneys, sash windows, suspended floors and unsealed roof voids all contribute to a continuous flow of air through the structure.

This is not a flaw. It is the design. These buildings have lasted 150, 300, sometimes 500 years precisely because they manage moisture through breathability, not by trying to stop it.

The problem begins the moment someone treats a heritage building as if it were a modern one. Cement pointing replaces decayed lime mortar joints. A cement render is applied to the outside of a cottage “to stop the rain getting in”. Internal walls are stripped of lime plaster and skimmed with gypsum. A damp proof course is injected into solid nine-inch walls. Each intervention seems sensible on its own. Together, they turn a building that was designed to breathe into one that can no longer manage its own moisture.

The moisture doesn’t disappear. It gets trapped. And then it makes itself known – as blown plaster, salt staining, a persistent musty smell, rooms that never feel warm, and damp patches that always return.

Before we explain what we do, it’s worth being specific about what the wider damp proofing industry does to period properties across Dorset, and why these approaches fail.

Chemical damp proof course injection is the most commonly sold “solution” in the county — and the most commonly inappropriate. The injection targets a problem (true capillary rising damp) that is far rarer than the industry presents. In most Dorset properties we survey, the actual cause is something else — and the injection leaves it untouched.

Waterproof cement render and tanking seal moisture out of, or into, the wall. On a Dorset solid-walled cottage, this prevents the wall from working as it was designed to. The moisture accumulates behind the render until it finds another exit — often above the tanked line, often through the surface as crystallised salts.

Gypsum plaster on lime substrates is one of the most common things we strip out of Dorset properties. Vinyl emulsion paint over lime plaster is another. Both are vapour-resistant; both prevent the wall from breathing; both cause the underlying lime substrate to fail.

Cement repointing on lime-built masonry is widespread across Dorset, particularly on properties that were “renovated” between 1960 and 2000. The cement is harder than the surrounding brick or stone, blocks the moisture release route, and accelerates erosion of the masonry itself.

We don’t apply any of these to Dorset’s period properties. We remove them.

A Georgian townhouse, Poole — three failed treatments before us. A Grade II Georgian townhouse in Poole’s Old Town. The owners had had three previous damp treatments over a decade — chemical injection, internal tanking, and a renewed chemical injection. The damp returned each time. On survey, the actual causes were a cement render applied externally during the 1970s, a bridged DPC from a raised pavement at the rear of the property, and gypsum plaster internally that was preventing the walls from drying. Remediation involved removing the cement render and lime re-rendering, reducing external ground levels at the rear, removing the failed tanking and gypsum internally, and three-coat lime plastering the affected walls. The damp has not returned in two and a half years.

A cob cottage, Marshwood Vale — chemical injection on cob. A small cob and thatch cottage in west Dorset. The previous owner had been sold a chemical damp proof course by a national damp proofing firm. On a cob property, chemical injection achieves nothing — there’s no continuous capillary structure for the chemical to interact with, and the actual cause of damp in cob is invariably trapped moisture from inappropriate materials. Survey identified extensive softening of the cob behind a layer of modern plaster, plus failed external limewash that needed reinstating. Remediation involved removing the modern internal plaster carefully, monitored drying of the cob, fibre-reinforced lime plaster reinstated internally, and external limewash applied in a tone matched to surviving evidence. The cottage has stabilised.

An Edwardian villa, Bournemouth — condensation misdiagnosed as rising damp. A buyer of an Edwardian villa in Bournemouth had received a surveyor’s report flagging “rising damp” at the base of several internal walls. Our assessment identified the real cause as severe condensation — the property had been heavily draught-proofed by the previous owner, original airbricks had been painted over, two chimneys had been capped solid, and the gypsum-skimmed walls were cold surfaces on which moisture was condensing. No chemical injection was required. Remediation involved reinstating subfloor ventilation, uncapping two chimneys with appropriate cowls, replacing gypsum plaster with lime on the worst-affected walls, and a conversation about ventilation routines. The “rising damp” never returned, because it had never been rising damp.