Originally known as Knapen Tubes then Doulton Wallguard. This method uses porous ceramic tubes fitted into walls affected by damp. The explanation that the manufacturer as to how these tubes work is that the ceramic material has good suction properties and this draws water from the from the wall fabric into the inner part of the tube and the moisture drawn in though the tube then evaporates from the inner surfaces of the tube into the atmosphere as the relatively dense humid air flowing out of the tubes and therefore inducing a ventilation process which encourages drying.
To work properly the tubes must discharge externally so they can only be of any use on the outside walls of houses, if they were used on internal walls the moisture would be released internally and this would increase humidity levels and possibly cause condensation dampness.
When properly installed the porous tube system can greatly increase the rate of evaporation from damp walls but this can also lead to salt deposits in the tubes which reduce their effectiveness as the hygroscopic nature of these salts will tend to reduce evaporation and the tubes should be cleaned or replace every five years or so. The tubes also only cause drying in a localized area around each tube and unless the tubes are close enough together then there is the possibility that there are still paths for rising dampness to occur between the tubes.
While there is no independent scientific evidence to show that Atmospheric Tube 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 which may allow re-decoration without the need for re-plastering.
Currently there is only one company actively promoting the use of ceramic tubes as a form of controlling rising damp and they are Hydrotek-Wallguard based in Ongar,Essex. Even on their website there is no satisfactory explanation of how the system works and under the ‘How it Works’ heading the explanation giving is ‘Dries out existing rising damp-Prevents future rising damp. Specially developed Hydrotek-Wallguard porous ceramic tubes work by "soaking up" water from the surrounding brickwork and mortar course.’ That’s it!
A newer system has been developed by Schrijver Damp Control which is called the Schrijver Systeem, which is a Dutch invention named after the inventor- Frank Schrijver.This system is designed to induce air-flow, condensation and moisture removal, much the same as the Wallguard Damp Proofing system, where airflow is induced within the pots encouraging condensation of surrounding damp which is then sucked out by externally but the whole system seems to be dependent on local wind and weather conditions, i.e. it depends on which way the wind blows. Research undertaken by the Independent Dutch Laboratory, TNO (Organisation for Applied Scientific Research) regarding the effectiveness of this system in controlling rising dampness 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.
There is a very similar system to Schrijver also on the market which is sold by Holland Damp-Proofing and both systems are both marketed stressing that internal plastering is avoided although if rising dampness has occurred then there will be deposits of hygroscopic salts within the plaster which will need to be removed.
The increased evaporation of Schrijver Damp Control and Holland Damp-proofing systems could lead to the build up of hygroscopic salts within their evaporative brick units which will tend to reduce their evaporation rates and also reduce their effectiveness in controlling rising dampness but nonetheless the idea of promoting chemical free damp-proofing by increasing evaporation rates from damp walls is a good one however neither the Hydrotek Wallguard, Schrijver or Holland Damp-proofing systems of rising damp control have been awarded with a British Board of Agrément Certificate (BBA) and subsequently their guarantees may not always be accepted by mortgage providers.
If you are considering using the Schrijver Damp Control or Holland Damp-proofing systems then you should have a 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. 
If you need any more information about the effectiveness and suitability of evaporative damp-proofing systems then please call us on 020 8226 3101 or e-mail