Part of Ward Property Services UK LtdDamp
What Causes Rising Damp?
How rising damp works
Masonry is full of fine pores. Where those pores are in contact with wet ground and there is no barrier in the way, water is drawn upward by capillary action until the rate of evaporation from the wall face balances the rate of supply. That balance point is what produces the classic tide mark, usually between 600mm and 1200mm above floor level.
The water carries dissolved ground salts with it. When it evaporates at the wall surface, those nitrates and chlorides are left behind in the plaster. They are hygroscopic, meaning they attract moisture from the air, so contaminated plaster stays damp even after the wall behind it has dried. This is why replastering is part of the cure and not just cosmetic.
The real causes we find in Surrey
A genuinely absent damp proof course is only one possibility, and in Banstead and its neighbouring towns it is not the most common. Bridging is. A patio, driveway or flower bed raised above the DPC line allows moisture to enter the wall above the barrier. External render carried down over the DPC does the same. Debris and mortar droppings in a cavity form a bridge across it.
Original slate and bitumen damp proof courses can also fail — cracked by settlement, damaged during a previous alteration, or breached where a new doorway or extension was formed. Each of these is a specific, findable defect, and finding it is what makes the repair proportionate.
Telling it apart from other damp
Condensation appears on cold surfaces, not just at low level, and typically brings black mould in corners and around windows. Penetrating damp fluctuates with rainfall and can appear at any height. A plumbing leak tends to be localised, constant regardless of weather, and often warmer to the touch on a heating pipe run.
Instrument readings settle the question. Surface meters alone are not enough because salts and foil-backed plasterboard give misleading results. Deep-wall drilled samples analysed for moisture content and salt profile tell you whether groundwater has genuinely been travelling through the wall.
What actually fixes it
Where bridging is the cause, removing the bridge is the fix — lowering ground levels, cutting back render, clearing a cavity. No injection required. Where the DPC is genuinely absent or failed, a silicone cream damp proof course injected at mortar bed level forms a new water-repellent band, followed by removal of salt-contaminated plaster and a renovating plaster system.
What does not work is painting over it, applying a waterproof sealer to the internal face, or dry-lining without addressing the source. All of these trap moisture and usually move the problem rather than solving it.
Common questions about this topic
Is rising damp covered by insurance?
Almost never. It is treated as a maintenance issue rather than sudden accidental damage.
How much does treating rising damp cost?
It depends entirely on the length of wall and the extent of replastering. Correcting a bridged DPC can be a fraction of the cost of a full injected system.
Need professional advice?
Book an independent damp survey and get a written diagnosis for your property.