How to Beat Damp

Damp and condensation are twin spectres, which often go hand in hand to cause damage to fabric, furniture and fittings in the home. Much can be done to relieve the problems by abating the conditions causing condensation and eliminating structural and related problems which allow damp to penetrate the structure.

Rising damp

This often occurs in older structures without a damp-proof course (DPC), or where an existing DPC has broken down. Water rises from the ground and, through capillary action, is absorbed into porous brickwork and through the plaster. The result is a band of staining, usually at skirting level, paper peeling from the walls and efflorescence – mineral salts drawn out on to the exterior brickwork surface.

Timber joists and floorboards adjacent to the failed dampcourse area may be affected by wet or dry rot.


It is necessary either to renew, repair or insert a damp-proof course, or to use a suitable proofing alternative. DPCs should be some 150mm above exterior ground level. They can be inserted by the following methods:

Cutting out

By cutting out one section of brickwork at DPC level at a time. A chain saw is needed to cut through brickwork. Insert a layer of bituminous felt or slates encased between layers of waterproof concrete. The slates are overlapped in an under-and-over arrangement.

Silicone injection

Where cutting out is not a practical proposition an injected DPC can be used. Drill holes at intervals of 230mm, using 12mm or 25mm masonry drills, at an angle of 45 degrees. Stagger the holes 100mm above floor level along the brickwork. This work can be done either internally or externally.

It may be necessary to hack back any wet plasterwork and remove skirting boards. The method of treatment varies slightly between systems. Silicone, water-resistant liquid can either be injected into the holes under pressure, a method usually carried out by specialist firms, or allowed to drip in to the wall, a method you can use yourself.

In this method, 570ml bottles, containing the silicone liquid, are inverted, placed in the holes and the liquid is allowed to permeate the wall interior. This solution will seep into the brickwork until saturation level is reached, when no more will flow from the bottle.

Bottles that empty quickly should be refilled as this indicates a natural internal cavity that must be filled.

Once a protective silicone layer is formed, the reverse of capillary action occurs. The surface tension created by the barrier forces rising dampness down.


Where cutting out or drilling are not possible, such as with thick walls or along party walls, a process called electro-osmosis can be used. This is done by specialist companies.

Copper wiring or a ribbon of copper are inserted into the walls at DPC level. These are connected to copper earth rods set in the soil.

This method utilizes the fact that an electrical charge exists, associated with the moisture rise, between the wall and the earth. The copper ribboning and earth-rods, placed carefully, create a low-resistance circuit between the soil and building.

The electricity is discharged to earth. Damp cannot rise above this charge and the walls dry out as the moisture evaporates.

Damp-proof courses

Damp patches on the inner walls of cavity walls may appear because the DPC has been broken or bridged. Earth should not be piled up against external walls above the DPC level, as the DPC becomes ineffective and there is no barrier to prevent moisture from rising up the walls. This may need only removal of debris, piled higher than the DPC.

Problems such as a break in the DPC or a mortar-encrusted brick tie in a cavity wall require drastic treatment. Sections of brickwork in the area of damp will have to be cut out to insert a repair section of bitumen felt to a DPC or for access to a dirty brick tie.

Floors laid directly on to earth, without a damp-proof membrane, may give trouble. This can be temporarily remedied by covering the floor with a damp-inhibiting expoxy-pitch resin. If this fails, you will have to lift the old floor and lay a new floor over a bituminous, liquid membrane or a sheet of heavy-duty, 500-gauge polythene sheeting.

Whichever method is used, make sure the waterproof layer reaches at least 150mm, preferably cut into the horizontal DPC where this exists, up the walls to form an efficient seal.

10. November 2011 by admin
Categories: Featured, Handyman Tips | Tags: , , , , , , , , , | Comments Off on How to Beat Damp


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