The Case of the Floor/Wall Junction
An old solid walled brick built barn had been converted into a swimming pool. Walls had been injected with a Damp wallchemical 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 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. Eruption of finish
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 Moisture profileand 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.
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.
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