United States Gypsum Industrial Plaster & Gypsum Cement Products

FAST CAST Exterior Gypsum Cement

FAST CAST Exterior Gypsum Cement is a fast-setting cementitious product suitable for use as a casting material to produce decorative exterior figurines. When mixed with sand, FAST CAST cement produces strong, hard casts that can be demolded in one hour, resulting in increased productivity over conventional cements.

Recommended Mix Design

50 lbs. FAST CAST Exterior Gypsum Cement
50 lbs. sand (fine aggregate)
1 1/2 gallons (U.S.) water
(Water measurement may have to be adjusted for particle size and water content of sand.)

Sand should be clean, dry, and properly sized. It should be free from dolomitic contamination and conform to ASTM C33. An example of a suitable commercially available sand is All Purpose Sand.

Mechanical Mortar Mix Procedures

1. With the mixer operating, add half of the sand to the water.

2. Carefully strew or sift the FAST CAST cement into the mixer.

3. With the mixer operating, carefully add the remainder of the sand.

4. Mix thoroughly until lump free - 2 to 3 minutes, but no more than 5 minutes.

5. Carefully pour the slurry into the mold to prevent entrapped air. Agitate the filled mold to assist in removing any noticeable air bubbles or entrained air.

6. Set time is 25-35 minutes. Allow casts to remain in the mold for approximately one hour after set to ensure the adequate "green strength" necessary for demolding.

7. Demold and transfer the cast to a suitable drying area. Bench dry the castings to a constant weight before packaging for shipment. If the drying time must be accelerated, castings can be placed in a drying room capable of producing both increased air circulation and drying temperatures.

Maximum temperature in a drying room should not exceed 120°F.

Mechanical Mixing - Variable Speed Propeller Type Mixer

1. Add the sand to the water.

2. Carefully strew or sift the FAST CAST Gypsum Cement into the mixing container.

3. Use a high-speed, variable-drive propeller mixer to disperse the slurry. Mix for 2 to 3 minutes, but no more than 5 minutes.

4. Carefully pour the slurry into the mold to prevent entrapped air. Agitate the filled mold to assist in removing any noticeable air bubbles or entrained air.

5. Set time is 25-35 minutes. Allow casts to remain in the mold for approximately one hour after set to ensure the adequate "green strength" necessary for demolding.

6. Follow drying procedures highlighted in step 7 of the previous section.

FAST CAST Exterior Gypsum Cement
Typical Physical Properties

Use Consistency .......................12.5 cc/100 g of slurry
Set Time - Vicat.........................25-35 minutes
Wet Density...............................131.0 lb./ft³
Dry Density................................110.0 lb./ft³
Dry Compressive Strength..........8000 psi
% Setting Expansion (maximum) 0.1
1-Hr. Compressive Strength........2500 psi

Precautions

1. Water purity is important. Water should be as pure as possible. Typically, if water is drinkable, it is probably suitable for mixing the product. Water contaminated with organic impurities, soluble salts, and other chemicals may cause detrimental effects to FAST CAST cement.

2. Proper mixing ensures dispersion of the FAST CAST cement powder into the water. Accurately weighed water and powder is necessary to assist in fabrication of quality castings.

3. Timing mix cycles is essential. For best results, mechanical mixing methods should be used.

4. FAST CAST Exterior Gypsum Cement is not a suitable product for the fabrication of bird baths, water fountains, or other applications where constant exposure to water occurs; nor is it suitable for casting planters or flower potting containers.

5. FAST CAST Exterior Gypsum Cement is not suitable for structural or non-structural exterior architectural applications.

Consistency Test

When mixing FAST CAST Exterior Gypsum Cement, it is important to get the correct consistency by using the correct amounts of FAST CAST Cement, aggregate, and water. Follow the steps described below to test the consistency of a FAST CAST cement mixture.

Supplies:

2" diameter x 4" high (inside dimensions) brass open-ended cylinder
1-qt. flexible mixing bowl
Wide, stiff metal spatula ( 1-1 ¼" wide x 4-5" long)
Flat smooth surface (PLEXIGLAS® Sheet)
Ruler with 1/8" markings
Balance (0.1 g accuracy)
Graduated cylinder

Test Method:

1. Weigh correct proportion of FAST CAST Exterior Gypsum Cement and aggregate to obtain a total mix of at least 500 grams. (The ratio of aggregate to FAST CAST cement is 1:1.) Thouroughly dry blend the additives together. The aggregate should be dry and at room temperature prior to testing.

2. Using a balance or graduated cylinder, accurately measure out 62.5 cc of water into a mixing bowl.

3. Measure out 500 grams of aggregated FAST CAST cement. Slowly sift the mixture into the water and allow it to soak undisturbed for one minute.

4. Vigorously stir the mixture for one minute by hand with a wide stiff metal spatula, stiring 180-200 revolutions. Scrape the sides of the bowl to insure that all materials are thouroughly mixed.

5. Place the 2" x 4" cylinder on the PLEXIGLAS sheet. Immediately fill the cylinder with the slurry, puddling to eliminate air voids. Strike off any excess slurry from the cylinder top.

6. Slowly raise the cylinder 1.5" above the PLEXIGLAS sheet, allowing the slurry to flow onto the sheet.

7. Once the flow has ceased, measure the diameter of the patty in at least two directions. The correct diameter of the patty should be 7" (+- 1/8"). If the patty diameter is not this size, repeat procedure from step 1 and increase or decrease the amount of water used accordingly.