Still the most popular system in use and involves drilling holes at the base of walls and the pressure injection of a suitable water-repelling fluid together with the removal and replacement of any damp plaster internally. This system usually relies on the new waterproof plaster to hold back any dampness in the walls as most treatment companies do not ensure that the brickwork being injected is totally saturated. For a brick to be an effective damp-proof barrier it needs to be injected for approximately 20 minutes and therefore to treat an average sized house effectively it would take at least two days and as most injecting jobs are finished in around 3 or 4 hours then there is unlikely to be any proper water-proofing effect from the damp-proofing fluid. For more information on injection times please refer to an article by I'Anson S J & Hoff W D (1990) Chemical Injection Remedial Treatment for Rising Damp - II Calculation of Injection Times. Building and Environment Vol 25 No1 pp 63-70.

Full treatment including re-plastering to an average sized house can easily exceed £5,000 and it is not just the expense to worry about but there is usually a lot of disruption internally with the removal of wallcoverings,skirtings etc and then all the hassle of re-decorating after allowing the walls to dry out. The only time we find this system to be of use to clients is when they just want drilling/injecting from the outside to be done in order to obtain guarantees when selling a house.

A more recent innovation in the injected damp course market is the use of gels and creams which are squeezed into pre-drilled holes using a large mastic gun. These materials have only been used for the last 5 years or so and there is no evidence to indicate whether they are effective or otherwise but somehow it does not seem likely that they will be as effective as broken down physical slate or bitumen damp courses that they are intended to supersede.

SIPHON TUBES-DUTCH METHOD

The Dutch Method ( including Schrijver Systeem and Holland Damp Proofing) is heavily promoted in the national press as the latest infallible approach to curing rising dampness but it is probably the biggest load of Hocus Pocus to come out of Holland since the band Focus had a hit of that name in 1973.

While it may appear feasible that this damp treatment system may work all you are getting in effect is nothing more than a series of air bricks placed around the base of the walls, and in some case have the system extended to the first floor as can be seen in the examples we have seen recently. There is no independent scientific evidence to show that these devices could drive away rising damp, penetrating damp or condensation and claims made by Schrijver have never been substantiated and the Advertising Standards Authority ordered that such claims be removed from any further adverts.

If you are considering using this system then please take a moment to look at the photos below to see how your property would be irreversibly disfigured at a cost of several thousand pounds for very little proven benefit. You would be better off getting your builder to install a few extra air bricks at the base of the wall to help to remove excess moisture.

ELECTRO-OSMOSIS

Electro Osmosis is a system first discovered in approx 1800 by the physicist Reuss in an experiment which showed that water could be forced to flow through porous clay diaphragms when an external electric field was applied. Flow is initiated by positive ions and is directed from the anode (positive anode) to the cathode ( negative electrode) reversing the polarity of capillary action. In 1930, the Ernst brothers in Switzerland developed a system of applying electro-osmosis to drying out foundation walls. Three Hungarians, Miklos Lipscey, Imre Biczok and Zoltan Horvath, developed the system in Hungary, Paul Wieden did so in Austria and Dinu Moraru in Yugoslavia, and it was introduced in a patented system to Britain by W. J. Holmes of Rentokil and this system was used between 1962 and 1974 in over 55 000 houses before being superseded by the ever popular injected damp-proofing systems still used to this day.

However as the green lobby has grown there has been a resurgence in the use of electro-osmotic systems as a chemical free damp-proofing option and they generally consist of a titanium wire being installed at the base of the all walls and a small electrical charge applied. This system still involves a lot of internal disruption as the wire has to be fitted in mortar joints and all skirting boards will have to be removed to facilitate this. As with chemical damp-proofing plaster will have to be hacked off at least one metre high and then replaced with a waterproof render. This system may be chemical free but it is still quite expensive and the householder also has the hassle and mess of plaster being removed and the replacement of skirting etc after the work has been completed

PHYSICAL DAMP COURSING

The Building Research Establishment, in its Digest 245, confirms that a physical dpc is the only completely sure method to cure rising damp but is very expensive, involving sawing out sections of a mortar bed and then inserting physical membrane.

Bespoke cutting equipment is used to cut a section through the wall, of up to 1m in length. The dpc is then placed in the slot, bedded on mortar, with spacers inserted along the section to support the wall and compress the mortar. This wall is then repointed to create a finished job that is both neat and tidy, and – more importantly – effective. After the first section of wall is finished then the next metre of wall can be treated. It is a labour intensive and disruptive process but the work can be guaranteed for 50 years.

Usually we are only called upon to treat brick walls but large stone walls pose can also be cured with this method. Any large stones are removed, and this also gives use the opportunity to inspect the wall and confirm its integrity and wall thicknesses of up to 1m can be accommodated.

The lifespan of a physical damp course is far longer than any chemical damp-proofing and it creates a total barrier against rising damp.

ENVIRONMENTAL CONTROL

Physical damp-proof course have been required to be inserted into all buildings constructed since approximately 1875. Initially this would have been a horizontal layer of slates overlapping to form a continuous barrier at the base of the wall, usually at the same height of the air bricks and in the 1930’s this was replaced by bitumen which has now given way to the plastic rolls of dpm that can be purchased from any builders merchants.

Slate damp course are still fairly effective in controlling dampness and often there is no need for any replacement damp-proof courses as most cases of ‘rising damp’ are in fact usually low-level penetrating dampness where water is sitting at the base of a wall or the original damp-proof course has been bridged, both of which create a ‘moisture reservoir’ allowing water to be drawn into the wall by capillary action and this then appears as rising damp internally.

Instead of installing a chemical damp-proof course it is usually easier and cheaper to tackle the problem externally by reducing ground levels or installing drainage channels to prevent bridging and repairing any drainage and guttering defects which may be causing ponding externally. Once these works have been carried out then the walls will dry out gradually and there is usually no need to remove plaster internally so as well as saving money by not having to have damp-proofing work done then all the mess and disruption of plastering and re-decorating internally is also avoided.

Even if there is any slight passage of moisture through the old damp course it rarely causes any problems internally as the rate of evaporation from the wall above the damp course is usually greater than the uptake of moisture below the damp course.

Inadequate sub-floor ventilation is often a cause of dampness in walls as this tends to cause a build up of moisture in the floor void which can condense on the exposed masonry and timbers. Much of the condensate will be above the damp course and will then migrate upwards to appear as ‘rising damp’ internally. The easiest way to deal with this is to install extra air bricks at the base of the walls and ensure that there is an adequate through draught of air to remove moisture from the void, this will also help to reduce the moisture level of floor timbers and reduce the risk of decay and infestation.

The cost of a damp survey can be found here and can be arranged by phoning 0800 028 1903 or click the enquiry button to the left of the screen.