Santa Cruz County History - Making a Living



The Laguna Limekilns: Bonny Doon
by Robert W. Piwarzyk

[This article is excerpted from a manuscript titled, "The Laguna Limekilns: Bonny Doon," pp. 44-45. The maps, drawings, and photos of the manuscript are not included on this site. The manuscript is copyrighted 1996 by the author. It is used here with permission.]

Kiln Descriptions

The Laguna limekilns are two, open top, side-by-side, top loading pot kilns that were built into the hillside such that the back and side walls are supported by the earth. All walls are made of locally quarried and faced limestone, and are rubble filled with mortar. The front walls have two archways in each kiln. Each archway provides access to a fire chamber (also called the "tunnel" or "arch"), which is an arched tunnel constructed from the limestone ore as it is loaded into the kiln. This tunnel extends from the front wall to the back wall and straddles the fire chamber floor.

The front walls are supported by three integral buttresses, one on each side of the kiln face and one in the center. There is no evidence that the work area between these buttresses had a roof, as is seen at other sites (UCSC and Fall Creek). The archways are constructed with flat lintel stones spanning the width of the opening. There is no evidence that the fire chamber had doors. Impressions in extant mortar indicate that this passage was lined with firebrick which was arched, and that the interior walls of the kilns were lined with firebrick. The floors of the kilns had fire chamber floors, which extended from the front wall to the back wall, and were also made of firebrick. Most of this brick was imported from Europe and is discussed under "Firebricks at the Laguna Limekilns." Scale drawings of the kilns are presented in appendix B. [Not included on this site.]

Generally, the Laguna limekilns are in excellent condition. A few small trees are growing on, in, and in front of the kilns. Damage seems to be minimal from the roots. The front wall of the right kiln bows out approximately 8" at the top, is missing the top 12" of rocks, and has an offset of 2" with the center buttress. The lintel stone of the right-hand arch has cracked both horizontally and vertically. The outer lower piece has fallen. It is hard to determine if this failure has caused the wall to bow or if the wall failure caused the lintel to fail. Small cracks in the buttress walls are most likely due to settling, or seismic forces, however the kilns have not changed any in the 20 years observed by the author.

The top row of rocks around the inside perimeter of the kiln was usually made with flat rocks, and was called a "curb," or "cap." All the capstones are missing from both kilns. It seems likely that they were salvaged for another use as only a few are found in the rubble inside the kilns.

The floors of the limekilns are covered with rubble up to 1' deep, which contains chunks of firebrick, cans and broken bottles, and other small pieces of trash. When surveying the kilns, an area was cleared in order to determine a datum elevation. It was discovered that the floor of the fire chamber was constructed of firebrick! This feature would help reflect the heat from the fire back into the kiln, and would make it easier to remove ashes from the fire chamber. This is the first indication that this was ever done. No other site has any evidence that a floor exists. If there are any others, they are covered with rubble.

The brick are laid on edge, in what is either refractory mortar or fireclay, with seven rows extending lengthwise from front to back, and an edge row laid perpendicular to these on each side, for a total width of three feet. About three feet of brick have been removed from in front of each arch on the left kiln. The firebrick floor extends to the back wall but the last three bricks are stepped up (see photograph [not included on this site]). The right kiln was only probed enough to confirm that it also has a floor on the left fire chamber. No floor was found at the right arch.

At the base of the left wall of the left kiln, an impression of a firebrick laying flat and perpendicular to the wall was uncovered. The end of this brick was 16" out from the limestone wall, which would locate the surface of the firebrick lining. The space in between had been filled with chunks of brick pieces embedded in a red clay. It is deduced that after the lining was removed, the inner layer of brick pieces pealed off, leaving some red clay adhered to the limestone walls. The bricks lining the back wall were set against the limestone wall with only the red clay used as a filler. The bricks lining the front wall were set in cement mortar, which is extant with chunks of brick as a filler and impressions of brick ends. Therefore, dimensions as measured to the limestone walls must be reduced by approximately 18" (the length of two 9" brick) front to back, and approximately 32" (the length of two 9" brick plus filler) side to side, to deduce the interior dimensions of the lined kiln.

The rubble on the floors of these kilns is higher in the center. There are ridges, extending front to back, on both sides of each fire chamber floor. Possibly this is due to the manner in which the fire chamber arches were built as the kiln was loaded. With use, the quicklime crumbles and accumulates on the floor, where it naturally hydrates and hardens. Redwood roots, probably from the stand in front of the kilns, lie on top of this hard-packed floor. Their removal would not affect the trees.

The left kiln face and buttress walls have been pointed up with Portland cement mortar. Larger spaces were chinked with firebrick in several places. The right kiln has very little pointing remaining, if it was ever there. Overall, the left kiln is in better condition. It is possible that use of the right kiln was discontinued, due to the failed wall and lintel, before the left kiln was abandoned.

The right kiln has several items worth noting. The lintel stone in the right arch was cracked through a hole drilled into the stone. This is the only tool mark to be seen on the site, as drilling is not in evidence at these quarries. Holes are found in the large rocks in the UCSC kilns. They provided a means of lifting and moving them from the quarry and into position with block and tackle rigging. This 1" diameter hole is about 4" deep and has a snub nose with an irregular surface such as would be made by a star drill.

There is a solid metal rod at the left hand base of the left arch, whose purpose is not known. It is 1" diameter and 14" long, and could be a drill bit (although the end seems to be broken and not hammered) or a rigging bar that got stuck in a hole and could not be removed. The rod protrudes from the wall between two blocks and whether it is embedded in a hole, or not, can't be determined. Possibly the rod was part of a bracket or pivot for mounting a kiln door, but there are none on the other arches.

The following two pages summarize each of the Laguna limekilns.

Laguna Limekilns - "Left Kiln"

Looking East

Date: H.T. Holmes Lime Company's "new kilns." Construction noted December, 1899. Date closed unknown, maybe ca. 1912.

Description: Hillside, top loading pot kiln. Walls are mixed shaped and unshaped limestone. Interior randomly laid with mortar. Front wall of nine lifts, and buttresses of seven lifts are dressed, laid with lime mortar, and are pointed-up with Portland concrete cement. These walls are rubble-filled with mortar. Some coving at top. Interior corners have small, varied radii. Has fire chamber floors.

Number of arches: Two

Dimensions: (Heights measured from original kiln floor.)

Interior: 18' 10" wide x 15' 10" high x 13' 9" deep
(firebrick lining thickness not included; see text.)
Front wall thickness: 5'
Arches: 3' 3" wide (avg.) x 6' 0" high

Firebricks: Inside front wall has mortar with brick filler. Impressions indicate that kiln walls were lined with brick laid horizontal, face up, ends to wall. Thirteen named brick show that most were imported from Scotland, England, and Belgium. Regular, arch, and wedge brick were found. Fire chamber floors are made of firebrick laid on edge.

This kiln is in excellent condition, except for the soft, crumbling red mortar in the interior walls. All of the wall capstones are missing and the kiln floor has about 1' of rubble. Small (4-6" diameter) trees are growing in and on the kiln. The left hand buttress has a minor crack running through the wall.

Mitigation: Remove small trees from kiln.

Laguna Limekilns - "Right Kiln"

Looking East

Date: H.T. Holmes Lime Company's "new kilns-" construction noted December, 1899. Date closed unknown, maybe ca. 1912.

Description: Hillside, top loading pot kiln. Walls are mixed shaped and unshaped limestone. Interior randomly laid with mortar. Front wall of nine lifts, and buttresses of seven lifts are dressed, laid with lime mortar, and are rubble filled with mortar. These walls lack pointing-up mortar. Some coving at top. Interior corners have small, varied radii.

Number of arches: Two

Dimensions: (Heights measured from original kiln floor.)

Interior: 19' 3" wide x 16' 10" high x 14' 6" deep
(firebrick lining thickness not included; see text.)
Front wall thickness: 5' 2"
Arches: Left arch - 3' 3"wide x 5' 9" high
Right arch - 3' 6" wide x 5' 6" high

Firebricks: Inside side walls have mortar with brick filler at the base. Thirteen named brick show that most were imported from Scotland, England, and Belgium. Regular, arch, and wedge brick were found. May be fire chamber floors.

Condition: Front wall bowed out 8 inches at top. The right arch lintel stone is cracked and a piece is missing. All of the wall capstones are missing and the kiln floor has about 1' of rubble. Three stones missing from center buttress face. Small (6-8" diameter) trees are growing in, on, and in front of the kiln.

Mitigation: Remove small trees from kiln. Replace stones and point-up front walls. Brace lintel and front walls.

>>Continue with: Firebricks at the Laguna Limekilns

Bibliography

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Bonny Doon, kilns, limestone

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