This is part of a series of posts – find an introduction & links to the other sections of wall here.
One of the more puzzling damp walls in the house is documented below. It is an internal ‘spine’ wall, running perpendicular to the party walls, supporting the joists upstairs & some of the loading from the roof. We cannot find any obvious leak or pipes running underneath. The subfloor slopes down to the base of this wall & is lower than the subfloor at the front of the house.
The manifestations of damp here are more unusual, since it is more common for them to appear predominantly on external walls which tend to be colder, exposed to weather & have often been modified in ways that trap water. There are several theories that have been considered, but I am yet to come to any definite conclusions.
14/08/2015 ….Soon after purchasing the house. The front room is on the other side & showed signs of damp as does the section of this wall that is in the hallway. It was covered with impermeable vinyl wallpaper & slightly glossy paint to hide the problem. The skirting boards were rotten in places. We decided to strip the wallpaper & lower section of plaster off, along with the rest of the downstairs.
When initially stripping the lower section of this wall, we found the original lime plaster had been removed and replaced with gypsum up to around 1m high in a fairly straight line & there were sections of cement right at the base of the wall as well. It has been suggested to us that this is just darker in colour and not actually damp, but the mortar is dark & sticky when removed and quickly dries out in the hand to form a lighter coloured powder.
There is a section where the damp is slightly higher up towards the left side. Overall, this is a much more even distribution of damp along a wall than other areas of this room.
31/07/2017 …You can see that after 2 years of being allowed to dry out from both sides, the wall is still damp :
Tuesday 01/08/2017 …after removing the lime plaster :
05/08/2017 … 12 hours after 1st coat of limewash :
06/08/2017 …36 hours after 1st coat of limewash :
07/08/2017 …60 hours after 1st coat of limewash :
09/08/2017 …36 hours after 2nd coat of limewash :
11/08/2017 …4 days after 2nd coat of limewash :
12/08/2017 …5 days after 2nd coat of limewash :
14/08/2017 …6 days after 2nd coat of limewash :
21/08/2017 …2 weeks after 2nd coat of limewash, after returning from being away for a week :
04/09/2017 …1 month after 2nd coat of limewash :
06/09/2017 …no obvious changes :
08/09/2017 …still no change :
It has been suggested that this may be damp caused by excess humidity & condensation on this wall. I was surprised to hear this since I would have thought being an integral wall it would not have been cold enough. One idea is that underfloor through drafts could be making the base of this wall cold, or it could be the meeting of warmer air from the south facing front of the house and the cool air from the north facing rear.
An observation that could bolster this hypothesis, is that the use of a ‘moisure meter‘ does indicate that the bricks/mortar below floor level may be less damp, which would give less weight to the idea of any capillary action happening from a damp sub-floor. It is very important to consider the significant limitation of these devices. Use of these meters to measure potential damp is generally ill-advised since they do not measure moisture, just conductivity & they are only really useful for measuring the moisture content of wood, not building materials. The reason for this is that there are often contaminants such as salt, bits of metal (there are plenty of these in the mortar of this house due to it being cut with ash from blast furnaces), lead paint etc …all of which will give false high readings.
However, I have found through extensive readings from multiple different areas of the wall that I can build up a picture of what readings correlate with genuinely damp areas due to observation of other phenomena (such as the darkness of bricks/mortar, the way it dries out going paler & dusty on the skin). I can also obtain repeated lower readings along this same wall in the lighter / drier areas above the tide mark in this room. I will always take readings from these meters with a pinch of salt – the limitations of them should always be borne in mind.
I have also been utilising a handheld infrared thermometer to monitor the various temperatures in different areas of the house at different heights on the wall. As expected, the rear kitchen walls, lean-to and rear dining room walls do get very cold, but this spine wall is no colder in general than the perpendicular party walls & they are much less affected by damp (particularly the one to the east). A more accurate way to measure this would be with a thermal imaging camera, but that would not be a worthwhile investment!!
There is an extensive humidity problem in the property however & it could be that with other colder walls saturated, if the humidity ever reaches 100% it will find somewhere to drop out, and this spine wall could be the next best place after the rear external walls are saturated.
Another thing I have been contemplating, is that excessive humidity could in theory be caused by a saturated wall (for example from a leak) constantly trying to dry out, thus evaporating moisture into the internal environment which could then be re-condensing when the water vapour reaches a cool spot.
Despite all of the above, I have a intuitive feeling based upon observing other things within the house, that the root cause of the damp may be due to something other than just occupant generated humidity condensing upon walls. I am not ruling it out however – and the observation of humidity using a combined hygrometer & thermometer with multiple sensors installed wirelessly around the house is certainly incredibly enlightening.