rising damp

Rising Damp

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This is defined as ground water rising through the structure by capillary suction. Rising damp results in unsightly damage to internal decorations, which will lead to timber decay and heat loss through the wall. 

This can be effectively addressed by installing BBA Agrément certificated damp proof systems, to BS 6576: Code of Practice for the Installation of Remedial Damp Proof Courses in Masonry Walls. 

Removal of the plaster 

When rising damp affects a wall structure, salts contained within the ground water (‘Nitrate and chloride’ being the most common) are drawn into the wall and subsequently the plaster by capillary action. In severe cases the plasterwork can lose its key, along with visual evidence of salts, noted by the presence of staining and surface mineral salting. 

These salts are hygroscopic (they have the ability to absorb moisture from the surrounding environment). The amount of moisture absorbed being dependent on the type and quantity of the particular salt, and the humidity of the surrounding environment. In a given situation the moisture levels will vary depending on the ambient humidity. 

Hygroscopic salts can cause masonry to remain damp even though there is no source of water (capillary) ingress. Wallpaper especially can become very damp solely due to contamination with hygroscopic salts. Sufficient moisture absorption can cause wallpaper adhesive to become soft and sticky, resulting in the wallpaper to peel away from the wall. Where the wallpaper has become heavily contaminated, its surface feels sticky and may look damp/stained.

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The removal of the contaminated plaster to the correct height, and the application of new plasters to the correct specification is as important as installing the damp proofing treatments in the base of the wall. 

Failure to undertake these works correctly, including the installation of a secure ‘floor to wall joint’ were treatments are installed in walls adjacent to solid floors, will result in a failure of the system.

Drybase damp proofing system 

The Drybase damp proofing system is provided by bonding a flexible low profile watertight and salt resistant polypropylene membrane to the wall surface. In conjunction with an effective damp proofing system installed into the wall structure. 

Floor to wall joint

Where the wall areas to be treated are located adjacent to a solid floor, to conform with BS: 6576 section 6.1.5. an effective floor to wall joint must be installed to prevent moisture vapour evaporating from below the installed floor slab and area of brickwork l o c a t e d below the installed damp proof course level.

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