Q. WHAT IS RISING DAMP?
A. Rising damp is the upward movement of moisture through walls and sometimes floors by capillary action from below the ground. It can rise to 900mm or more in walls, depending on the masonry type, water-table level and evaporation rate. Salt deposits generally form a horizontal tide-mark, below which there is discoloration. Floors can display moist patches and staining. Rising damp is distinct from other forms of dampness, such as rain penetration and condensation, which require different solutions.

Q. HOW IS RISING DAMP DIAGNOSED?
A. Rising damp is widely misdiagnosed on the basis of high electrical moisture meter readings alone. Elevated readings occur not infrequently in old buildings that are virtually dry, due to salt deposition from evaporation, or can indicate another problem altogether, such as penetration from rain splash. If rising damp exists, there will be visible indications too, such as an accompanying tide-mark, but not, for example, the external green staining symptomatic of rain penetration. Tests to determine moisture levels within the wall thickness can help rule out surface condensation.

Q. HOW CAN I CONTROL RISING DAMP?
A. Measures that help your building ‘breathe’, such as replacing hard cement render or pointing with a more suitable lime-based mortar, may be the best solution. Conversely, applying water-proof renders and coatings can exacerbate damp problems. Where a floor has a damp proof membrane that is displacing moisture into the bottoms of walls, this might be replaced with a ‘breathable’ construction. Alternatively, a ‘breathing’ strip for evaporation may be cut through the floor around the room perimeter and infilled with a material such as lime concrete or grated over. Externally, ground works and improved drainage can assist. A French drain can be a very effective means of reducing moisture levels at the base of a wall.

REPAIRING RISING DAMP – LPOC’s EXPERT TIPS

• Lime plaster should normally be used for any repairs.
• Salt-resistant plasters tend to just temporarily disguise continuing damp problems and may require listed building consent.
• A poultice of whiting and water is an old method of removing patches of residual salts from plasterwork. Decoration with paints such as limewash and soft distemper, where possible, will maximise ‘breathability’. Avoid the use of modern non-breathing paints.
• Be cautious of unnecessary damp proofing, especially if requested by a mortgage lender during a purchase. Always speak to an independent chartered surveyor or consultant, not a contractor or so called ‘damp specialist’.

Are you worried about damp and your listed building? It is important to note that each listed property is unique, and whilst associated issues with older properties can be widely known, each case is different. Due to this we highly recommend that you personally speak to a specialist on the phone to discuss your individual property. We welcome you to contact us on 01795 844939 for impartial advice, and we will endeavour to point you in the right direction and to help solve your problems.

You may also like to take a look at The Suppliers Directory where you can access specialist companies who you can approach with confidence. Further information on damp and a whole host of other essential information, technical information sheets and step-by-step guides for listed property owners can be found in the LPOC Logbook which all members receive. Listed Heritage magazine also features regular information and case studies. To find out more about membership, click here.