The Case of the
Floor/Wall Junction
Background:
An old solid walled brick built barn had been converted into a
swimming pool. Walls had been injected with a
chemical
damp-proof course and lined using polypropylene membrane; this membrane had
been linked with similar membrane beneath the floor screed. Walls were rendered
using a proprietary permeable pre-mixed gypsum based one coat plaster.
Shortly after completion of the project eruption of the finish developed around the external walls up to a height of around 750 mm: this was reported to be either a failure of the wall membrane or condensation.
The Investigation:
The hygrometric data showed all surfaces well above the dew point
temperature; condensation was not occurring and the data showed walls to be at
very low risk to surface condensation.
Moisture and soluble salt profiles showed water to be rising from
the base of the wall, but no significant levels of soluble salts or
concentration of such salts (chloride
and nitrate from long term rise
of ground water) had developed suggesting the water rise had been short term
and not due to membrane failure (i.e., diffusion of water/salts from the
underlying wall would have caused contamination).
A section of the plasterwork was removed and the floor/wall junction excavated. Examination showed the wall membrane and its junction with the floor membrane to be well formed and sealed. However, the screed (set under stone slabs) was distinctly damp and the porous plasterwork had been taken down below this screed, i.e., there was a 'bridge ' between the damp screed and plasterwork. It was also noted that water damage to the finish was to greater heights than the current height of rising water; this suggested drying down had occurred.
Conclusions:
The water causing the spoiling was not due to condensation or a failure in the polypropylene membrane system. It was the result of the structure of the floor/walk junction allowing 'water of construction' in the screed to 'bridge' into the permeable plasterwork. As the screed dried out the height of the rising water declined. The removal of the bottom of the permeable plaster coat effectively eliminated the problem.