Rising damp

Rising damp is the action of water moving vertically through porous building material, which is in contact with the ground. This is brought about by the drying action of air on the upper surfaces which causes the wall to act like a wick, drawing water upwards from the ground by capillary action, which then evaporates from the surface into the atmosphere. The moisture will continue to rise until it reaches a height where, unless evaporation is possible, gravity pulls it down again.

Rising damp occurs because the building’s damp proof course (DPC) has broken down or is being bridged by high ground. A DPC installed during construction will be a physical layer of impermeable material. This can consist of slate, bitumen impregnated felt or plastic, for example. Many older properties do not have a DPC.

Water coming from the soil will have various dissolved nitrates, chlorides and other salts (hygroscopic ground salts) which will be carried upwards into the brickwork and plaster. As the water evaporates, an increasing amount of these salts will be deposited in the wall. As ground salts are easily dissolved they also readily attract moisture from the atmosphere.

As a result of this the plaster will always be damp or contaminated, even after the rising damp is cured. For this reason the plaster is normally removed when treating rising damp. Wood rot in adjacent timbers may often be as a result of rising damp in a wall.

Damp proofing works
Damp proofing works nearing completion

Penetrating damp

Penetrating DampThere may be a number of reasons which result in penetrating dampness into walls above external ground level. One of which could be wind-driven rain which, depending on the direction of the rain is largely out of the property owner’s control. Unfortunately, this can lead to a downward movement of moisture within the structure.

Whilst it may not be possible to control the direction and force of wind-driven rain, it is possible to prevent such rain entering the structure and causing internal damage. It is important to ensure the property is well-maintained to prevent water ingress; which could be via cracks in external render coatings, loose and missing pointing on walls and around window and door frames, defective flashings around roof structures, defective rainwater goods such as leaking or blocked gutters, down-pipes and hoppers.

If the property is not maintained, penetrating damp could result in significant damage occurring within the property including outbreaks of fungal decay (Dry Rot and Wet Rot attacks).

Penetrating damp can also result in the migration of hygroscopic salts into the internal plaster finishes which causes random and isolated patches of dampness to appear during spells of high humidity.


Damp Proof Coursing

Damp-proof CoursingWhere appropriate, PTL will install a chemical DPC system to control the problem. The chemical DPC is injected into the walls at regular intervals. There will often be a small level of moisture held in the substrate due to salt contamination even when rising damp is controlled. Re-plastering will replace the salt contaminated plaster and protect the decorated surface from any residual moisture held in the wall.

Specialist Rendering

The installation of the damp-proof course will prevent further rising dampness. However, water attractive hygroscopic salts, transmitted by the rising dampness from the soil to the brickwork will continue to attract moisture, particularly during periods of high humidity. Where this occurs to an unacceptable degree, re-plastering to the PTL specification is required. PTL employs specialist plasterers and would be pleased to provide quotations for this work.

Damp proofing case studies

Damp Proofing and Specialist Rendering – Camberley, Surrey

Following an initial inspection by one of our CSRT qualified Surveyors, on behalf of the Managing Agents and Landlord, Preservation Treatments were instructed to carry out Damp-Proofing works to this 3 bedroom Victorian semi-detached property in Camberley, Surrey.

Contact us today to arrange for a survey, and one of our surveyors will provide you with a report and quotation outlining what is causing the damp and what the best solution is.

0208 914 8189


01962 706188


01276 66466