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Posted by: on 08/11/2016
Over the years I have attended many commercial or public buildings where they are experiencing 'Rising Damp' problems. I discovered early on that Rising Damp is not always the cause of the damp.
I learned the hard way. As a contractor, we carried out remedial work on a school in the main hall. The building was approximately 40 years old. Everything told me that it was too modern to be affected by rising damp as it would have had a dpc installed at the time of construction. There again it was built during a building boom and it was possible that the dpc had been omitted.
The pattern of damp staining was very suggestive of rising damp. The presence of high salt contamination suggested rising damp as the wall plaster tested positive when tested for chlorides. Chlorides, as well as Nitrates, are very common when ground water migrates through a structure.
To cut a long story short we treated it as a rising damp scenario. Exactly 1 year later I had to revisit the school as the same problem had re-occurred. The penny dropped.
I visited the cleaning store cupboard and asked to see what products were used during the cleaning process. I took away a sample of the product and had the product and the wall plaster analysed. The test revealed that the source of the damp was high levels of chlorides stemming from the cleaning product. The product contained chlorides which are 'Hygroscopic' (they will absorb atmospheric moisture).
The cleaners would use a mop when cleaning the floor and the skirting boards. Over the years the wall plaster had become loaded with chlorides (which readily absorb moisture from the atmosphere) to the point where the wall plaster became damp stained. This occurs due to a process known as 'Deliquescence'. The salts absorb moisture to the point of saturation and in turn, revert back into liquid form. The pattern of the damp staining is very predictable, normally 50-100mm above the skirting board and uniform throughout the area.
Moisture traps used for keeping cupboards dry rely on the same principal. You put your moisture trap (full of crystals) into the cupboard and weeks later you have a tray full of water and no crystals.
I have found this defect to be very common in public buildings such as swimming pools and hospitals, where hard floors are cleaned using lots of water and cleaning agents. Once identified the remedial work is not as extensive as new dpc installation. There is no need for a damp proof course and the amount of specialist plastering needed is minimal. There are easy solutions for preventing future contamination too.
As they say, you live and learn.