Christopher Andreae,  Historica Research Limited, March, 2007

Introduction

The ruins of a lime-burning Hoffman kiln lie halfway up the slope of the Niagara Escarpment at the Forks of the Credit.  A couple of hundred lime kilns were built in Ontario and a few dozen of these were large, industrial operations.  The Forks of the Credit kiln is unique as probably the only Hoffman kiln used for lime burning in North America.

From about the 1870s until well into the 20th century, large-scale, lime-burning operations in Ontario used vertical shaft kilns.  [Figure 1]  These provided for the continuous production of lime.  Two types were used, furnace fired and mixed feed.  In a furnace fired operation, the fuel and limestone were kept separate.  In a mixed feed, the stone and fuel were mixed together.

The main attraction of the Hoffman kiln over other designs was its fuel efficiency.  Under optimal conditions, a kiln could produce eight tons of lime per ton of coal used.  The vertical, furnace-fired kiln widely used in the lime industry could produce only two-three tons of lime for each ton of coal.

One of the main economic objections to the Hoffman Kiln was that the cost of labour to empty the lime was almost as great as that of charging the kiln. [Figure 3]  In a vertical shaft kiln, the burned lime fell by gravity through the kiln and was removed with negligible labour costs.  A Hoffman kiln with an output of 24 tons per day normally required about 13-14 men as compared to five men for a shaft kiln of the same output.

Another problem was that the capital cost of a Hoffman kiln was about twice the cost of a vertical shaft kiln.  If fuel costs were high and labour cheap, a Hoffman kiln could be economic.

The Hoffman kiln – as with any continuous kiln – was most efficient when operated continuously.  The design had less flexibility in adjusting for production variations than the vertical kiln and lost much of its fuel economy when worked below capacity.  This was a serious disadvantage in markets were variables demands for.

Plan of 14 chamber Hoffman Kiln.  Dashed arrow direction of filling burning and unloading process; solid arrow, direction of air movement in kiln.  Chamber 1 being filled; chambers 2-5 preheating with hot gases from burning; chambers 6-7 burning; chambers 8-12 cooling and preheating air for burning chambers; chamber 13 being emptied; chamber 14 empty Source: Adapted from Searle, Limestone, 369.

The size of Hoffman kilns was usually given as the number of chambers in the kiln.  The usual number was somewhere between 16 and 20 chambers.  [Figure 4]  More chambers allowed for greater variation in capacity. In a brick kiln walls actually divided the kiln ring into chambers.  The wall was dispensed with in a lime burning operation.  Although the kiln was still described by number of (physical) chambers, in effect, the kiln was divided into (imaginary) zones.  Chambers were roughly 12 feet long. The operation of these kilns is well described in technical literature.

Hoffman Kiln, Forks of the Credit

The ruins of the Hoffman Kiln are located on the E½ of either Lot 8 or 9, Concession IV, W of Hurontario. [Figure 5]  The Forks of the Credit were best known in the 1880s-1900 for the quality of the sandstone.

By 1891 most of the sandstone production at the Forks was in the hands of Robert Carroll and John B. Vick.  In 1896 they consolidated their operations into the Credit Forks Mining and Manufacturing Company.  They also built the Hoffman kiln.  This was the first documented use of burning lime at the Forks of the Credit.

The difficulty faced with sandstone quarrying at the Forks was that the beds were overlain by a thick layer of dolomite.  As the exposed sandstone was removed, quarry operators had to tunnel under the limestone to continue operation.  Simply blasting away the limestone was considered uneconomic.  Instead, using the stone to make lime (and decades later, crushed stone) would produce a commercial product as well as open new sandstone supplies.

The lime operation was spectacularly unsuccessful.  It was closed within three years.  Whether this was due to problems with the kiln operation or the economic viability of the sandstone quarries is moot.  According to one interpretation, the kiln was closed because wind conditions near the escarpment caused a down-draught in the chimney.  The very tall chimney visible in Figure 5 was typical of a Hoffman kiln. [Figure 2]  The difficulty of relying on natural draught for any kiln – not just the Hoffman design – was also well known at the time.

Yet not just the kiln closed; sandstone quarrying was suspended.  This suggests economic problems with the entire quarry business.  Most likely, the sandstone operations were uneconomic.  Perhaps the kiln had been so expensive to construct that it affected the financial viability of the entire company.

Brick-Burning Hoffman Kilns in Ontario

Why a Hoffman kiln design was used at the Forks-of-the-Credit remains unanswered.  The vertical, stack – such as used at nearby Limehouse – was the preferred industrial kiln design in Ontario 

There are at least two possible explanations.  One may lie in the backgrounds of Carroll and Vick, and their company, the Credit Forks Mining and Manufacturing Company.  Did they, or their associates, have some knowledge or experience with Hoffman kilns especially at Ontario brickyards?  More research into their backgrounds might find an answer.

There was a late 19th century mini-boom in Hoffman kiln installation in Ontario brickyards.  Indeed the kiln had been originally designed for firing bricks.  The economics of firing bricks was different than that of lime burning such that the Hoffman design was quite suitable in Ontario. 

Most particularly, unloading a brick kiln was always a labour intensive activity.  There was no option for gravity discharge as was possible with a vertical lime kiln.  Therefore labour costs in unloading were not a consideration in selecting a brick kiln design; they were in a lime kiln. 

The market for brick was greater, and relatively speaking, more constant than for lime.  Lime could, and was, imported by rail from large producing states such as New York.  Brick, by contrast was a heavier, lower value product that was more sensitive to long-distance shipping costs.  Therefore, there was greater opportunity to run a continuous brick-kiln; unlike the domestic lime industry.

The exact number of Hoffman brick-kilns operated in Ontario is not known.  Two are known for certain, three were built as Youngren kilns (a variant of the Hoffman), and three are not specified.  Others were built elsewhere in Canada.  A Hoffman brick-burning kiln was used in Quebec City until 1964.  The actual difference between Hoffman and Youngren kilns was not established.  One difference was that the Youngren was fired with coal gas (producer gas) while the Hoffman used solid coal.

The Joseph Russell Brick Yard, on Queen Street East, Toronto was using a 16-chamber Hoffman Kiln by 1905.  [Figure 7]  A complete burning cycle for the ring took 16 days.  By 1930 the kiln seems to have been rebuilt into three batch kilns.

The Port Credit Brick Company was using a slightly larger 18 chamber Hoffman kiln by 1905.  [Figures 8]  The burn cycle also took 16 days and the 1906 Bureau of Mines Report provides a description of the burning operation.  The Port Credit plant was closed in 1923 and acquired by the Cooksville Brick Company.  The Hoffman kilns were abandoned and replaced with more traditional down-draught kilns.

Joseph Russell Brick Yard, Toronto. Source : Ontario Bureau of Mines, Clay Industry , 1906.

The Cooksville Brick Company operated three, 16-chamber Youngren kilns at its Cooksville plant.  The burn cycle was 30 days.  The date of opening was not established but by 1930.  These kilns were used until 1968.

In addition to the identified kiln types, the Don Valley Brick works in Toronto had two continuous kilns in operation in 1905.  By 1930 the company had a single, 20-chamber continuous kiln.  The Toronto Brick Company installed a continuous chamber kiln, possibly in 1912.  By 1930 the company had modified its chamber kiln into three ordinary, rectangular batch kilns.

Conclusions

To date only two photographs and very little documentary evidence of the Forks-of-the-Credit kiln. 

Material evidence defines the scale of the site.

It seems like the Ontario Hoffman brick kilns were similar in size to that at the Forks.
Hoffman lime-burning kilns common in Britain; not in North America.  As a brick kiln, the design was more popular – in Ontario it was used for about 30 years.

Unique industrial site.  Scale, technology employed; associated with sandstone industry at the Forks.

Issue of technological transfer – from where?  Why used?. 

Kiln is a fragile resource – ought to be stabilized.