Water-repellent treatment of plaster elements and plasterboard / wallboard.
SILRES® BS 94 is added to the mixing / gauging water of the plaster. The addition of just 0.2-0.4% SILRES® BS 94, expressed in terms of the plaster, effects a marked reduction in water absorbency as required by DIN EN 520.
The efficiency of SILRES® BS 94 depends on the kind of plaster, on the water / gypsum ratio and on additives such as starch / cellulose or surfactants. This is why no general recommendations on the dosage of SILRES® BS 94 can be given. Preliminary tests are always necessary for establishing the required amount.
Alkaline components of the plaster may lead to diminution of the bulk density and the water repellency of the plaster elements.
SILRES® BS 94 is not recommended for surface treatment of plaster elements.
Suggested formulation for laboratory tests: 1,25g of SILRES® BS 94 is mixed into 400g of deionized water with a turbine mixer (at least 1,000rpm) for 30 seconds. 500g of plaster of paris is added to this mixture. The mixture stirred with a paddle mixer for one minute and then poured into PVC rings (diameter: 8cm, height: 2cm). After setting, the samples are removed from the PVC rings and dried for 24 hours at 40°C in an exhaust hot-air cabinet with open flap. Subsequently the samples are dried for six days of room temperature during that time they will reach their constant weight.
To determine water absorbency, the samples are placed horizontally into deionized water so that they are covered by 5cm of water (DIN EN 520). After 2 hours they are taken out, the remaining drops on the surface are removed and the samples are weighed. The mean water absorbency of at least 3 samples is calculated terms of the dry weight of the plaster samples before immersion in water. Untreated samples produced by the same method have a water absorbency of about 50%.
