Date: October 6, 2008 

 (Finalized: December, 8, 2008) 

Subject: Site Visit – Kohler Company, Spartanburg, South Carolina 

Clay Ceramics Manufacturing NESHAP 

EPA Contract No. EP-D-06-118; EPA Work Assignment No. 2-09 

RTI Project No. 0210426.002.009 

From: Gabrielle Raymond 

 Tom Holloway 

To: Jeff Telander 

EPA/SPPD/MMG (D243-02) 

U. S. Environmental Protection Agency 

Research Triangle Park, N.C. 27711 

I. Purpose 

The purpose of this visit was to observe the clay ceramics manufacturing process at the 

Kohler Company (Kohler) facility in Spartanburg, South Carolina, and to collect information on 

sources of hazardous air pollutant (HAP) emissions and emission controls in support of the 

redevelopment of national emission standards for hazardous air pollutants (NESHAP) for the 

clay ceramics manufacturing industry. 

II. Place and Date 

Kohler Company. 

Post Office Box 1987 

Spartanburg, South Carolina 29304 

August 5, 2008 

III. Attendees 

Kohler Company 

 

Mike Cassidy, Environment, Health, and Safety Specialist 

Telephone: (920) 457-4441, ext. 77263 

U. S. Environmental Protection Agency 

Jeff Telander 

Telephone: (919) 541-5427 
 

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RTI International 

Tom Holloway 

Telephone: (919) 316-3733 

Gabrielle Raymond 

Telephone: (919) 541-7015 

IV. Discussion 

A. Background 

The Kohler facility in Spartanburg, South Carolina, manufactures ceramic sanitaryware. 

Kohler also operates sanitaryware manufacturing plants in Kohler, Wisconsin, and Brownwood, 

Texas. The Spartanburg facility, which was constructed in 1958, consists of two plants: the 

Plastics Plant and the Ceramics Plant. The Plastics Plant produces fiberglass bathtubs and 

shower stalls. The Ceramics Plant produces several vitreous sanitaryware products, including 

sinks, toilet bowls, toilet tanks, and other sanitaryware products. The Spartanburg facility has 

been determined to be a major source of HAP emissions due to styrene emissions from the 

Plastics Plant. Because the scope of this project is limited to clay ceramics, only limited 

information on the Plastics Plant was obtained during the visit, and the Plastics Plant is not 

discussed further in this report. The Spartanburg facility operates 24 hours per day, 7 days per 

week. 

The Spartanburg and Brownwood facilities manufacture high-volume sanitaryware 

products, while the Wisconsin facility produces low-volume specialty sanitaryware products. 

The Spartanburg plant has a total of six tunnel kilns and three shuttle kilns, all of which are gasfired. Four of the tunnel kilns (Kilns 1 through 4) were constructed in 1959, one tunnel kiln 

(Kiln 8) was built in 1994, and the last tunnel kiln (Kiln 10) was built in 2005. Two of the tunnel 

kilns (Kilns 3 and 4) are currently off-line due to market conditions. Of the four operating tunnel 

kilns, three are used for first fire (Kilns 2, 8, and 10), and the other (Kiln 1) is used for refire. 

Refire kilns are used to fire products that had previously been fired but had minor defects, which 

were subsequently repaired. All three shuttle kilns (Kilns 6, 7, and 9) are in operation and are 

also being used for refire. 

B. Process 

The basic process steps used at the South Carolina facility include raw material storage, 

glaze preparation, slip preparation, ware forming, drying/finishing, glazing, firing, and 

inspection. The following paragraphs describe the manufacturing process in more detail. 

1. Raw Material Storage 

The primary raw materials used at the plant include ball clay, kaolin, sand, feldspar, and 

flint. In addition, the facility uses several other materials, including stains, binders, antifoaming 
 

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agents, fungicides, algaecides, and plaster-of-paris. Clay comprises at least 90 percent of raw 

materials used in ceramic sanitaryware manufactured by Kohler at the Spartanburg plant. All 

materials are received by truck. Kaolin and ball clay are received in tanker trucks as slurries 

because slurries allow for better uniformity and blending of raw materials and eliminate the need 

for milling the materials onsite. The other materials are received dry. 

2. Glaze Preparation 

Glaze making is a batch operation, which is specific to the color of the glazed product. 

Glaze materials are received as dry materials and are metered out into a weigh hopper. After the 

dry materials are batched in the weigh hopper, the materials are placed in a ball mill, where 

water is added to make the glaze, which is 70 percent solids. The mixed glaze is then discharged 

into totes, which are transferred by forklift to the glaze spraying area of the plant and hooked up 

to specific glaze spray booths.

3. Slip Preparation 

In the slip-making process, clay slurry is pumped from storage tanks to a blunger, where 

dry materials and additives such as deflocculants and fungicides, are added and mixed. From the 

blunger, the slip is pumped into an underground mixer for aging (24 to 96 hours). Waste slip is 

screened and recycled back to the process. 

4. Ware Forming 

The plaster production molds are manufactured on-site in the mold shop. To make the 

plaster production molds, dry plaster and water are processed in a mixer to form a plaster slurry. 

The slurry is then poured into a case mold. The plaster sets up in 15 to 30 minutes. Next, the 

plaster production mold is removed from the case mold and dried in one of two natural gas-fired 

dryers. After drying, the plaster mold is ready for the sanitaryware casting step. 

Kohler uses two types of casting processes: pressure casting and manual slip casting. 

Pressure casting can be used for simple shapes, such as pedestals and toilet tanks. For more 

complex shapes, such as toilet bowls, manual slip casting is used. For either type of casting, the 

aged slip is pumped from the mixer to the casting shop. For manual slip casting, the slip is 

deposited into a plaster of paris mold. Capillary action draws the liquid out of the slip while 

building up a layer of solids over the inside surface of the mold, forming the body of the ware. 

After approximately 1 hour, excess slip is emptied out to allow the cast form to set up. Then, the 

mold is disassembled, and the ware is removed for air drying. At this point, the ware contains 

approximately 30 percent moisture. Pressure casting is a similar process except that, instead of 

relying on capillary action, hydrostatic pressure is applied to drive the liquid out of the slip. 

After casting by either process, the waste slip basins are transported to open storage bins 

in the raw materials mixing area, where the waste slip is screened to remove large pieces and 

contaminants before it is recycled back into the process. 
 

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5. Drying/Finishing 

After casting, the unfired ware, called “greenware,” is placed on racks for drying. Some 

ware is air-dried at room temperature for 3 to 4 days; some ware is air-dried and placed in a 

tunnel dryer for further drying; and some ware is placed directly into tunnel dryers. Before the 

ware is dried, it is green-finished to remove seams and burrs. Finishing is performed manually 

using a wet sponge and a palatte (scraper). The racks of greenware are then transported by 

forklift to one of several dryers, two of which are gas-fired and the others steam-heated. The 

steam-heated dryers are heated by a boiler that is supplemented with waste heat from some of the 

kilns. Dryer operating temperatures are approximately 60oC (140oF). 

6. Glazing 

After drying, the greenware is transported to the glaze shop. The same basic process 

steps and raw materials are used for producing clay slip and glazes to ensure that the glazes 

expand and contract at the same rate as the body of the ware; otherwise, cracking and other 

defects would occur. The primary difference between the raw material mix used for the ware 

body and for glaze is that antifoaming agents, binders, and stains are added to glazes. Stains 

contain small quantities of zinc, cobalt, chromium, and nickel. 

The glaze materials are loaded into a weigh hopper and proportioned. The hopper feeds 

the materials and water into a ball mill, which serves primarily as a mixer. From the ball mill, 

the glaze is applied either manually or mechanically in one of the three types of spray booths 

operating at the Spartanburg facility--robot, automated, and manual. The booths are equipped 

with water curtains and baffles to remove large particulate matter (PM) from the over spray. The 

water curtains drain into basins below the booths and then to a clarifier for pre-treatment (solids 

removal). The baffles are manually scraped to reclaim some of the glaze material. Note that 

there are no defined process lines, and a piece of ware can be glazed in any booth and fired in 

any kiln. 

The plant also has spot spray booths and one respray booth used for touching up or 

reglazing ware. The spot spray booths are exhausted to fabric filters, and the respray booth has a 

water curtain for controlling emissions. 

After glazing, the ware is manually placed on racks for short-term storage prior to 

loading onto kiln cars for firing. There are no product lines; ware can go from any spray booth 

to any kiln. All defective pieces that have not been fired are recycled. The recycled pieces are 

sent from a storage area on the floor, where they are emptied into a blunger by forklift. 

7. Firing 

As noted above, Kohler uses tunnel kilns to fire green sanitaryware. For the tunnel kilns, 

which operate continuously, the ware is loaded onto kiln cars that are pushed into the kiln one 

car at a time according to a set schedule. As the kiln cars are pushed through the kiln, they pass 

through various zones characterized by increasing temperature, up to the peak temperature of 
 

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about 2200° to 2300°F in the firing zone. From that point, the temperature decreases as the kiln 

cars continue to be pushed through, and the ware is gradually cooled. 

Shuttle kilns are batch process units, which are used to fire a single kiln load of ware. 

The kiln car is pushed into the kiln, which is then closed. The burners are ignited, and the 

temperatures are gradually ramped up to a peak firing temperature, then ramped down to 

complete the cycle. The typical kiln cycle for the shuttle kilns at Kohler is 24 to 42 hours from 

the time when the kiln is loaded and the burners are ignited, to the time when the fired ware has 

cooled enough to be removed (cold to cold). 

8. Inspection 

After firing, the product is unloaded from the kilns cars, inspected, finished with a 

grinder, water-tested, and packaged for shipment. If the fired ware has minor defects, the ware is 

machined, reglazed, and refired in one of three shuttle kilns or in the refire tunnel kiln at a 

temperature of approximately 2100°F. If the defect cannot be repaired, the ware is discarded. 

C. Emissions and Controls 

The South Carolina facility uses a combination of wet scrubbers, fabric filters, and water 

curtains to control emissions from the process. Emissions from dry glaze batching and milling 

are controlled with a baghouse that exhausts outside. As noted above, emissions from glaze 

spraying booths are controlled with water curtains. Emissions from the ware grinder are 

controlled with a fabric filter. Emissions from the dryers and kilns are uncontrolled, except for a 

caustic scrubber installed on Kiln 10 to comply with the original Clay Ceramics NESHAP. 

However, Kohler is in negotiations with the State of South Carolina to have the scrubber shut 

down in light of the vacature of the original Clay Ceramics NESHAP. The South Carolina 

Department of Health and Environmental Control (SCDHEC) published a proposal to repeal the 

state-only Clay MACT rule in the September 25, 2008 State Register. Kohler Co. expects the 

state-only rule to be repealed in early 2009, after which time the wet scrubber on tunnel kiln 10 

will be shut down.