This unusual phenomenon is caused by patches of salt contamination in the plaster.  The salts are hygroscopic and absorb moisture from the atmosphere when the relative humidity is high.  Once the humidity returns to normal levels, the patches disappear.  This makes it difficult to spot unless the conditions are right. 

You can only make so many holes in the wall with your moisture meter before the lady of the house asks you to leave!

Client(s)   Mr & Mrs L

Property   West Yorkshire

Instructions To inspect the property and provide an opinion on dampness to the chimneybreast and one wall in the dining room.                                               

Background   The clients have lived in the house for approximately five years and it is fair to say they noticed problems on the affected walls soon after they moved in.  However, these problems, which are in the form of staining and apparent dampness to the wallpaper, have not improved, and they now require an independent assessment of the situation.

The current problems were not noticed during my clients’ pre-purchase survey, which was carried out by a chartered surveyor.

It is also worth noting that Messrs ***** (well known remedial company) carried out damp proofing works in 1985, and there is a guarantee in force for this treatment.

Disclosures   I am not aware of any affiliation, financial or otherwise, with the client or the prroperty.                                               

Limitations  Limited to the instructions.

Restrictions The survey was non-invasive.

Date of Survey   September 2008

Weather  Fine, clear.  Both this summer and the last one, in 2007, were noteworthy for excessive rainfall and continuous high relative humidities.  These latter conditions will have had a significant effect on the perceived problems.                                                

Viewing Orientation Unless otherwise stated, all observations are made as if looking towards the house from the front.

Type of Property Detached house, c1850. I believe it was created by the amalgamation of several, smaller cottages. There is central heating and [majority] sealed unit double glazing in timber frames.

External Observations There are no external observations that would affect this report.

Internal Observations These are mainly confined to the dining room, although the kitchen, which has significant relevance to this report, was also inspected.

The right-hand wall in the dining room was once probably a dividing wall between two separate cottages, and on the kitchen side of it, a stone staircase ascends to the first floor. This staircase, which originates in the entrance hall, has a storage pantry beneath. The individual steps rest in both the dividing wall in the dining room and also a further wall, which faces into the kitchen, to the right.

There are several dark stains on the surface of the dining room wall, and on at least one of these stains, surface water was present in quantities sufficient to allow it to trickle down the wall.

Similar stains were apparent to the rear side of the chimneybreast, on the opposite (left-hand) wall, between this room and the living room, although surface water was not present here.

Although moisture meter readings confirmed the areas of staining were damp, moisture content readings taken from the skirting boards indicated the timber had a moisture content of less than 12%, which is perfectly acceptable.

The double-glazed windows in this room do not have trickle vents.

The [once open] fireplace is now effectively sealed by a gas fire.

The kitchen does not have an extractor fan and relies upon the cooker hood for ventilation.  These hoods are grossly inefficient for this purpose

I am advised that connecting doors between the kitchen and other rooms are usually left open. 

Discussion  There are three types of dampness that affect houses:

                    Rising dampness, penetrating dampness & condensation.

The nature of the problems exhibited in this house effectively rules out the first two types.  Rising dampness is constant; emanates from the floor; and does not produce the isolated patches seen on these walls.     

Penetrating dampness could produce the isolated patches seen here although this would be unusual.  In addition, for dampness to penetrate into the dining room, there would need to be a source of moisture on the other side of the wall, either on the staircase itself or in the pantry beneath.  This is patently not the case.

Therefore, the only viable source of moisture for the dampness seen on the dining room wall in this property is that resulting from condensation; and this theory is given credence by the free, surface water and also by the moisture content of the timber skirting boards.  These latter are perfectly normal for a house with central heating and indicate that the problems with the walls are caused by a surface phenomenon, i.e. condensation.

The symptoms on the chimneybreast indicate this phenomenon is active here too.

That it (condensation) has taken on the appearance it has, i.e., isolated patches, is also rather unusual, and must result from areas of salt contamination in the plaster on the walls.  These salts will be hygroscopic and during periods of high relative humidity they will absorb moisture from the atmosphere.  The salts in the areas where surface water is forming will also be deliquescent, i.e. given suitable circumstances they will turn to water 

From my understanding of the situation, Messrs ***** treated these walls in 1985 and this treatment should have included re-plastering, either with a prescribed sand and cement mix or with another form of plaster that contained a salt inhibiting agent. This being the case, I would submit that it (re-plastering) has failed to meet its design functions in these areas. (There seems to be some confusion as to whether the chimneybreast was also treated by Messrs *****)

The choice you now have is to reduce the condensation to levels that no longer trigger the problem, or to ask ***** to return and re-plaster the walls.

The first option is necessary in any case; and as well as being beneficial for the property as a whole, it will also be the least disruptive; the second option will require the re-plastering of the affected sections of the walls.  In addition, there is always the possibility that in the intervening years between *****’s treatment and the present time, some other agent or person may have skimmed the walls. If this is so they (*****l) would probably try to disown any responsibility for the present travails.

After our discussions on site I would recommend that you firstly try to reduce condensation; and so that you may achieve this aim I have enclosed a small pamphlet.

In addition, I shall recommend physical methods in the next section of the report.

Conclusions The stains on the walls in the dining room result from condensation and salt contamination (salt damp).

The property generally will benefit from increased ventilation and this in itself may cure the problems.  Accordingly, you should carry out the following work:

 Install a good quality extractor fan in the kitchen.  The Ventaxia Centrif 250hp model should be suitable for this location, and on reflection, I think it could be fitted on the wall over the rear door.

You should place a ‘Perko’ door closer in the right-hand stile of the kitchen door.  This will not normally be visible but it will ensure the door is kept closed and thus any moist air, produced in the kitchen, will not be allowed to permeate throughout the rest of the property.  

 It may eventually be necessary to install trickle-vents into the top rails of the windows in the dining room.  However, I would prefer to see how effective other measures are before adopting these.

If the problem persists once we are sure the condensation issues have been addressed, it will be necessary to contact ***** to canvas their opinion.  If they decline any responsibility, or they reveal they didn’t actually treat the chimneybreast, the salt contaminated plaster will have to be replaced by others.                                           

To do this, the plaster should be replaced with a base-coat render mix of 3:1, sharp, well-graded (to BS1199) sand to cement, which can then be skimmed with a multi-coat finishing plaster.  I would expect you to contact me again should this eventually be considered necessary.

I trust the above is satisfactory for your purposes but if you require further clarification please do not hesitate to contact me.      

Date of Report                          9^th September 2008

The above findings are based partly on the interpretation of results from a standard non-destructive inspection; this, by necessity, has limitations. If you require confirmatory/definitive diagnosis of my findings then this can be undertaken by the use of destructive methods of investigation: these will involve some damage and costs.