USG Casting Fireplace Surrounds - Manual (Page 18)

Use an Accurate Scale Use Proper Mixing Equipment
High-Volume Mixing When your business grows and you need to increase production, you will need to evaluate the use of high-volume
and Automation equipment, especially for mixing. There are several good high-volume mixers available, including those manufac-
tured by Blastcrete Equipment Company (www.blastcrete.com). At this point you may also want to consider
automating parts of your manufacturing process, such as pumping the gypsum cement slurry to the casting area
from the mixer. Any high-volume mixing and automation steps will also require additional molds and raw materials
for increased production.
Casting After the gypsum cement is mixed, it will then be immediately used in the molds. The molds need to be clean and
positioned properly for efficient casting.To ensure good casting techniques, you’ll need a work area that is not too
cramped and has large, sturdy tables with level surfaces.
First, a “face coat” is applied to the entire mold surface. This is the coat that will be seen on the finished part,
so it is extremely important to completely cover every mold detail with the face coat, removing trapped air and
replacing it with the slurry. When this coat begins to set but is still tacky, then subsequent coats containing
5% – 6% glass fibers or glass mat are applied. Sometimes the coats following the face coat can be poured,
depending on the design of the mold. We recommend that you first use the hand-layup method to cast your
parts, to gain familiarity with the materials and your processing capabilities. If pouring, we recommend that a
sealed displacement plug be used for thick parts to hollow out the back side of the mold. This will allow for lighter
parts, provide a means of anchoring the finished surround to the structure of the building, and minimize the
effects of the thermal forces on the finished product. If the plug is to be removed, make sure it is tapered or beveled
to simplify removal.
Production
Process Flow
18 Casting Fireplace Surrounds