Damp course system

Jenny Dickens <jenny.dickens [at] doi__vic__gov__au> writes

>An "Electro Osmotic Dampcourse System" has been recommended to an
>architect colleague for use on an historic building.  According to
>data from the manufacturing company:

The traditional problem of electro osmotic damp proof systems
relates to the levels of moisture which tend to be found in historic
buildings.

The system works by drawing moisture from the anode to the cathode
(in you case from the wall back into the ground). In industrial
applications where there is a very high moisture content possibly
70-80% and the requirement is to remove 25% of the moisture, the
level of electrical resistance in the material is low and the system
tends to be successful. The problem for historic buildings is that a
wet wall might have a moisture content of only 18% (by vol), and in
order to make it 'dry' we might wish to reduce this to 5%. At these
levels the electrical resistance in the wall is very high,
significantly reducing the efficacy of the system. Also there is a
problem of diminishing returns: In other words the dryer object
gets, the harder it is for the system to work. The difficulties of
the system when applied to historic buildings are discussed in
Ippolito and Giovanni Massari, Damp Buildings Old and New, ICCROM,
1993, pp 94-97

Have you measured the moisture content in the wall (in the core
rather than at the surface)? It would be important to know the
current moisture content and the level to which you hoped to reduce
it. (Also one must not ignore the possible effects on the
surrounding building fabric, which may be caused by reducing the
moisture content at the base of the wall.)

The other problem with any active system of course is that of
maintenance and power supply. In historic buildings one is dealing
with problems over many decades if not centuries. It is obviously
important to look at the expected lifespan of any moisture control
system as well as the level of maintenance that will be required in
the very long term.

Tobit Curteis
Tobit Curteis Associates
36 Abbey Road
Cambridge CB5 8HQ
+44 1223 501958
Fax: +44 1223 304190


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                  Conservation DistList Instance 15:12
                   Distributed: Friday, July 13, 2001
                       Message Id: cdl-15-12-004
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