The church: structure and materials

CHAPTER II. An examination of the structure of the church and the materials used therein from time to time.

The church is remarkable neither for constructional skill, nor enrichment of detail. Surrounded of old by marsh land, the building materials nearest to hand did not admit either of vigorous treatment, or delicate ornamentation; and it is surprising that in such a position, and built with such materials, the walls are as sound and the structure as secure as it is.

The chancel and aisles may be said to be built of chalk, flint, and ragstone rubble faced chiefly with thin coursed ashlar built with little or no bond. Even the brick walls of the nave are constructed largely of chalk & rubble. The mortar, used lavishly in the construction of the walls, is generally of excellent quality, that in the lower bay of the tower especially so. It is mottled in appearance, this being occasioned by the large quantity of chalk mixed with it, and it is exceedingly tough. It is well that it is so, for on the soundness of the mortar depends the length of life of the building. The chalk throughout is perfectly dry & sound, and is occasionally found in roughly squared blocks; but as a general rule this is not so. In a very few instances during the recent restoration, chalk was found on the external face of the wall, but was then very much decayed.

Earlier Brickwork

The earlier brickwork is of good quality. A curious feature of many of the red bricks in the eastern gable and elsewhere, was the large number of thick broken clay tobacco pipe stems which had been embedded in the walls. The oak timbers in both chancel and nave roofs have practically been untouched until the present restoration.

Speaking generally the structural features of this remnant of mediæval architecture, are (1) the absence of bond in the masonry; (2) the successful employment of chalk in large quantities; and (3) the excellent quality of the mortar.

Nave

The nave is constructed with chalk and rubble, faced with red bricks externally & internally, the latter being plastered. The south wall is a little out of plumb, and the north wall very much so; the latter also bulges outwards considerably. A line stretched taut from the tower end to the chancel end of the wall, reveals the fact that it bulges 8¼ inches outwards in the centre, while it is 7¼ inches out of plumb in its total height for nearly the whole length. The reason for this has been assigned to the removal in 1844, of the ceiling and joists which were said to tie the two opposite walls together. When, however, it is borne in mind that the walls are not fractured, and bear no signs of having gone quickly; also that the ceiling was no part of the original design (being added by the Trustees of Mrs. Coburne in 1702, and removed again in 1844) it will be conceded that the defect is unlikely to be the work of half a century only.

The nave was originally supported upon stone piers of varying size, with a plain chamfered arcading. After many alterations all assumed the present octagonal shape; and it is to these repeated alterations we owe the fact that only two bays are alike, all the others differ both in height and span. The piers are probably a ragstone, though a high authority has expressed the opinion that they may be Hassock. That they are limestone may be assumed. At one of the Restorations referred to in the preceding chapter they were roughened and plastered.

Clerestory Windows

The clerestory windows are of Box ground stone, (fn. 1) some of which having weathered badly, were, at a former restoration, patched & repaired with Roman cement. This coating having become loose in places, it has been found necessary to again repair them; this time Portland stone has been used, together with the best of the Chilmark taken from the hood mould of the "Churchwarden Gothic" window in the chancel.

Oak Timbers

The oak timbers in the roof are of great strength and weight, taking into consideration their number (there are forty-four principals) & the work they are called upon to perform. It is probable that they have remained untouched, until recently, since the day they were framed.

North Aisle

The north aisle wall is built of random rubble, and is surmounted by a red brick battlemented parapet. The wall abounds in chalk, & it is clearly of older construction than any other portion of the edifice. On removing the interior plaster in order to fix the new oak wainscoting, the wall was discovered to be largely faced with chalk, some of which was squared & bedded after the manner of masonry; & even on the outside face several pieces of chalk were found, though greatly perished. Much firestone was also found built in with the flints and ragstone rubble on the exterior face. The firestone was so badly decayed (exposing the interior mortar & chalk to the assaults of the weather and to the attacks of atmospheric gases) that it was found necessary to remove it, and replace with Portland. On the whole the interior of the wall is still fairly sound, and as long as it remains weather tight no danger is to be apprehended.

While piercing the wall for the new doorway leading to the vestries, an interesting discovery was made. About 5 ft. 6 in. from the floor level was a splayed red brick window opening (fn. 2) with an oaken lintel very much decayed, & a foot above that, built into the wall, was another oak scantling. The inside of the opening, which was 7 ft. 6 in. high by 5 ft. wide, was filled with the remains of 15th century window tracery, mullions, and jambs; very much chipped and broken, but still bearing the workman's tool marks, and on one side a thick coat of whitewash. A portion of a moulded door jamb, some remains of more modern windows and a few small blocks of firestone and chalk, filled up the remainder of the window, which was thickly plastered over. The new doorway is in brown bed Portland.

Windows

The existing windows in this wall are modern and are built of Portland stone of good quality, but mixed here and there with a soft freestone, which, having perished, has been replaced. The mortar used in the construction of this wall was found to be very firm, except where it was open to attacks from the weather through the decay of the outer face. The wall is two feet thick at the present ground level.

Battlements

The red brick battlements were capped with moulded Hollington (fn. 3) and Bath stone coping (the latter probably original) most of which fell to pieces on being removed, and which has been replaced with Portland. The Hollington stones have for the most part been retained.

South Aisle

The south aisle wall is 2 ft. 5 in. in thickness and has a Portland stone facing. A few of the original ragstone quoins still remain at the western end. It was during the recent repair of these that the mason found a few fragments of window mouldings embedded in the thickness of the wall. The Portland stone ashlar with which the battlements are faced, is exceedingly thin, in some instances being not more than 2½ in., backed with loose rubble of poor quality. This has been removed and replaced with sound stone without disturbing the exterior face, except where absolutely necessary. The battlement at the South West angle has been rebuilt. Both aisles have flat plastered ceilings with deal rafters and are covered with lead.

Chancel

The chancel is built of ragstone rubble, coursed externally. There is also much chalk and flint in the interior of the walls. The old mortar is generally of excellent quality, except on the south side, the upper part of which was one mass of rubbish. The east gable has long been covered with a thick growth of ivy, which, though very picturesque, wrought great havoc in the walls. Hundreds of birds made this part of the church their nesting-place, & during the recent renovation several cart-loads of litter were removed from behind the stones of the ashlar face.

The battlements were found to be in so precarious a condition as to necessitate their being practically rebuilt, a very large proportion of the original ragstone ashlar was refixed. The S.E. angle fell during the progress of the work and has been rebuilt. In a mortar joint in the adjoining battlement a copper coin of the reign of George III., bearing the crowned harp and the legend "Hibernia," date 182-, was discovered, proving a partial restoration early in the century.

The corner buttress (fn. 4) at this same angle had no foundation whatever, and was fractured its whole length; the N.E. angle buttress was also several inches out of plumb and was badly cracked for half its length, from the top weathering downwards. Both buttresses have been rebuilt, many of the old quoins being retained in their former positions.

The window on the south side is of good Portland stone. Formerly the outer members were of Chilmark very badly constructed, they are now of brown bed Portland. On the inside, the ragstone relieving arch has been rebuilt & a new key-stone inserted. Immediately above this window, extending from the wall plate downwards and striking off towards the angle of the building, was an old fracture; this was well syringed out and grouted, bond stones being built across both externally and internally. The square headed window on the north side is built of Portland, and the large east window of Bath stone.

The oak-panelled timbers of the ceiling are well-preserved. New oak trusses now replace the old ones, & iron girders carry the wall plates and tie in the walls in place of the former beams, which had so far decayed as to render them useless.

The Tower

The chancel walls are 2 ft. 1 in. in thickness at the present ground level, & are still slightly out of plumb. The red brick gable was seven inches out of the perpendicular and the Bath stone coping was very loose & rotten. The tower, the most important feature of the church, is massively built, being 66 ft. 10 in. high by about 23 ft. 2 in. square; the turret at the south-east angle rises another 10 ft. 3 in. above the tower battlements. At the ground level the walls are 5 ft. 7 in. thick; at the level of the ringers' chamber 4ft. 2 in., and at the belfry windows 3 ft. in thickness. The exterior face is almost entirely of ragstone, but internally firestone is much employed.

The two western buttresses are exceptionally narrow, being about 2 ft. across for a base projection of 4 ft. 9 in., and a height of 47 feet; and have little or no bond into the main wall. In the lower bay of the tower a very great number of the stones are bedded on oyster shells. Until the restoration the upper halves of the N.W. and N.E. buttresses were badly fractured; the former for 6 feet and the latter for 10 feet below their respective topmost water tablings; the latter also bulged slightly. Many of the stones in the buttresses, as well as in the main walls of the tower have the appearance of massiveness; but in many cases a stone which measures over four feet in length on the external face, is but five or six inches in thickness, and occasionally even less than that. To give an example of the loose method of constructional masonry employed in the church—the N.W. buttress had but eight internal quoins in the northern angle & nine in its western angle, for a height of 47 feet; while the S.W. buttress had eleven and five in its western and southern angles, respectively. Practically the whole of the ashlar face above the west window had become separated from the interior rubble, on account of this same looseness of bond. A great heap of litter was taken from behind the masonry here; while the back of the hood mould of the west window was completely honeycombed by the ubiquitous London sparrow.

The upper bay of the tower is built of coursed Kentish rag externally, & rubble internally. The belfry windows, quoins, coping stones, and string course, are in Derbyshire grit. The stone is of good quality; but the mortar is not so good as that employed in the older work, the joints there being much closer and the masonry geometrically accurate & the whole thoroughly well built. The battlements, however, and that part of the turret above the tower do not appear to have been built with the same care.

The N. and S. windows in the Ringer's Chamber had been bricked up for many years; the outside being stuccoed and jointed to imitate stone. It is to this that we owe the preservation of so much of the original tracery. The exterior Portland stone arches belong to a previous restoration.

The fifteenth century mortar in Bow Church.

The following extracts are taken from an Article on "The Chemical Examination of Mortar," by H. F. Hills, F.C.S., which was published in "The Builder" of Sept. 17, 1898.

"The sample of Bow Church mortar taken for analysis was from a joint in the chancel wall, & is believed to have been made when the wall was first erected in A.D. 1480-1490. The joint was in too good a condition to justify penetrating into it to any great depth, but the extreme exterior surface was avoided.

"Comparing the analysis of this mortar with Mr. Hughes' analyses (of mortars from the ancient abbeys and castles of the British Isles) it is found that Corfe Castle possesses the mortar which most nearly approaches it in composition, thus:

"According to Mr. Hughes, the mortar of Corfe Castle is one of the best mortars examined by him, but the above analysis shows that Bow Church mortar is of an equally good quality. It is remarkable that Mr. Hughes did not find as much as 1.5 per cent. of sulphuric anhydride in any of the ancient mortars, whereas Bow Church mortar contained 4.86 per cent. This may have been present in the lime originally used, or partly present in the water used for mixing the mortar, or it may have been absorbed from the atmosphere through the agency of rain water. The sand when separated from the calcareous portion of the mortar appeared to be of good quality, the grains being irregular in size, & for the most part having sharp edges.

"It must be remembered that most of the carbon dioxide, the combined water, and possibly of the sulphuric anhydride, has been absorbed since the lime and sand were mixed. Deducting these three constituents, and calculating the percentage proportions of the remaining compounds, the analysis appears thus:

"The proportions of sand and lime used were probably (roughly) one of sand to one of lime."

The composition of the building stone.

The following article from the "Architect," Vol. LX, p. 146, corroborates the opinion that the stone employed in the original structure was most probably Kentish ragstone:

The Stone in Old Bow Church.

By Harold F. Hills, F.C.S.

"Much difference of opinion has recently been expressed as to the nature and source of the stone used in the construction of the oldest existing portion of Bow Church (1480–90 a.d.), that Mediæval building in East London which since 1896 has remained closed on account of its dangerous condition, and is now about to be restored.

"With a view to gaining, if possible, some conclusive information on the subject, the writer has subjected some pieces of the stone to careful chemical analysis, in order that the composition of a specimen might be compared with the published analyses of the building stones from the various English quarries.

"A difficulty has, however, been encountered owing to the fact that even our most modern text-books publish only a few analyses made sixty years ago for the Royal Commission on the Selection of Stones for the Houses of Parliament, and the solitary analysis of Kentish ragstone and hassock made by Phillips for Whichcord's paper on 'Ragstone' in 1846.

"Careful search through the literature dealing with building stone during the last half-century reveals very few additional analyses, and the comparison cannot therefore be as complete as might be desired.

Nevertheless, the results are interesting, and indicate very strongly that the stone is in all probability Kentish ragstone, as will be seen by the following figures:

"No other published analysis compares so closely with the composition of the Bow Church stone as that of Kentish rag quoted by Whichcord, & although the percentage amount of water absorbed by Kentish rag (taken from Rivington's 'Notes') appears to be less, this is accounted for by the fact that the Bow Church stone showed signs of decay, and as a limestone decays it becomes more porous.

The Effect of London Air.

London Atmosphere

"In order to ascertain whether the composition of the surface of the stone had been affected by the East London atmosphere, some surface scrapings were taken from the same spot in the chancel wall as the sample of stone previously analysed, and it was found the sulphuric anhydride had risen from a mere trace to 7.78 per cent., while the amount of 'volatile matter and combined water' had risen from .05 to 2.24 per cent.

"These results corroborate those of Dr. Voelcker, who in 1864 showed that house soot contains sulphate of ammonia, and that this sulphate of ammonia converts limestone (carbonate of lime) into sulphate of lime, and stated that in the presence of moisture the sulphate of lime 'takes up water of crystallisation, and thereby leads to exfoliation of the stone.' "