Plaster Calculator Download
NOTES ON WORKING WITH PLASTER:
Pottery Plaster Mix For Wedging Tables:
For wedging boards or tables mix 70 parts of water to 100 parts plaster. This equals 4.17 gallons water per 50 pounds dry pottery plaster.
Product Data
– The best material available for sanitaryware and dinnerware casting.
– Formulated for long life and reduced breakage (stronger molds).
– Available with or without thermal shock additive.
#1 POTTERY PLASTER is highly uniform, noted for outstanding performance and long life. The standard of the industry - this is the best material available for sanitaryware and dinnerware casting. Used for making plaster bats, wedging boards, and working molds. This is a relatively soft plaster which may be used for carving.
Technical Properties English Metric
Use Consistency (parts of water by weight per 100 parts plaster ) 70 70
1 Hr. Compressive Strength 1,000 psi 6.8 MN/m2
Dry Compressive Strength 2,400 psi 16.3 MN/m2
Total Absorption Capacity 36% 36%
Maximum Setting Expansion 0.210% 0.210%
Density Wet 99.0 lb/ft3 1.58 g/cm3
Dry 69.0 lb/ft3 1.10 g/cm3
Set Time (Machine Mix)* 14-24 min. 14-24 min.
General Directions and Guidelines
Preparing the Mix Use potable water at temperatures between 70° and 100° F (21° and 38° C). Since variations in slurry (the plaster and water mixture) temperature produce variations in setting time, it is important to keep both the plaster and water in a stable temperature environment prior to use. The higher the temperature of the water, the shorter the set time. Weigh both the plaster and water for each mix. The water-to-plaster ratio is critical because it governs both the strength and the absorptive capacity of the mold.
Soaking Sift or strew the plaster into water slowly and evenly. Do not drop handfuls of plaster directly into the water. Allow soaking for 1-2 minutes. The plaster should be fully dispersed in the water prior to mixing. Small batches require less soaking than large batches. See bulletin IG503 for specific soaking instructions.
Mixing Mixing the plaster slurry is one of the most important steps in producing plaster molds with maximum strength, absorption, hardness, and other important properties.
Mechanically mixed plasters develop uniform molds with optimal strengths. Plasters can be mechanically mixed through
both batch and continuous processes. Proper blade and bucket dimensions are important for obtaining the best batch mix
(see IG503 for details). Longer mixing times result in higher mold strength and shorter setting times.
Pouring To prevent air entrainment and provide a uniform, smooth surface, careful pouring of the plaster slurry is necessary. Agitation of the filled case mold is a further step used to prevent air at or near the mold surface. Whenever possible, the plaster slurry should be poured carefully in the deepest area so the slurry flows evenly across the surface of the case mold.
Pouring a large amount of slurry directly on the face of the case mold may result in slight densification of the plaster mold
at the point where it strikes the surface of the case. This produces a hard spot, giving uneven absorption.
Drying All pottery molds should be dried as quickly as is safely possible after manufacture so that maximum physical properties can develop. Dry to a constant weight.
The best drying rooms or ovens provide (1) uniform and rapid circulation (minimum of 15-30 fps) of air with no “dead spots” having little or no air movement, (2) equal temperatures throughout the entire area, and (3) provisions for exhausting a portion of the air while replacing it with fresh air. High humidity surrounding the drying room or oven inhibits the efficiency of the drying because the air pulled into the room is incapable of picking up much moisture from the molds. The maximum temperature at which plaster molds are safe from calcination is 120° F (49° C). With substantial free water in
the mold, higher drying temperatures can be used without difficulty. As drying progresses, the temperature must be reduced to prevent calcination. The safe drying zone is in the shaded area of graph (below, right). Before removing molds from the dryer, the temperature should approach that of the area around the dryer to prevent thermal shock.
Mixing Ratios for slipcasting molds. No. 1 Pottery Plaster
Water
Plaster
1/2 Pint
11oz
1 Pint
1 lb 6 oz
1 Quart
2 lb 12 oz
1.5 Quarts
4 lb 2 oz
2 Quarts
5 lb 8 oz
2.5 Quarts
6 lb 14 oz
3 Quarts
8 lb 4 oz
3.5 Quarts
9 lb 10 oz
1 Gallon
11 lb
1.5 Gallons
16 lb 8 oz
2 Gallons
22 lb
2.5 Gallons
27 lb 8 oz
3 Gallons
33 lbs
KARI RADASCH's PLASTER NOTES (via Ian Anderson)
SUPER FORMULA
1 quart of water needs 3lbs of plaster
1) Measure width, length, and height of space. Multiply these numbers together: This is your TOTAL VOLUME. 2) Divide TOTAL VOLUME by 80. This gives you how many quarts of water you need. 3) Multiply quarts of water by: 3lbs. plaster for normal stuff. 2.85lbs. plaster for slip casting. 2.75lbs. plaster for really absorbent softer plaster. This gives you how much plaster you need for your water.
To find how much plaster you need for a space AND you can measure your object:
- Measure width, length, and height of space. Multiply these numbers together:
This is your TOTAL VOLUME.
2) Measure width, length, and height of object you are casting. Multiply these numbers together:
This is your OBJECT VOLUME.
3) Subtract OBJECT VOLUME from TOTAL VOLUME:
This tells you the VOLUME OF PLASTER YOU NEED.
4) Divide VOLUME OF PLASTER YOU NEED by 80:
This gives you how many quarts of water you need.
5) Multiply quarts of water by:
3lbs. plaster for normal plaster
2.85lbs. plaster for slip casting
2.75lbs. plaster for really absorbent softer plaster
This gives you how much plaster you need for your water.
Pottery Plaster Mix For Wedging Tables:
For wedging boards or tables mix 70 parts of water to 100 parts plaster. This equals 4.17 gallons water per 50 pounds dry pottery plaster.
Product Data
– The best material available for sanitaryware and dinnerware casting.
– Formulated for long life and reduced breakage (stronger molds).
– Available with or without thermal shock additive.
#1 POTTERY PLASTER is highly uniform, noted for outstanding performance and long life. The standard of the industry - this is the best material available for sanitaryware and dinnerware casting. Used for making plaster bats, wedging boards, and working molds. This is a relatively soft plaster which may be used for carving.
Technical Properties English Metric
Use Consistency (parts of water by weight per 100 parts plaster ) 70 70
1 Hr. Compressive Strength 1,000 psi 6.8 MN/m2
Dry Compressive Strength 2,400 psi 16.3 MN/m2
Total Absorption Capacity 36% 36%
Maximum Setting Expansion 0.210% 0.210%
Density Wet 99.0 lb/ft3 1.58 g/cm3
Dry 69.0 lb/ft3 1.10 g/cm3
Set Time (Machine Mix)* 14-24 min. 14-24 min.
General Directions and Guidelines
Preparing the Mix Use potable water at temperatures between 70° and 100° F (21° and 38° C). Since variations in slurry (the plaster and water mixture) temperature produce variations in setting time, it is important to keep both the plaster and water in a stable temperature environment prior to use. The higher the temperature of the water, the shorter the set time. Weigh both the plaster and water for each mix. The water-to-plaster ratio is critical because it governs both the strength and the absorptive capacity of the mold.
Soaking Sift or strew the plaster into water slowly and evenly. Do not drop handfuls of plaster directly into the water. Allow soaking for 1-2 minutes. The plaster should be fully dispersed in the water prior to mixing. Small batches require less soaking than large batches. See bulletin IG503 for specific soaking instructions.
Mixing Mixing the plaster slurry is one of the most important steps in producing plaster molds with maximum strength, absorption, hardness, and other important properties.
Mechanically mixed plasters develop uniform molds with optimal strengths. Plasters can be mechanically mixed through
both batch and continuous processes. Proper blade and bucket dimensions are important for obtaining the best batch mix
(see IG503 for details). Longer mixing times result in higher mold strength and shorter setting times.
Pouring To prevent air entrainment and provide a uniform, smooth surface, careful pouring of the plaster slurry is necessary. Agitation of the filled case mold is a further step used to prevent air at or near the mold surface. Whenever possible, the plaster slurry should be poured carefully in the deepest area so the slurry flows evenly across the surface of the case mold.
Pouring a large amount of slurry directly on the face of the case mold may result in slight densification of the plaster mold
at the point where it strikes the surface of the case. This produces a hard spot, giving uneven absorption.
Drying All pottery molds should be dried as quickly as is safely possible after manufacture so that maximum physical properties can develop. Dry to a constant weight.
The best drying rooms or ovens provide (1) uniform and rapid circulation (minimum of 15-30 fps) of air with no “dead spots” having little or no air movement, (2) equal temperatures throughout the entire area, and (3) provisions for exhausting a portion of the air while replacing it with fresh air. High humidity surrounding the drying room or oven inhibits the efficiency of the drying because the air pulled into the room is incapable of picking up much moisture from the molds. The maximum temperature at which plaster molds are safe from calcination is 120° F (49° C). With substantial free water in
the mold, higher drying temperatures can be used without difficulty. As drying progresses, the temperature must be reduced to prevent calcination. The safe drying zone is in the shaded area of graph (below, right). Before removing molds from the dryer, the temperature should approach that of the area around the dryer to prevent thermal shock.
Mixing Ratios for slipcasting molds. No. 1 Pottery Plaster
Water
|
Plaster
|
1/2 Pint
|
11oz
|
1 Pint
|
1 lb 6 oz
|
1 Quart
|
2 lb 12 oz
|
1.5 Quarts
|
4 lb 2 oz
|
2 Quarts
|
5 lb 8 oz
|
2.5 Quarts
|
6 lb 14 oz
|
3 Quarts
|
8 lb 4 oz
|
3.5 Quarts
|
9 lb 10 oz
|
1 Gallon
|
11 lb
|
1.5 Gallons
|
16 lb 8 oz
|
2 Gallons
|
22 lb
|
2.5 Gallons
|
27 lb 8 oz
|
3 Gallons
|
33 lbs
|
KARI RADASCH's PLASTER NOTES (via Ian Anderson)
SUPER FORMULA
1 quart of water needs 3lbs of plaster
1) Measure width, length, and height of space. Multiply these numbers together: This is your TOTAL VOLUME. 2) Divide TOTAL VOLUME by 80. This gives you how many quarts of water you need. 3) Multiply quarts of water by: 3lbs. plaster for normal stuff. 2.85lbs. plaster for slip casting. 2.75lbs. plaster for really absorbent softer plaster. This gives you how much plaster you need for your water.
To find how much plaster you need for a space AND you can measure your object:
- Measure width, length, and height of space. Multiply these numbers together:
This is your TOTAL VOLUME.
2) Measure width, length, and height of object you are casting. Multiply these numbers together:
This is your OBJECT VOLUME.
3) Subtract OBJECT VOLUME from TOTAL VOLUME:
This tells you the VOLUME OF PLASTER YOU NEED.
4) Divide VOLUME OF PLASTER YOU NEED by 80:
This gives you how many quarts of water you need.
5) Multiply quarts of water by:
3lbs. plaster for normal plaster
2.85lbs. plaster for slip casting
2.75lbs. plaster for really absorbent softer plaster
This gives you how much plaster you need for your water.
I can give you a digital file if you want to print out and make your own USG Volume and Mix guide.
Start purge at 23 degrees F above starting temperature
5 lbs of air pressure every 30 seconds
5 lbs of air pressure every 30 seconds
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