The recent ‘raising of the bar’ in the application of mortar repairs in heritage stone conservation works.

In the September 2012 edition of Discovering Stone, I wrote about the benefits of using specialised repair mortars as an effective conservation measure for historic stonework, (‘Plastic Repair on Stone’, Discovering Stone Issue 22). The workability and excellent performance characteristics of the Lithomex and Jahn repair mortars, in particular, were at that time worthy of comment, and there has been a significant increase in the use of these mortars in recent years as masons discover how good they are to work with.

These mortars are now joined by the equally useful Plastalite stone repair mortar from Westox Building Products. A two-part acrylic modified cement based repair mortar, it is proving to be a versatile and effective product that also has the benefit of being locally manufactured.

Whilst my preference in repairing a stone is for installation of hairline stone indents where possible, there will sometimes be instances where this is impractical. In instances where the mouldings do not readily allow the introduction of a hairline joint, for example; where structural implications may arise; or where the geometry of a particular stone physically won’t allow the introduction of an indent, then the mortar repair, or ‘patch’ as most masons call it, still has an important place as a repair methodology. In repairing carvings and statuary, it is also an especially useful measure. And as masons have become more familiar with the various proprietary products mentioned above, the quality of workmanship has improved significantly in recent years.

The art of patching

It’s a particular kind of mason who enjoys the art of patching. It requires care, dedication, patience, a good eye for colour and, above all, a desire to achieve the almost unattainable goal: the invisible patch.

Former proponents of the epoxy repair – a largely Sydney-centric phenomenon – rested their case for preferring epoxy over mortar-based repairs on the ability to work with a pallet of colours and achieve an excellent visual match for the parent stone. And it was undoubtedly the case that a good colour match, historically, was more readily achieved using the epoxy repairs than the mortar. Ultimately, however, the superior performance characteristics of the mortar repair has displaced the use of epoxy-based stone repairs and, as masons have become better at working with it, some have been achieving outstanding results.

One of the great difficulties in colour-matching a mortar repair with the parent stone arises from the fact that the material is wet when applied and will dry to a significantly lighter colour. This requires the mason to possess predictive capabilities. How light or dark will the mortar be once it has dried? Will it be a good match or, after much painstaking work and waiting for it to cure, will the patch need to be removed and re-applied?

Wetting down the parent stone can be of some assistance in predicting a good colour match of the wet repair mortar, but it’s a far from fail-safe tool. Every mason who has ever undertaken patching duties will have had multiple attempts at getting it right. It can be a deeply frustrating, not to mention economically unproductive, experience. And of course, experience is everything. And the masons most likely to produce patches of a high quality are those whose trials and errors have been numerous.

Some masons have developed a ‘colour chart’ to assist them, manufacturing multiple samples of fully cured repairs each with varying recorded degrees of pigment additives. Figure 1 shows an example, developed by the Traditional Restoration Company. This is one of two such pallets they have created that they use as a guide to establishing likely successful mixes. The initiative shows a commitment to quality of workmanship and is applauded. Even a tool as developed as this, however, cannot replace experience in successfully selecting and blending colours.

On a recent conservation project that I was involved in, a gablet to a coping springer required repair of both its damaged roll moulding and its sunken face panel. The introduction of indents wasn’t considered practical. Figure 2 shows the stone on completion of the repairs, executed using Lithomex by DRP Stonemasonry’s Victor Janecki.

But can you see the repairs? I perhaps ought to feel a degree of embarrassment at confessing that I stood face-on to the stone and thought that the mason alongside me was joking when he extolled the quality of the patches. “We’re looking at the wrong stone,” I thought. “This one needs no repair at all.”
In one of those oddly discomforting moments, it became apparent that he wasn’t joking and that I was indeed looking at two substantial mortar repairs. They were barely visible, even when viewed from two feet away.

Figure 3 reveals the location of the repairs. Care, dedication, patience, a good eye for colour and an abundance of experience, all had come together to deceive the critical eye. These are the moments of glory for the patcher! And these are the instances in which the bar is raised and all patchers should take note. The invisible patch is only a short period of dedication away.

If only it were so easy. Much depends upon the overall visual appearance of the parent stone in the first place. Stonework with a richly developed patina of mottled and generally variable appearance is infinitely easier to patch ‘invisibly’ than largely unweathered stone of a uniform surface colour. With care, though, this too is achievable, as Figure 4 illustrates. Here, the astragal mould at the top of a column has been repaired using Lithomex of a homogenous colour. The result is particularly good.

A great option for conservation of carvings and statuary

On a significant Sydney church spire, a series of carved heads adorning pinnacles at the base had suffered extensive loss of their upper detail. The ravages of sun, wind, rain and salts had weathered the gothic heads away to the point of imminent loss. Some may have been tempted to replace the heads with new carvings, and in some instances, this was indeed appropriate and new heads were carved. But my preference is always to retain as much original historic fabric as possible, and rarely is it more compelling to attempt to do so when historic carvings are at risk. For unlike architectural mouldings, carvings are the individual and unique expressions of men. They are, if you like, the most tangible of architectural bridges to our ancestors.

The faces on these particular carved heads were wrought by men at the height of their trade, in 1850s Sydney, when stone was the quintessential local building material; when elegant university buildings, cathedrals, churches and a variety of other public buildings were rising fast in the still-young colony; when gas-lighters plied their evening trade; when the well-to-do took horse-drawn omnibus rides on Sunday afternoons; when children rolled hoops; when steamers docked from the Motherland carrying mail from home penned six months earlier by their loved ones. When some of their mates headed to the gold fields in pursuit of an easy fortune, these men ­– who walked to work each day carrying their fire-sharpened tools in a leather pouch under one arm and a doorstop of bread and cheese under the other – put their efforts instead into honest work. Using the skills that had, week-in, week-out, brought them the greatest of satisfaction – that gained though creative endeavour. They brought thoughtful, contemplative, even meditative faces to life from hunks of the local sandstone. Those faces, which looked out through increasingly fading eyes onto a very different 21st century life when I first observed them in 2013, could still be saved and preserved for future generations by the careful application of mortar repairs.

Figures 5 and 6 show one of these heads before and after repair. Note that no attempt has been made to guess at and replicate any of the original detail that may have existed in the upper part of the head. The intent is to preserve what remains of the original detail by minimising the further effects of weathering and thus arresting the mode of decay. It is the original detail, and its preservation, that is important.

The skill in achieving this outcome lies not only in the philosophical approach, but also in making the repair as invisible as possible. And here the mason, HBS Group’s David Jakovich, has done an excellent job in blending his pallet of coloured mortars to good effect.

On the same project, a statue of Catholic Archbishop Polding, carved by the eminent French Benedictine monk and sculptor, Father Jean Gourbeillon, had long since suffered such severe fracturing as to precipitate the removal of his head and shoulders in an earlier program of make-safe works. The head was recovered from the parish priest’s office, where it had mournfully sat on the floor for some years, (Fig.7). There was no sign, however, of the Archbishop’s shoulders.

With the head reinstated and secured with stainless steel rods, it remained only to re-form the shoulders and repair the associated localised cracking, (Figs.8 and 9). Here again, the skill of the experienced patcher produced an outstanding result.

Building a repair around a stainless steel armature and carefully blending various colours of Lithomex repair mortar, the mason has restored this statue to its original form and extended the life of this significant sculpture for another generation to come.

The link to Fr Gourbeillon and the rich historical backdrop of his times has been preserved. It provides a good example of how statuary can be conserved in an era when it might too easily have been replaced. There is, in my view, too much to lose in replacing, rather than repairing, such significant elements as these. The skilful use of mortar repairs is a particularly important conservation measure in the preservation of carvings and statuary.

Maintaining realistic expectations

The experience being gained by masons using the latest materials is delivering increasingly impressive results. Pursuit of the ‘invisible patch’ must remain the Holy Grail for patchers. However, it is not easily achieved and this must be recognised by those responsible for quality assurance on any stone conservation project. The masons must always do their best. And, in moments that are particularly satisfying for all, their best will sometimes be exemplary.

Article and photos by Jasper Swann, Stonemasonry Consultant

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