Plaster Properties - Effect of Plaster-Water Ratio

Plaster-water ratio (by weight) of 100 plaster to 30 water gives:
a setting time of 1.75 mins,
a compression strength of 813 kg/sq cm., and
a density of 1806 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 40 water gives
a setting time of 3.25 mins,
a compression strength of 477 kg/sq cm., and
a density of 1548 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 50 water gives
a setting time of 5.25 mins,
a compression strength of 318 kg/sq cm., and
a density of 1352 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 60 water gives
a setting time of 7.24 mins,
a compression strength of 230kg/sq cm., and
a density of 1207 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 70 water gives
a setting time of 8.75 mins,
a compression strength of 176 kg/sq cm., and
a density of 1083 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 80 water gives
a setting time of 10.5 mins,
a compression strength of 127 kg/sq cm., and
a density of 990 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 90 water gives
a setting time of 12 mins,
a compression strength of 99 kg/sq cm., and
a density of 908 kg/cubic metre

Plaster-water ratio (by weight) of 100 plaster to 100 water gives
a setting time of 13.75 mins,
a compression strength of 70 kg/sq cm., and
a density of 867 kg/cubic metre

Properties of Typical Gypsum Plasters and Cements

No. 1 pottery plaster
Water to be added as % of dry mix by weight - 70%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1106
% expansion on setting - 0.21
Compressive strength (kg/sq cm) - 127.26


No. 1 molding plaster
Water to be added as % of dry mix by weight - 70%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1106
% expansion on setting - 0.20
Compressive strength (kg/sq cm) - 141

Plaster of Paris
Water to be added as % of dry mix by weight - 70%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1106
% expansion on setting - 0.20
Compressive strength (kg/sq cm) - 141

No. 1 Casting plaster
Water to be added as % of dry mix by weight - 65%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1162
% expansion on setting - 0.22
Compressive strength (kg/sq cm) - 170

Pottery plaster
Water to be added as % of dry mix by weight - 74%
Setting time - 27-37 mins
Dry density (kg/cubic metre) - 1057
% expansion on setting - 0.19
Compressive strength (kg/sq cm) - 127

Hydrocal cement
Water to be added as % of dry mix by weight - 45%
Setting time - 25-35 mins
Dry density (kg/cubic metre) - 1442
% expansion on setting - 0.39
Compressive strength (kg/sq cm) - 35

Hydroperm cement
Water to be added as % of dry mix by weight - 10%
Setting time - 12-19 mins
Dry density (kg/cubic metre) - <641
% expansion on setting - 0.14
Compressive strength (kg/sq cm) -


Hydro-Stone cement
Water to be added as % of dry mix by weight - 32%
Setting time - 17-20 mins
Dry density (kg/cubic metre) - 1914
% expansion on setting - 0.24
Compressive strength (kg/sq cm) - 707

Ultracal cement (30)
Water to be added as % of dry mix by weight - 38%
Setting time - 25-35 mins
Dry density (kg/cubic metre) - 1588
% expansion on setting - 0.08
Compressive strength (kg/sq cm) - 424