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How to identify and deal with rising damp

We asked expert Andy Barber from Which? Local-recommended Refresh Property Services & Consultants in London for advice on identifying and dealing with rising damp.

What causes rising damp in period properties?

Rising damp on a bedroom wall

Rising damp can cause unsightly discolouration or staining of walls

Since the 1840s, the majority of homes in the UK were fitted with damp proof courses (DPCs).

Typically made from slate or bitumen, period property DPCs can fail with age and are susceptible to the slight and normally occurring movement of a building.

When a DPC fails, a house becomes vulnerable to rising damp – the upward movement of water from the ground. The result can be unsightly and can cause damage to surrounding decorations and timbers.

How to identify rising damp

A qualified surveyor should diagnose a dampness issue prior to treatment, but a process of elimination will help you to roughly evaluate the problem and seek relevant advice.

Broadly, there are four types of dampness:

Type of dampnessHow to identify
CondensationCaused by an imbalance of heat and ventilation. Usually seen as droplets on windows or mould on walls and concealed areas. A presence of mould on the suspect area means it’s unlikely to be rising damp.
Penetrating dampnessExternal leaks from guttering, flashing, window frames or badly maintained pointing and render are common culprits. High external ground levels and internal plumbing could also be to blame. A thorough inspection should identify the cause.
Salt contaminationSalts present in soot can travel through plaster and absorb moisture from the air, meaning this problem is usually found on old, sealed-up chimney breasts. Capping chimney pots can reduce this risk.
Rising dampSymptoms of true rising damp include decay of skirting boards and timber floors, discoloured or crumbling walls and peeling paint and wallpaper. Rising damp isn’t usually seen more than one metre above ground and often has a characteristic white band of salts at the highest point.

Treatment of rising damp

Beware of unnecessary treatment

In an undercover damp-proofing investigation (published in Which? magazine in January 2012), we found that households could be spending hundreds of pounds on unnecessary damp-proofing treatment.

Seek advice from an independent specialist and get quotes from at least three treatment companies.

1. Removal of contaminated plaster
The ingress of ground water may cause salty deposits which weaken the plaster and can absorb dampness from the surrounding air. Contaminated plaster must be removed.

2. Injection of a new damp proof course
A chemical solution is injected into the mortar. It creates a water-resistant band throughout the thickness and length of the wall.

3. Re-plastering
Although a newly injected DPC will prevent further dampness from entering the wall, residual moisture will remain until it dissipates through natural evaporation. To prevent further problems, the wall should be re-plastered using a cement render with waterproofing and salt-inhibiting additives.

Cost to treat rising damp

The cost to fix rising damp varies greatly from company to company. Most calculate the cost according to the time taken to carry out the works, rather than by the size of the damp problem.

A 10m section of wall could cost between £1,000 and £2,500 to fix.

Preventing rising damp

Steps, paving or anything else that raises the external ground above the level of the DPC ('bridging') can cause damp problems.

You should also keep external masonry, guttering and rainwater pipes properly maintained.

About our expert trader

Andy Barber is director at Which? Local-recommended Refresh Property Services & Consultants in London. 

The business specialises in damp and timber treatment, basement waterproofing, condensation control and cellar conversions.

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