Damp diagnosis and repair
We were recently instructed by a shop fitting outfit currently working on a large commercial refurbishment project on High Ouse gate York for clothing chain Urban Outfitters, to investigate problems of damp within the basement walls and provide a repair solution.
The basement has front and rear walls which are fully below ground level and earth retaining therefore subjective to the lateral penetration of damp moving through the walls and potentially hydrostatic pressure built up from bearing ground water upon the walls. The party walls however, are not earth retaining as there divide neighbouring buildings which also benefit from basement rooms therefore, they are only susceptible to rising damp, moisture wicking through the structure where in contact with the ground.
During our investigations we were unable to find the presence of a horizontal damp proof course within the walls which was expected as the property predates 1875 when damp proof course were formally introduced under the Public Health Act. The absence of such protection would mean the walls are potentially at risk from rising damp.
Profiling of the walls was undertaken using a specialist calcium carbide meter. A calcium carbide meter is a specialist piece of measurement equipment used to measure and determine the presence of moisture within a material. A series a mortar samples were removed from the wall at 200mm intervals extending from the ground upwards allowing us to measure the pattern of moisture distributed through the wall.
A calcium carbide meter is used by adding a weighed sample of the material in a flask sealed with calcium carbide. The moisture present within the material reacts with the calcium carbide producing acetylene gas which is released in quantities which are proportionate to the amount of moisture present within the material. It is the measurement of acetylene gas that provides us with the results.
Every material has a natural moisture content, this is known as hygroscopic moisture which is the amount of moisture present within the material when in equilibrium with the air under normal atmospheric conditions, caused by the materials ability to absorb moisture from the atmosphere. In addition, porous building materials such as; bricks and plaster incorporate networks of tiny pores/capillaries which are voids of empty space. These empty voids allow the material to take up additional moisture known as free moisture, which can be absorbed by the material from other sources, such as ground water during rising damp.
Although a calcium carbide meter cannot distinguish between free moisture and hygroscopic moisture, it does allow very accurate onsite measurements, which are more reliable than readings taken from an electronic moisture meter which can be influenced by conductive materials. Care should however be taken and test samples should ideally be accompanied by salt analysis tests to determine the presence of hygroscopic ground water salts which will also contribute to the results.
By knowing the natural hygroscopic moisture content of the material we are testing we can however deduce that additional moisture has been added to the sample in the form of free capillary moisture and/or hygroscopic salt contamination.
The results of our profile test were as follows;;
Ground floor level;
200mm high – 10% Mc (Moisture Content)
400mm high – 9% Mc
600mm high – 5% Mc
800mm high 3.8% Mc
1 meter high – 2.5% Mc
1.2 meter high – 1.5% Mc
1.5 meters high – 1.5% Mc 
The results from our test clearly shown high levels of moisture towards the base of the wall which diminishes as we move upwards, a profile indicative of moisture moving from the ground upwards “rising damp”. As the readings reduce the wall becomes drier and the remaining moisture left within the wall moves closer to the materials hygroscopic moisture content (air equilibrium moisture content). The hygroscopic moisture content can be determined by taking samples of the same mortar else where within the building which are unaffected by rising damp and hygroscopic salts. Alternatively a kiln dry method of weighing the material before and after drying can be used however, this is not an onsite method of investigation.
Our findings and results were reported back to our client in a detailed edited report, which included various alternative repairs. The specification for repairs differed between the party walls and the front and rear walls as the cause of dampness changed due to front and rear of the building being partly earth retaining.
Our client chose to install a diffusing water repellent cream into the party walls a horizontal barrier against the effects of rising damp. In simple terms, the cream works by diffusing through the mortar joint lining the capillary pores with a silane/siloxane emulsion which reduces attraction of water molecules to the capillary sides thus reducing the effect of wicking moisture (rising damp).
Our recommendations were to use Dryzone a cream produced by Safeguard Europe one of the leading industry manufactures of damp proofing products. Dryzone damp-proofing cream has been formulated to contain a high concentration of active ingredient (over 60% silicone in the form of active silanes/siloxanes). This makes Dryzone over four times stronger than typical competing products which contain as little as 10 or 15% silicone.
see the dryzone video here http://www.youtube.com/watch?v=jCWZBtbs0DU&feature=plcp&context=C470853cVDvjVQa1PpcFNgAtamQcSOqVvhVJyLPTSW46G5WGvT__A%3D
The damp proof course installation has been undertaken with minimal fuss, using a low hazard, non-caustic, non-flammable and solvent-free formulation which is not injected under pressure providing a highly effective solution to rising damp within the party walls.
When in need of expert advice for damp diagnosis and repair don’t hesitate to ask, call “Yorkshires Leading Damp & Timber Specialists” Dryfix Preservation Ltd
Many thanks
Russell Rafton
C.S.R.T / I.S.S.E
Dryfix Preservation Surveyor
