Damp treatment for rising damp involves either curing the source of the problem or masking its effects.
Finding the cause of the problem is the key to any successful long term damp treatment. The property should be closely inspected to ensure the existing DPC has not been bridged. Remove any earth that is within 150mm of the DPC or is blocking air vents.
Remove any external render which is breaching DPC and add a bell cast, also remove internal render to above the DPC.
Damp Treatment French Drain
Improving drainage around the property and lowering pathways and drives to below D PC will allow the lower courses of bricks to evaporate excessive moisture during the drying phases. A simple damp treatment but effective method of reducing sustained wetting against the external brick work is to install a breather trench. This will allow rapid evaporation of moisture from the face of the external brick work.
Damp Treatment for Cavity Wall Clearances
Adequate sub floor ventilation is the most important component of any damp treatment so cavity walls should be checked and cleared of blockages that prevent the internal vent from allowing air to circulate under the sub floor.
Sub floor areas should be checked for wet and dry rot and any timber built into the internal walls or timbers lying on sleeper walls without an effect damp barrier.
Damp Treatment using a physical DPC
The only certain way of introducing an effective DPC is to insert a new physical membrane. This technique requires cutting the old lime mortar bed joint through the entire thickness of a (9 inch) solid wall. An adapted chainsaw is usually used to cut out the mortar bed. The membrane inserted into the wall and new mortar is pushed back into the wall to complete the work.
There are disadvantages to this to this old traditional method which are cost, the time required and the disturbance which it will create.
Damp Treatment using Chemical Injection
These can be used in most types of structures, although rubble infilled walls can be difficult to treat successfully. This damp treatment involves inserting specially formulated products into closely spaced holes in brick or mortar courses along a DPC line. Their efficiency depends on how well the product penetrates the damp structure and its subsequent success during curing.
Silicate or aluminum stearate water repellents are either injected at high pressure or transfused into the wall under gravity or at low pressure. High pressure systems are generally used with solvent based silicones and aluminum stearates; transfusion methods are limited to the application of water based silicones basically in the form of the water soluble sodium methyl siliconate. The water repellents are pore liners rather than blockers and so allow the passage of some water vapor whilst preventing the rise of liquid moisture.
The repellents are not intended as a damp proof barrier against a substantial positive pressure of water and are not suitable in basement areas subject to high water tables and penetrating damp.
New chemical injection products are known as creams or gels. The cream is a concentrated viscous silane / siloxane emulsion, inserted by a gun through 12mm diameter holes drilled at the base of the perpends and at intervals of up to 120mm along the mortar coarse.
Damp Treatment using Ceramic Tube Vents
In 1919, during the Great War peace conference, a member of the British military delegation noticed something interesting in the Palace of Versailles: a row of small circular vents along the bottom of a wall. After some inquiries the delegate – one General Brown – found that the vents concealed ceramic tubes set into the wall for damp proofing, a process that had been patented in 1908 by a Belgian, Monsieur Knapen.
General Brown introduced the Knapen tubes into Britain under license, and apparently enjoyed some commercial success with British Knapen Ltd before selling up. Ceramic tubes continue to be made, marketed and installed in British homes.
The only trouble with a damp-proofing system which uses ceramic tubes is that it doesn’t work.
At first sight, the idea of drilling holes in a wall to remove moisture might seem logical. After all, increasing the exposed surface area should assist evaporation, shouldn’t it? But there was always supposed to be more to the tubes than that. The fine pores of the ceramic clay would actually draw dampness out of brick and stone. The angle at which the tubes were stuck in the wall would cause the moist air to flow away by gravity. It was even thought that the Dutch clay from which the tubes were made had special properties.
But any physicist will tell you that the system cannot work because the finer the pores, the greater the capillary action, or suction – and this makes a material hold on to its moisture, not dry out by evaporation. Any evaporation at the surface of the tubes would cause a build-up of dissolved salts, which would attract moisture from the air and actually make the wall damper. These suspicions were verified by experimental work published in Germany in the 1960s. Ceramic tubes do not make walls dryer, and in some cases they can make them wetter.
Even the damp-proofing industry trade body, the British Wood Preserving and Damp Proofing Association (BWPDA) has a code of good practice which advises against using ceramic tubes.
But nobody in the building game ever let a few facts fog the issue. The contents of foreign-language science journals do not find their way easily into the British press. So 30 years after they were shown to be worthless, ceramic tubes are still being marketed, and even described in construction textbooks as a proven way of keeping walls dry.
Damp Treatment Survey
The need for the correct damp proofing advice is so important there are so many variables only our experienced surveyor can choose the best method of repair for your property.
Damp Treatment Methods Types
Damp Proof Course (DPC)
The DPC is a barrier placed in the construction to prevent rising damp through capillary action. Rising damp is the effect of water rising from the ground into your property. The damp proof course may be horizontal or vertical. A DPC is layer is usually installed at least 150 mm above the ground. This will depend on the internal floor height.
The methods for installing a new DPC are described generally as “traditional” (the insertion of a physical DPC) or “nontraditional” (the use of barrier creams or silicon treatments under high or low pressure). We strongly recommend that you consider nontraditional methods only if it has been awarded an Agrément Certificate. Chemical injection is the only method that currently satisfies this requirement. Chemical injection systems can be used in most types of structure, although flint walls and rubble infilled walls can be difficult to treat.
Damp Proof Membrane (DPM)
The DPM is a membrane material applied to prevent moisture directly rising under the floor slab. A common example is polyethylene sheeting laid under a concrete slab to prevent the concrete from gaining moisture through capillary action.
Integral Damp Proofing
In concrete this involves adding products like SBR latex a Styrene Butadiene Copolymer Latex which is specially modified to be compatible with cement based mixes (ordinary Portland cement or high alumina cement). It may be incorporated into cementitious renders, screeds or patching mixes in order to improve adhesion and abrasion resistance. It can be used internally or externally and in areas of continuous or intermittent water contact.
Cavity Wall Construction
Is the construction of two walls approximately 75mm apart, held together by wall ties. The outer external wall takes the weathering keeping the internal wall dry. Then the outer wall in times of dryer weather uses evaporation to disperse moisture from the cavity. A good air flow is a must in cavity wall construction.
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