Monitoring moisture condition case studies

The drying contractor monitored the drying of a property in Tenterden by continually checking moisture meter readings on walls, in woodwork and on the floor, making best use of the pin probes and capacitance function. The dehumidifier was watched closely and the water collected was recorded. Air was monitored too, both room air and the trapped air within holes drilled in the walls.

It was interesting to use a capacitance meter over the ground floor screed to see what readings might be during the first site survey, when the kitchen area was clearly wet from a plumbing leak. Usefully, much of the remainder of the house floor had not been affected – a control ‘dry zone’. Readings using ‘search mode’ were made methodically on this first inspection day. And later, when the floor was considered by the contractor to be close to being dry, again search mode readings were taken over the whole floor zone. (Note: a ‘search mode’ reading is terminology of one manufacturer and refers to a moisture meter reading with the instrument switched to capacitance mode.)

Figure 1: 19 July 2003, search mode readings - floor. Very high (maximum) search mode readings were obtained in the kitchen area - the seat of a leak. Dry zone readings were 170. Readings all over the floor would be expected to gravitate to 170 as it dried

Figure 2: 3 October 2003, search mode readings - floor. The wet floor zone is now certainly much drier. Search mode readings over the whole floor area would be likely to equate to dry zone readings of 170 eventually - so a little more drying is needed here. Checks by humidity box or by taking drilled samples for carbide test would clarify the floor moisture condition beyond doubt

You can appreciate that between July and October there was a significant change in capacitance readings taken over the floor screed – as if a plug had been pulled out in the centre of the property. The place where high capacitance readings persisted would probably be the lowest point on the concrete slab.

You cannot be convinced by capacitance meter readings alone that a screed has dried enough for drying equipment to be switched off and wheeled or carried out, but it is a useful piece of evidence. It certainly shows you where the screed may still be a little damp. You would feel happier if the whole floor produced readings around 170 - the level of reading in the dry zone. A reading of 200 means the screed may still be a significantly damp and this is a 1970s chalet bungalow with almost certainly a plastic floor membrane. In an old property without a proper concrete slab you would find that even after rigorous drying the screed is still ‘damp’ and will never become ‘dry’.