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Canadian Historic Sites: Occasional Papers in Archaeology and History No. 12

Lime Preparation at 18th-Century Louisbourg

by Charles S. Lindsay

The Second Kiln

The Kiln

Following the vitrification of the first kiln a smaller but more elaborate second kiln was built within its walls. This new kiln was radically different from its predecessor both in form and operation. It was basically an inverted cone with three openings at the base of the wall giving access to the interior of the kiln. At the base the internal diameter was 7.2 ft., and when excavated its walls survived to a height of about 9 ft. above the base.

Excavation between the walls of the two kilns revealed that the wall of the second was constructed in several discrete vertical stages. Each stage was built with a sloping inner face and a vertical outer face to create the inverted cone shape of the kiln. The area behind, between the back of the wall and the inner face of the first kiln wall, was then filled with earth up to the top of each stage. Since the bottom of each new stage was wider than the top of the one beneath, succeeding stages were partly supported on the earth fill behind the wall. The resulting profile consisted of a series of steps at the back and a smooth slope at the front. The advantage of this type of wall lies in keying the masonry into the material supporting it, thereby providing greater stability. Examples are to be seen in Figure 1, 2, 3, where it was used in the construction of lime-kilns of this period in France.

The original height of the second kiln is not known. It would seem that it could not have been any higher than the point at which the outward progression of the cone shape intersected the inner face of the kiln wall; however, the sloping sides of the cone were rather irregular, so this point cannot be accurately calculated. All that can be said with certainty is that it was originally higher than it survived, though probably not as high as the first kiln.


Three drawholes were established, equidistantly spaced around the base of the wall and opening into the kiln on the north, west and southeast sides. Access to the drawholes was gained through alcoves (Figs. 14, 15, 16) cut through the lower part of the first kiln wall.

In order to create the alcoves it was first necessary to excavate passageways through the hillside on the north and west down to the base of the first kiln wall. The wall was then breached and retaining walls were erected to hold back the fill of earth between the walls of the two kilns. Next the breach and the area between the walls was arched over. The resulting alcoves were shortened versions of the galerie voûtée described by Diderot (Fig. 5, a) 5.8 ft. long and 3.6 ft. wide, which provided a sheltered place from which the lime could be drawn.

The North and West Drawholes

Both the north and west drawholes (Figs. 14, 15) were substantially similar and therefore will be considered together. In both, the actual opening was 3.25 ft. wide on the outside, narrowing to a width of 2.3 ft. at the inner edge. Both openings were 2.5 ft. high and both set in a wall about 2 ft. thick. The jambs of the north drawhole were brick starting at the base of the wall with an offset on the outside for the first six courses. However, since the side walls of the alcove were built on top of this offset it does not appear to have served any purpose. The jambs of the west drawhole (Fig. 15) were of rubble masonry except for the outer corner of the right-hand jamb, which was of brick. In this case the lowest courses of the kiln wall ran beneath the base of the jambs.

Both drawholes had similar arches consisting of oblong blocks of fieldstone set on their sides radially around the intrados. Each arch was supported by three iron bands 2 in. wide, 0.5 in. thick, curved to follow the arch and anchored into the jambs with short horizontal terminals (Fig. 17).

14 The north drawhole from inside the second kiln.

The side walls of the alcoves were only one stone thick and primarily served as facings rather than as functional, load-bearing walls. Behind these facings, in the gap between the two kiln walls, there were piles of unmortared rubble-stone which absorbed most of the lateral thrust of the earth packing and supported the ends of the arches over the alcoves. The lower portions of the side walls of the alcoves must have been built after the drawholes were completed, since in the north alcove the walls overlay the offset at the base of the jamb and abutted the back of the second kiln wall. However, the upper part of the side walls above the top of the drawhole opening bonded into the back of the kiln wall. The implication is that the drawhole was built first, then the side walls of the alcove up to the top of the drawhole, then the upper part of the first stage of the kiln wall and the upper part of the alcove walls together.

15 The west passageway, alcove and drawhole of the second kiln. The vertical sides of the excavation are the sides of she original passageway.

The arches over both alcoves abutted the back of the second kiln wall, 1.6 ft. above the top of the opening on the north drawhole and 2.5 ft. above on the west drawhole. Both arches were built across the top of the side walls rather than springing from them, and rested partly on the piles of rubble behind. They were built with shallow arcs, the crown being only 4 in. to 6 in. above the springer, and were supported during construction by wooden scaffolding, the marks of which could still be seen in the mortar on the underside of the arch. Since these arches abutted the back of the kiln wall and since the second vertical stage of the kiln wall rested on top of the arch in the west drawhole, they must have been constructed after the completion of the first stage of the wall and before the start of the second stage.

The breaches through the first kiln wall also must have been arched over, but only in the west drawholes was there any evidence of this. There the arch was still in place when excavation uncovered the top of the surviving wall. However, when the earth surrounding it was removed the arch collapsed into the empty space of the alcove below. All that was then left in situ were the springers which consisted of four courses of brick forming a stepped slope for the first stone of the arch on each side (Fig. 18). These bricks were laid partly on top of the side walls of the alcove where they faced off the jagged edge of the breach and therefore provided a terminus post quem for construction of the arch. It is unlikely that these arches were built at the same time as those over the alcoves since, although they were at the same level, there was no bond between them.

From the above evidence the following construction sequence for the drawholes and alcoves can be offered with some confidence.

1) Excavation of passageways through the hillside on the north and west.

2) Breaching the lower part of the first kiln wall in two places.

3) Building the jambs and arches of the drawholes, and the lower part of the first stage of the second kiln wall.

4) Erection of the side walls of the alcoves up to the level of the top of the drawhole openings.

5) Completion of the side walls of the alcoves and the first stage of the kiln wall together.

6) Placing the piles of fieldstone behind the side walls of the alcoves.

7) Construction of the arches over the alcoves.

8) Construction of the arches over the breaches.

9) Packing of earth between the two kiln walls.

10) Construction of the second stage of the kiln wall partly overlapping the arches of the alcoves.

The only stage in the construction sequence that can not be precisely placed is the laying of the field stone sills of the drawholes. It must have been after the erection of the jambs since there is no bond between the two, but there is no terminus ante quem for their construction. Probably they were laid at the same time as the floor of the kiln, which may have been the last stage in construction.

The Southeast Drawhole

The sequence of construction at the southeast drawhole (Fig. 16) was somewhat more complicated because the opening of the first kiln had to be demolished before the new drawhole could be built.

As noted earlier, all that remained of the opening was the base of the jambs and the brick sill, which were presumed to have survived the modifications because they were hidden below the existing surface. Everything above was demolished to make way for a wider approach to the drawhole. Removal of the jambs, and therefore of the arch of the opening of the first kiln, probably also involved demolition of the arch over the arms, but since nothing of this arch survived it is not possible to be certain.

Following the demolition of the opening, the next stage in construction was the laying of the first two courses of the kiln wall beneath the sill. Probably this was done to bring the base of the jambs up to the same level as the others, since the floor of the first kiln on which this was being built was lower at this point than elsewhere.

The next task was the erection of the brick jambs with an offset on the outside. This offset was probably designed as a door check for a removable door that served to control the flow of air into the kiln.

The arch of this drawhole was different from the others since it did not have supporting iron bands (though these may have been removed), and the stones of the arch were laid on end rather than on their sides. With the sill in place, the opening was the same width as the others but approximately 6 in. higher. Since the side walls of the alcove abutted the back of the kiln wall, they must have been built later, as in the other alcoves. The demolition of the jambs of the first entrance exposed the core of the wall behind, so the side walls were built, as in the other alcoves, as a one-course-thick facing between the two kiln walls and over the jagged edge of the core, but in this case continuing outward to bond into the area of undisturbed facing on the arms. The alcove was further widened by changing the direction of the north sidewall of the alcove so that it joined the wall of the second kiln clear of the drawhole (Fig. 9). As with the other alcoves the main thrust from the earth packing was taken by piles of rubble-stone behind the side walls. No doubt there was also an arch over the alcove resting on these stones, but nothing of this remained when excavated.

16 The southeast drawhole of the second kiln. There are no iron bars supporting this arch.

Presumably, the construction sequence continued in the same way as for the other alcoves, possibly ending with the reestablishment of an arch across the arms creating an alcove 9 ft. long. Finally, the floor of the alcove was raised one foot by the addition of a deposit of red, stony clay/loam, C horizon material. This resulted in a floor level 1.3 ft. below the sill of the drawhole. On top of this there was a thin spread of lime and above that the alcove was filled with rubble collapsed from the arches and walls. Approximately 6 in. from the drawhole, on the floor of the alcove, there was a wooden beam laid crossways with both ends running just under the side walls. Its function is uncertain, but it may have been a joist for a wooden platform in the alcove and passageway.

17 Iron bands supporting the arch of the west drawhole.


The North and West Passageways

The north passageway could not be fully excavated because it ran under the present, and only, access road into the fortress. Excavation, therefore, had to stop approximately 5 ft. short of the road to avoid subsidence. Consequently, only 6 ft. or so of the passageway was uncovered. The floor of the passageway was found at an elevation of 9 ft. above sea level. A wooden platform covered the bottom of the passageway but did not extend into the alcove. Although almost completely decomposed, it was possible to detect in the wood a pattern of planking running parallel to the sides of the passageway, resting on joists anchored by dovetail joints to sleepers along both sides. Mortices were cut in the top of the sleepers to take upright posts only the stumps of which survived. On top of the wood were scattered deposits of lime that had probably been dropped when the kiln was being unloaded.

The west passageway was similar but the sides and the wooden platform were much better preserved and were more easily accessible, except at the outer end where a modern building had been constructed with its foundations dug down almost to the floor level of the passageway.

18 Brick springer of the arch over the breach for the west alcove.

The passageway was 9 ft. wide at the alcove and 15 ft. wide at the other end of the wooden platform that occupied most of the floor space (Fig. 19). This floor was at an elevation of 10.2 ft. above sea level. 9.8 ft. below modern ground surface at the kiln wall and 7.75 ft. below at the outer end of the platform. Originally the depth of the floor below surface level would have been greater, but since the original height of the bank around the kiln was unknown, the exact depth could not be calculated.

The length of the passageway was also not calculable because the foundations of the modern house cut into the outer end. However, the modern ground surface near the house sloped away toward the south and the slaking pits (see Slaking at Louisbourg), so the passageway probably was approached from this direction. The floor of the passageway continued some way beyond the end of the wooden platform, but there was nothing to indicate the floor level except the rising junction of the undisturbed subsoil and the loose fill on top.

This passageway had a planked floor 26 ft. long, gradually widening from 8.5 ft. near the alcove to 14 ft. at the outer end. The framing of the floor consisted of sleepers along both sides and six joists dovetailed into them at 4 ft. intervals. The sleepers each consisted of three lengths of 10 in. by 10 in. wood, 7 ft., 12 ft. and 7 ft. long. The outer end of each sleeper had one-half of a shiplap joint with two holes cut vertically through it, but no indication of a joist joining the two sleepers. However, it is possible that the wood used in this floor was previously used elsewhere, which would explain this and other aberrant features such as notches and holes found in the surface of the wood. The joists were also 10 in. by 10 in. and their dovetailed joints were held in place by two treenails driven through the lap. Remains of floor planking lay on the joists. This planking was laid parallel to the sides of the passageway. The width of the planks varied, those in the centre being over one foot wide and those along the sides being 10 in. wide. In the middle of the passageway 10 planks were needed to cover the width of the floor. Because of the wedge shape of the passageway, the centre planks had a slight taper toward the kiln. No complete planks were found, but the longest surviving piece was over 8 ft. long.

19 Part of the wooden floor of the west passageway.

Mortices for tenoned uprights were cut in the tops of the sleepers at slightly irregular intervals, but averaging 2 ft. centre to centre. These were 12 in. long and 2 in. wide and were set near the inner edge of the joists. Some of the mortices still had the stumps of tenons in them, though the uprights themselves had completely decomposed with the exception of one very fragile piece. The last mortice on each sleeper, about one foot from the outer end of the platform, contained the remains of a slanting post for a sloping end to the wooden revetment of the passageway. These posts, and presumably the rest of the framing, were 12 in. by 6 in. It is not certain why the mortices were cut near the inner edges of the sleepers, but such an arrangement would have allowed some batter to the revetment to follow the slope of the earthen sides of the passageway. In some places along the inner edge of the sleepers, traces of the plank sheathing set on edge were found.

20 Section through the west passageway. 1, turf and humus (topsoil); 2, dark brown organic layer (buried turf line? original bank surface); 3, light brown sandy loam, traces of organic matter near base (fill behind wood revetment); 4, black organic matter (profile of decomposed wood revetment); 5, clay-loam, patches of organic matter, burnt in places; 6, mass of beach gravel, rocks; 7, black organic matter mixed with sand; 8, planking on floor of passageway; 9, yellow, hard-packed, stony, sandy loam, weathered C horizon (vertical edges represent sides of passageway). (click on image for a PDF version)

The fill of the passageway consisted of a loose mixture of stone, sand, gravel and loam which was the unconsolidated, redeposited version of the weathered, yellowish surface of the C horizon through which the passageway had been dug (Fig. 20). Most of the fill was probably thrown in from the banks by the French, when they were razing the kiln during the second siege. Thus, on the floor of the passageway there was a large deposit of boulders, presumably from the upper part of the kiln wall.

The sides of the passageway could be easily distinguished from the fill since the former were very compacted, almost concreted. The trench sides seen in Figure 15 are the actual passageway sides, which accounts for both their unevenness and their uprightness. The remarkable preservation of the sides of the passageway must have been due to immediate filling; if it had been left open for even one winter the sides would have eroded to a shallow slope.

The Southeast Passageway

Most of the features of the southeast passageway have been discussed in connection with the first kiln, few modifications being necessary for the second. Raising the floor of the alcove and passageway by approximately 12 in. blocked off the drain leading from the passageway which was presumably no longer considered necessary now that the floor level was above the water table.

The other major modification was the addition of a dry-stone wall across the south end of the passageway. This wall abutted the side walls of the passageway and sat on top of the raised floor. The rubble from the passageway walls was resting against this wall, so it must have been built before the destruction of the kiln. Although the wall obviously must have belonged to the kiln, its function is rather obscure since it blocked off access to it. However, as Figure 9 shows, the wall was built with a separate centre section about 2 ft. wide. Two vertical joints can be seen, and behind this centre section of the wall the old ground surface was found to slope gradually upward, whereas behind the wall on either side there were banks of earth. This section of wall, therefore, was removable. Probably when the kiln was not in use, the entrance was blocked with this dry-stone wall.

21 Floor of the second kiln.

The Floor

The floor of the second kiln was unique, there being no parallel in the available historical sources. It indicated a radical departure from the firing method used in the previous kiln.

Occupying most of the floor were the remains of a circular field stone pillar 5 ft. in diameter (Fig. 21). Leading from the pillar were three ridged arms extending to the wall of the kiln midway between each of the drawholes. This arrangement created stone-lined, arc-shaped depressions 5 ft. long and 1.8 ft. wide immediately inside each drawhole. There were soot marks on the sides of these hollows that reached a point above the surviving remains, indicating that originally the pillar and arms were approximately the same height as the top of the arches.


While in detail the second kiln appears to be unique, it has a definite generic relationship with the running kilns of Flanders and the Rhône valley. Points of similarity include the double wall (which may have been the specific reason why this kiln was built within the first), the inverted cone shape, the three drawholes, the iron bands supporting the arches of the drawholes, and the covered passages or alcoves leading to them. Specifically related to the Rhône valley kilns are the materials used to build the kiln — local fieldstone set in mortar — and the pillar occupying the cendrier. The major differences include the arms radiating from the central pillar of the floor and the absence of the loading ramp. Both these differences can be explained by examining the specific circumstances of this kiln. First, the kiln was basically subterranean and therefore needed no loading ramp since the banks and the hillside would serve for this purpose. Second, the kiln illustrated by Diderot (Fig. 5) had a floor only 2 ft. in diameter which could easily be spanned by iron bars. In contrast this kiln was over 7 ft. in diameter at floor level. Iron bars spanning this gap would have had to be massive to take the weight of the load and resist the buckling effect of the heat. To circumvent this problem the builders provided a central pillar and radial arms to support much smaller grille bars above each drawhole, and thus still retained the same method of operation as shown by Diderot. The load would be placed on top of the grilles which could be removed when drawing the lime. In addition, the central pillar would help to funnel the lime to the drawholes as in the Rhône valley kilns. A minor specific difference is the absence on this kiln of horizontal cross-bars at springer level in the drawholes, but this could easily be compensated for by varying the arrangement of the bars of the grille.

A clue exists that may explain why this particular type of kiln was built at Louisbourg. In 1752, Rouille, the Minister of Marine in France, wrote to Franquet, the king's engineer at Louisbourg, that he was sending him the designs of kilns from the Tournay, Anjou and Rhône regions of France.1 Perhaps one of these designs was the inspiration for this kiln.

The second kiln, therefore, represented a departure from the earlier one not only in design and capacity but also in method of operation. The change from a relatively simple periodic kiln to a sophisticated continuous kiln, exhibiting evidence of ingenuity on the part of the builders, strongly suggests that whoever built the second kiln was well versed in the art of lime-burning. This is in obvious contrast to the previous attempts at building lime-kilns at Louisbourg, about which numerous records remain attesting their poor quality, restricted capacity and functional inefficiency.

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