Your Questions Answered An opinion on environmentally driven damp-proofing systems.
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An opinion on environmentally driven damp-proofing systems.
This article was forwarded to us and we understand many others. Its author clearly has an understanding of damp related problems in properties. We felt that the opinions expressed in the article would be of interest to anyone considering the environmental control of a damp problem and help in the decision process of whether or not such a system would be suitable.
AN ENVIRONMENTALLY DRIVEN DAMP-PROOFING SYSTEM
- FACT OR FICTION?
- FACT OR FICTION?
In recent years there has been some significant advertising in the national press about a patented, revolutionary damp proofing system developed in Holland. Advertisements claim that it will effectively cure rising damp, condensation and penetrating damp. Furthermore they claim it to be different from other traditional ways of treating damp because there is no need to redecorate or re-plaster.
The website for the system describes it as, "-- a humidity regulated system which consists of a stone element and a ceramic tube. The whole system has fixed it in a specially prepared niche in the outside wall. Through an opening in the element, dry air can flow into the system. This is led directly in to the ceramic tube and two air chambers. The second opening in the system causes a draft. This leads to a drop in temperature within the tube and as a result a cold bridge is created. Since humidity tends to form at the coldest spot, it will gather in the ceramic tube from where it is transported out side by the air flow. In the same way, condensation from within the house also disappears."
They even further claim, “A guarantee for a dry indoor climate”
So are these claims really valid or questionable?
Installation:
It is claimed that the system does not involve complicated construction work. However, it does involve removing bricks at around every one and a half foot of wall run. The photographs supplied on the website suggest that there is a stretcher between each of the special elements. This clearly involves significantly more work than simple drilling injection holes into mortar beds. Furthermore, the system can, depending on opinion, look rather unsightly, especially where it has been installed at first floor level! Note that it also stands proud of the wall which must lend itself to damage if set along by a path - it may also ‘damage’ passers by where there is public access should they brush into the protruding units!
Performance:
Rising damp:
The material of the units must be permeable for water to pass into them. Effectively the material must emulate the old ceramic porous pots, a damp-proofing system now widely discredited. Indeed, as far back as 1930 the UK’s Building Research Establishment reported the results of their investigation into porous tubes as, “Results indicate that no useful increase in the rate of evaporation of moisture results from the use of these tubes”; this was the result of both laboratory and field testing. One of the problems they suffered from was that the permeable structure became blocked with salts as water evaporated from the porous material; this significantly affected their performance. It therefore appears highly probable that the same will occur with the Dutch units, ie, the performance drops with age.
Like the old porous pots, the Dutch system is effectively an 'atmospheric' system whose performance will be totally governed by factors such as wind speed, wind direction, temperature and especially humidity. Indeed, the website clearly states, "The amount of damp that is withdrawn depends on weather conditions and wind speed"
Looking at the units there must clearly be an optimum angle at which the wind must pass over them to perform as claimed; either side of the optimum then the wind speed through the unit will decline, the performance drop and less water will be extracted from the wall. Thus in order to be effective, air must pass through the ceramic tube at a suitable speed, preferably continuously. And, of course, the tunnel in the unit must be clear and remain clear of dirt and debris, aestivating snails, and the like, and remain free from the build up of salts.
Given a property can have four sides, only two are likely to be exposed to the wind at any one time, at least two will be sheltered. Also consider that the wind direction in the UK is predominantly SW so that only part of the property will be potentially regularly exposed to wind. Indeed, many properties are well sheltered on all four sides in their own right especially at ground level. At best winds will be well restricted to some of the surfaces throughout the year - at worst restricted to nearly all. And there are days, not infrequently, when there is no effective wind occurring. Also at night, and frequently during the day the relative humidity is often very high and, of course, the cold foggy days.
The external environmental conditions in the UK are such that conditions for optimum performance of the system are rarely reached, let alone maintained, on one wall and certainly not on the potential of all 4 walls. As such it becomes readily evident that the performance of the system as a whole is likely be extremely limited in practical situations. And it can’t be used on internal walls.
Evaporation of water from a surface is markedly dependant on the relative humidity of the surrounding air; thus the relative humidity of the external air will also have a dramatic effect on performance. At night for example the relative humidity will regularly rise to an excess of 90% (at the time of writing it was 88% at a wind speed of 4 mph) and wind speeds will be very limited even during the day on leeward and protected walls. Indeed, over the last week prior to preparing this article, the relative humidity has not dropped below 90% - just look at how long the water on the grass remains at this time of year, and consider still, foggy days. Therefore, one must seriously question the real world performance of the system when fully installed. Add to this the likelihood of salts slowly blocking the evaporative surface in the tunnel of the units then we may be looking at a very erratic, inefficient water control system, especially in the longer term.
The units appear to be of a fixed size. Therefore at a rate of insertion described and given suitable continuous conditions they should have a better performance in a 115 mm external(!!!) wall than a 450 mm rubble filled wall. Indeed, given their reported mode of action they are unlikely to have any significant effect on such thick walls even under continuous ideal conditions At best they may only cause very localised drying around the unit assuming reasonable wind speeds at the right angle and at sufficiently low relative humidity. If such conditions do not exist for any length of time (most likely) then their performance is likely to be curtailed. It must clearly take some vivid imagination to visualise water passing across the width of large proportioned solid walls from the interior facing surface to the outside element without it continuing on its passage upward - this would be required if it were to stop rising damp. For the element to work as suggested it would effectively require all pores in the masonry to pass to the unit to direct all rising water to that unit, and none to pass vertically. This would clearly never be the case.
The system claims that humidity (?) tends to form at a cold spot. It is certainly not clear what is meant by this statement. It could mean that the relative humidity rises around colder areas - if this is the case then it has nothing to do with the actual amount of water vapour in the air. Indeed, under normal field conditions experienced in the UK it is unlikely that any significant cooling occurs in the tunnel, and if it did it would readily dissipate as the result of the relatively massive thermal reservoir of bricks/stone surrounding the unit. And cooling would only occur if a suitable air flow was maintained continually through the unit; in a real world situation in the UK this would be unlikely. The venturi effect within the tube is very likely to be minimal given the natural pressure of air entering the unit. Thus any effect is likely to be minimal under practical UK conditions. If, however, they are claiming that moisture is 'attracted' to the cold spot then this is nonsense!
Test data published on their website appears to be the result of a perfect laboratory test situation - wind speed, direction and humidity are not given. Under perfect laboratory conditions it is very likely that the units remove more water from a treated wall than a standard wall. Whether this is sufficient to significantly control the dampness is not actually stated. At best water is likely to pass above the installed system especially when considering the size and depth to which the elements are installed.
Advertisements for the system also claim there is no need to re-plaster or decorate in the case of rising damp. A property that has been subject to a long term rising damp complex may well have decorative spoiling; this is irreversible. Therefore redecoration/replastering will be necessary and this is likely to incur an expense possibly well beyond the price of the insertion of the units. Furthermore if hygroscopic salt contaminated plasterwork is left (1) it may remain visibly damp due to the hygroscopic nature of the contamination, and (2) application of certain decorative finishes over salt contaminated material can become damaged. Thus the advice given in the advertisements could be seriously misleading and lead to significant further expense beyond the installation of the units.
Penetrating damp:
With reference to penetrating damp, again the units used to control/prevent this clearly must be considered with a great deal of scepticism because such simple units placed at the base a wall, or anywhere else for that matter (they have been seen at first floor level), will not extract penetrating water any distance away from these units. Again it would require all pore structures to lead to the units, and this obviously does not happen when one considers the large areas of walls in comparison to the size and location of the installed units.
Also for water penetration to cause a problem the volume of water entering must be greater than any drying/evaporation - hence it penetrates sufficiently to cause the problem. Imagine the volume of water hitting a wall from wind driven heavy rain. It is therefore simply ludicrous to expect the units to evaporate off penetrating water faster than it can enter a wall, and also prevent/eliminate water penetrating any distance above or below the units; they would have to do this before water reached to sufficient depth to cause the problem.
Furthermore, penetrating damp frequently enters via cracks, not simple fine capillaries, and will readily follow these defects in which case the units will have no effect unless the cracks lead directly to them, but water entry via this mechanism will be far greater than the units can possibly evaporate before it penetrates. Again the claim relating to water penetration is extremely exaggerated to say the least and common sense would dictate that it can't possibly be effective.
Surface condensation:
Perhaps the most significant claim is, "-in the same way condensation from within the house also disappears." Indeed, the front page of the website claims, “A guarantee for a dry indoor climate” So what about this claim?
In essence surface condensation is the result of warm moisture laden air coming into contact with a cold surface; water droplets and/or mould growth will often develop.
Over most of the year there is more water vapour within the property than outside. By far the greatest proportion of water vapour in a building is the result of 'lifestyle', ie normal living activities such as cooking, washing, breathing, etc. Indeed, the average individual is considered to produce around 10 litres of water vapour per day. The amount of water vapour produced from a damp floor (or wall) is absolutely minimal compared with the 'lifestyle' water production, and effectively makes no impact on internal water vapour levels (See note 1 below)
Water vapour exerts a pressure, the more water vapour the greater the pressure. As there is more water vapour internally than externally, water vapour moves down its pressure gradient, ie, from inside to outside of a building. Thus, water vapour is circulating within a property coming into contact with internal faces of walls and also continually moving out of the building through cracks, crevices, windows, and even through the building fabric itself. Thus moisture in the air will continuously contact the inner surfaces of walls, and also on its way out of the building through walls water vapour will also first come into contact with the inner surface of the wall and then slowly pass through the structure to the outside. If the inner surface is sufficiently cold then condensation and mould growth will occur.
The question then is how do these units prevent condensation as claimed? They are situated on the outside of the wall and as such they will afford no influence whatsoever on internal moisture production. Furthermore, water vapour will obviously come into contact with the inner surface of the wall before it continues through the structure. So at what stage in this pathway is it claimed that the units remove water vapour to prevent condensation? Clearly they do not! Water vapour contacts the inner wall surfaces where surface condensation occurs before it reaches the units fixed into the outer part of the structure; therefore the system cannot play any part whatsoever in the control of surface condensation or water vapour within a property.
Furthermore, there is a temperature gradient through the wall, in the colder months it would be expected to be colder on the outside through to warmer on the inside. If the system works as claimed causing a drop in temperature in the unit, then clearly during the colder months this will lower the temperature of the wall even further along the line of the installed units. Also any air entering the tunnel in the unit is likely to be colder than the wall. Because the units are embedded in the wall, these two factors theoretically move the ‘coldness’ closer to the internal face of the wall with the result that the installation of the units is far more likely to lower the internal face temperature further to cause/exacerbate condensation around the line of the units in the wall rather than cure it!
The claim relating to the disappearance of condensation within the house can only be described as nonsense and clearly shows a fundamental lack of understanding regarding moisture production and vapour movement in the domestic property. So the claim that, “A guarantee for a dry indoor climate” must be considered significantly flawed!
Summary:
Given ideal laboratory conditions including a suitable warm wind at constant suitable high speed at a sufficiently low relative humidity flowing over the units at an optimum angle, more water may be expected to be removed from a treated wall than untreated. This is probably more likely to be due to the increased surface area effected by the tunnel in the unit rather than any other affect. But whatever the case given a typical damp, humid cold day, little wind and certainly not passing around all sides of the building, and changeable wind direction and speed then it is evident that the performance of the system will be significantly degraded, probably at times to be almost totally ineffective. As stated on their website, “The amount of damp that is withdrawn depends on weather conditions and wind speed". What they don’t tell you is how their tests relate to site conditions in the UK. Thus the system is totally at the mercy of the environment which will be almost certainly different from any laboratory tests the system has been subjected to.
Thus overall it is very clear that the system is totally governed by external atmospheric conditions and in practice these are highly unlikely to be ‘optimal’ for suitable performance to eliminate or substantially control rising or penetrating damp. It will have no effect upon or ‘repair’ existing damaged or salt contaminated plaster/decorations as a result of rising damp; the frequently essential replacement of damaged decorations and contaminated plasterwork will incur further costs if a dry, non-spoiling decorative surface is required.
And for “A guarantee for a dry indoor climate” - hmmmm!
[Note 1. The origin of the water contributing to a condensation problem within a building is almost always from ‘occupancy activities’, ie, cooking, washing, breathing, lack of ventilation, intermittent or inadequate heating, etc. Moisture in damp walls, floors, etc, is not considered to be a significant contributory factor to the internal atmospheric water burden of a property because the water vapour arising from such sources is usually insignificant in comparison to that arising from normal household activities. Indeed, research undertaken at Building Research Establishment, East Kilbride (C.H.Sanders - unpublished data - 6/2/01; and now published in ‘Understanding Dampness’ BRE Publication 2004) showed that the amount of water lost from a saturated floor slab was around 36g per day for a floor area of 8 m2. This would compare with 10,000g per day produced by a single individual undertaking normal household activities, eg, cooking, breathing, bathing, washing, etc: damp walls should behave no differently. Thus water vapour losses from capillary bound water in walls is therefore of little significance, and even less where dense renders, paint films and vinyl based wallpapers further reduce evaporation. Water from such sources therefore adds a negligible amount to the overall internal moisture burden of the property; in practical terms it can be discounted.]
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