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.

Penetrating Damp

Penetrating DampPenetrating damp (above ground level) is usually from a source such as wind driven rain, causing

moisture to enter the structure in a horizontal direction. Gravity may cause the downward movement of the resulting dampness.

Causes of penetrating damp may be from sources difficult to control such as defective brickwork, cracked render, faulty pointing, poor flashings or rainwater goods. The cause can also emanate from a defect within an adjacent property outside the owners control.

Penetrating damp has been proven to be responsible for a high percentage of dry rot attacks found in

Penetrating damp can create isolated patches of dampness that increase in size after periods of heavy rain and tend to disappear in long dry spells of weather.

Treatments

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.

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

London

01962 706188

Winchester

01276 66466

Camberley