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Treatment options for rising damp
INJECTED DAMP-PROOF COURSE
Still the most popular system of installing a damp-proof course and are usually offered by damp-proofing contractors whose installation is covered under British Standard (BS 6576:2005- Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical damp-proof courses ) and usually comes with approval through a British Board of Agrément Certificate BBA ( example- Agrément Certificate 95/3210 for Triject Chemical Damp-proofing system issued to Triton Chemicals).
Holes are drilled into the thickness of the wall to attempt to saturate a zone usually around 75-150mm high at approximately 150mm above the external ground level at various centres and depths. A damp-proofing fluid, usually based on silicons or aluminium stearates, is then pressure injected into the wall. 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.
This system usually relies on a dense sand/cement waterproof plaster to hold back any dampness in the walls as most treatment companies can never be certain that the brickwork being injected under pressure is totally saturated as this leads to viscous fingering whereby the damp-proofing fluid follows the line of least resistance leading to an ineffective chemical damp-proof course. The specification of the plaster is usually a dense sand/cement render which itself will prevent the passage of moisture onto internal wall surfaces.
Full treatment 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.
In many cases damp-proofing works are only undertaken as a part of a mortgage condition to obtain a guarantee against the recurrence of rising damp.
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. They are touted as a quick and easy way of inserting a damp-proof course but in practice these materials are hard to use leaving globs of cream or gel oozing out of the holes and they often don’t diffuse into the brickwork in high humidity levels ( i.e. when the wall is wet) and even after 2 or 3 months the gel or cream may still not have penetrated into the brickwork which reduce their damp-proofing effect.
Prior to opting for silane diffusion via cream injection Peter Cox had a transfusion system of installing a chemical damp-proof course whereby the siliconate damp-proofing fluid was gravity-fed through bottles and tubes placed in drill holes. The damp-proofing fluid would then diffuse slowly into the wall and saturate the brickwork filling voids and pores whilst avoiding the viscous fingering which occurs with pressure injected damp-proof systems. Currently there is only one transfusion damp-proofing system available in the UK and this is a frozen damp-proof course known as Freezteq whereby frozen sticks of damp-proofing fluid are inserted into pre-drilled holes. The ice sticks then melt gradually and the damp-proofing fluid spreads gradually across the brickwork and provides and effective damp-proof barrier. The only drawback is that it can be a time consuming process as after the first set of sticks has melted the process has to be repeated 2 or three times in order to form an effective damp-proof course. But according to I'Anson & Hoff the correct installation of a pressure-injected damp-proof course would also be time consuming and the Freezteq damp-proofing system is acknowledged by most scientists in the remedial treatments industry as being the most effective form of retro-fit damp-proofing available today.
There is also another transfusion type damp-proofing system marketed by Koster Waterproofing which involves the drilling of holes and then injecting a damp-proofing resin which as well as being hydrophobic ( i.e water repellent ) is also a pore blocker and has proven to be very effective in preventing rising damp. However it can be time consuming as the injection/ diffusion process can take up to 48 hours and is more complicated than any other injected damp-proofing system and the whole process involves using resin cartridges, suction angle units and capillary tubes for each drilled hole but the manufacturers are very confident about it’s effectiveness in controlling rising damp. For further information contact Koster Aquatechnic in Dumfries on 01387 270252 or www.kosterwaterproofing.co.uk
EVAPORATIVE DAMP-PROOF COURSES
Believed to be used as long ago as the 1930s when the Knapen tube system was used at the Palace of Versailles and later patented by Royal Doulton after they found that their ceramic tubes appeared to attract and absorb moisture. These tubes were heavily marketed in the 1960’s and 70’s but fell out of favour with the public with the advent of chemical damp-proofing which could be done at roughly half the cost. Currently this form of damp-proofing is only undertaking by one company in the UK (Hydrotek Wallguard) but their website does not give a comprehensive explanation of how this damp-proofing system works.
There is no independent scientific evidence to show that this form of damp-proofing reduces rising damp but there does seem to be some evaporative effect just above ground level which can lead to a slight reduction in rising damp internally and allow re-decoration without the need for re-plastering.
A more elaborate system has been developed by Schrijver Damp Control and Holland Damp Proofing both which are designed to induce air-flow, condensation and moisture removal but they seem to be dependent on local wind and weather conditions, i.e. it depends on which way the wind blows . Research by the Independent Dutch Laboratory, TNO (Organisation for Applied Scientific Research) states that the performance of these damp-proofing tubes is governed by external environmental factors such as wind speed, wind direction, temperature and relative humidity and neither the Wallguard, Schrijver or similar systems of rising damp control have been awarded with a British Board of Agrément Certificate (BBA).
These much maligned damp-proofing systems do have some evaporative effect and will help walls dry out but so would the drilling of any 50mm diameter holes at the base of damp walls and if you are considering using this form of damp-proofing 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 when the same affect could be achieved at a fraction of the cost by installing extra air bricks or vents.
The picture on the left shows a semi-detached house in Malvern, Worcestershire, the row of inserts at the base of the wall are intended to stop rising damp but this treatment was probably not needed as the house was built around 1930 and will have a functioning physical damp-proof course at the base of all the ground floor walls. The row of tubes on the first floor were probably to control condensation dampness but this could have been achieved easier and cheaper by the installation of two or three passive dehumidifiers. The row of inserts on the ground floor are about 300mm above the base of the front door and therefore even if this Dutch damp-proofing system is effective then rising dampness will still be affecting the wall up to the height of the vents which will result in dampness in plaster and also possible decay in skirting and other timbers abutting the ‘damp’ wall.
The photograph on the right is a terraced house in Sandycombe Road, Kew, Richmond TW9 3SU with the damp-proofing works being carried out at first floor level. Is this to stop rising damp or condensation dampness?
Electro Osmosis as a form of damp-proofing 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 scientifically unproven and it is also 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.
The Building Research Establishment has investigated electro-osmotic damp-proofing and it has some reservations about its effectiveness in controlling rising damp and this form of damp-proofing has never been awarded a British Board of Agrément Certificate (BBA).
PHYSICAL DAMP COURSING
The Building Research Establishment, in its Digest 245, confirms that a physical damp-proof course 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.
Diamond tipped angel grinders are 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.
The lifespan of a physical damp course is far longer than any chemical damp-proofing and it creates a total barrier against rising damp.
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 damp-proof membrane 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.