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Damp is a very complex subject; it is probably one of the most difficult things to correctly diagnose. Damp has so many variables that an immediate diagnosis is in my opinion not possible. If someone comes to your property, waves a resistance meter (battery powered meter with flashy lights and or a beeper) across your wall then shouts out a price – chase him or her away because they do not know what they are doing. It will take time to correctly go through the observations required to make any sort of remotely correct diagnosis. Too often have I visited a property to be told that the company before me, were only there 15 minutes and that included the survey, diagnosis and quotation. In order to correctly identify a damp problem, you need to start with an external survey checking all possible sources of water ingress this will include checking for:-

Existing damp proof course
Condition of roof covering and flashing's/chimneys
Condition/function of rainwater goods
Condition of windows and seals to brickwork etc
Condition of pointing
Condition/type of mortar used in construction
Have properties to either side been injected
Is there any bridging from planters, flower beds etc
Is there any staining or obvious signs of water leakage on the walls
Is there any signs of problems with underground pipe work
Are the rainwater gully's blocked or incorrectly configured
Do the downpipes/hopper heads spew water down the elevations
Have the downpipes (if cast iron) corroded through at the back where they do not get painted
Are the bay windows discharging correctly
Are there any ground level irregularities (is the internal floor lower than the external ground)
Are the external paths/driveways falling away from the property, or are they pooling and/or running against the property walls.
Is the ground water channeled away from the building effectively.
How many and what size are the installed airbricks (if any)
How are the airbricks positioned

Having run through all of this with a full unhindered view of all these areas you should then move inside the property, it is important that (if the floor is of timber construction) floorboards are lifted to check for water on the sub floor oversite, too many times have I found a deep pool of water under the boards from a plumbing leak. At this time the timbers adjacent to any damp wall should be checked for rot, a reading of the moisture content of the floor timbers should be obtained, this will confirm the level of risk to the floor timbers and whether or not there is adequate ventilation.
On the internal walls you should look for any embedded pipework, copper pipes often pass unprotected through walls. The copper reacts with the building materials forming a patina (green rot) on the copper, eventually a pinhole can appear in the copper (often in the middle of the wall) and the pipe can discharge within the wall, this can create mild to heavy damp across a wide area or a severe problem locally around the pipe.

Another fallacy is that rising damp will only go 1 metre up a wall, this is absolute rubbish and the height reached depends on several factors, the main factor being the thickness and construction of the wall, if you consider that the volume of damp entering a wall will be determined by the materials used in construction (porosity) and the footprint of the wall, once the damp is within the wall it will evaporate out of the wall surfaces, if the wall is 600m thick (stone walls for example) the volume of water within a given section of that wall (say a 1square metre section) will be greater than the volume in the same section of a 300mm thick wall (solid brick for example). Both these walls will have the same surface area (2m2) so if water evaporates from the wall at the same rate it will take twice as long for a given volume to evaporate from the stone wall. In my experience the stone wall will evaporate over a greater area and will inevitably give a damp reading higher up the wall, I have seen internal stone walls with damp readings at 2.2 metres. (I have greatly simplified this for ease of explanation, there are various other contributing factors to be considered.)

Contractors often recommend an injection system and re-plastering regardless of the actual requirements, the reason for this is that the re-plastering will in itself hide the problem, but not necessarily cure it. If correctly specified and formulated plasterwork is applied, the damp will not show on the interior, salts will not manifest themselves on the internal wall surface, and to all intents and purposes the problem will temporarily appear to be cured. The problem has probably been hidden, not cured, in fact the problem will probably develop a different set of symptoms over time. More often than not there is a combination of factors causing the reported problem (see list above). If all of these factors are not corrected damp may remain in the walls, if this occurs the wall will be cold, there is then a high risk of condensation, this can lead to black spot moulds appearing on the surface of the wall. This occurs when the humid air within the property finds a cold area and changes back to its liquid form creating anything from a damp surface to water trickling down the walls (see condensation).
Damp is a horrible thing, it can at worst cause anything from health problems for the occupants to severe building degradation. At best it can raise your heating bills.

Owing to the complexity of the subject and the number of variables involved I would recommend calling in an expert to sort out this particular problem. Now you have an idea of what is involved watch the surveyor and see just how in depth a look they take, If they do not inspect the items outlined above, ask him or her as to how they have reached their conclusion, they will probably tell you ‘from experience’.

If you would like me to arrange a free, no obligation report click for a Free Inspection.

If you have any questions please feel free to email me I am always happy to help