Heritage repair, hazards and the record

Much of the forge welding done today is repair: a broken railing in a nineteenth-century terrace, a gate hinge rusted through, a verandah bracket snapped by a falling branch, a scroll knocked off a park fence. The iron is usually wrought iron, made more than a century ago, and the owner or the heritage authority wants the repair to keep as much of the original as possible and to look and behave like it. Forge welding in matching wrought iron is often the best way to achieve that, though not always, and the decision belongs to the repairer, the owner and the authority together. The repair also brings its own hazards, some of them, such as old lead paint, invisible until they are disturbed.

This chapter sets out the principles of heritage repair, compares forge welding, fusion welding and mechanical repair for a broken wrought iron railing, describes the hazards of the forge and how they are controlled, with particular attention to noise, and closes with the shop record and a summary of the book.

Do as much as necessary, as little as possible

Australian heritage practice is guided by the Burra Charter, the charter for places of cultural significance adopted by Australia ICOMOS, whose central principle is to change a place as much as necessary but as little as possible. For ironwork that means repairing rather than replacing, keeping the original iron wherever it is sound, matching new material to old, making repairs that can be identified on close inspection, and recording what was done. A railing with one broken bar is repaired at the break, not replaced with a new railing; a bar whose end has rusted away is spliced with a short new piece rather than replaced whole. The heritage authority’s consent, where the place is listed, sets out what may be done.

Reading the old iron

Before any repair, the smith identifies the iron and how it was made. Wrought iron is recognised by its fibrous structure, which shows in a broken end or in rust that has opened along the fibres like split wood, and by its forge welded joints, scarfs and collars. Cast iron, used for ornamental panels, finials and posts in the same railings, is brittle and cannot be forge welded at all; it is repaired by brazing, specialist fusion welding, pinning or replacement casting. Mild steel appears in later repairs and replacements. Mixing the three is common in old railings, and the repair method depends on which one is broken.

Three ways to mend a bar

A broken wrought iron railing bar can be repaired in several ways, and each has its cost and its effect on the fabric.

Figure 1Repairing a broken wrought iron railing bar, 16 mm square

	Method	Effect on the fabric	Illustrative cost, excluding GST
Forge weld splice	scarf in reclaimed wrought iron, welded at the forge	matches material and method; splice visible on close inspection	about A$240
Fusion weld splice	new piece butt welded with an electric arc	strong; different look; wrought iron's slag can cause porosity	about A$150
Mechanical collar	sleeve or collar riveted or pinned over the break	reversible; visible; no heat	about A$120
Replace the bar	whole new bar in mild steel or wrought iron	loses original fabric	about A$180

The forge weld costs the most, because the panel usually has to come out and go to the shop, the scarfs take time, and the shop must have reclaimed wrought iron of the right section. It gives the most faithful repair. A fusion weld is cheaper and strong, but its look differs, and wrought iron’s slag fibres can make it porous, so the procedure needs care. A mechanical collar adds no heat and can be undone, which some authorities prefer for minor breaks. Replacement is sometimes cheaper than any repair and sometimes necessary, but it removes original fabric. The choice is made with the owner and the authority, and the reasons are written down in the job record, so that a later repairer understands why each method was used.

Matching material

Reclaimed wrought iron is the usual material for forge welded heritage repairs, because new wrought iron is no longer made commercially. It comes from demolished structures, old bridges, railway fittings and scrap yards, and it varies in quality: some is clean and fibrous, some full of coarse slag, some corroded through. The shop tests each batch with a sample weld and a nick-break test, as Chapter 7 described, and keeps it sorted by section and quality. Using mild steel to repair wrought iron is sometimes acceptable to an authority, but mild steel corrodes differently and can look different after painting, so the choice is recorded.

Working on site

Some repairs cannot go to the shop: a bar set deep in a stone coping, a gate post leaded into a pier, a balcony bracket that would need scaffolding to remove. Forge welding on site needs a portable forge, usually gas, an anvil or heavy block, and space to work, and it brings the forge’s fire and fume to a place that was not designed for them. Hot work on site needs the owner’s permission and, on many sites, a hot work permit, a fire watch during and after the work, and screens to protect the public and the building’s fabric from sparks and scale. Where those conditions cannot be met, a mechanical repair in place, or a fusion weld under controls, may be the better choice, and the reasons are recorded.

Finishing the repair

A repair is not finished until it is protected. Wrought iron resists corrosion well when painted, but the repaired area, stripped bare and heated, needs a paint system suited to old iron, applied soon after the work so that rust does not start under it. The shop cleans the repair area of flux residue and scale, which hold moisture and start rust, primes it the same day, and finishes it to match the surrounding work or as the authority directs. Where a mild steel piece has been used, the shop records it, because it may weather differently from the wrought iron around it and need watching at the next maintenance.

Old paint and lead

Most heritage ironwork carries many layers of paint, and older layers often contain lead. Heating lead paint, by the forge or a cutting torch, releases lead fume; grinding or blasting it releases lead dust. Both are serious hazards to the smith and anyone nearby, and lead work is regulated under the work health and safety laws, with requirements that can include health monitoring when the work is lead risk work. The shop’s practice is to strip paint from the repair area chemically or by careful mechanical methods with dust controls before any heat is applied, never to burn it off, to keep stripped paint waste contained and dispose of it as the regulator requires, and to test old paint for lead when there is doubt.

The forge’s hazards

A forge combines heat, fire, hot metal, heavy tools, fumes and noise in a small space.

Figure 2The shop's hazard controls for forge welding

• Avoid: Burnsleather apron, boots, long natural-fibre clothing; hot work marked with chalk; tongs, never hands
• Avoid: Fireclear of flammables; extinguisher and fire blanket at the forge; fire out and checked at close
• Avoid: Carbon monoxidehood and flue for solid-fuel forges; ventilation and a CO alarm for gas forges
• Avoid: Fumesno galvanised or coated stock in the fire; flux used sparingly; lead paint removed before heat
• Avoid: Eyessafety glasses for all; flying scale and flux spit at every weld
• Avoid: Noisehearing protection when hammering; anvil damped; exposure planned (see below)
• Do: ? Visitors and studentsbriefed, protected and supervised; a marked line they do not cross while welding

Burns are by far the commonest injury in the shop: from picking up a piece that looks cold but is still hot, from flux and scale spitting during welding, and from sparks. Hot iron gives no visual warning below about 500 °C, so the shop marks hot pieces with chalk and teaches students to treat all iron in the shop as hot until proved otherwise. Flying scale from the first blows of a weld can strike eyes several metres away, so everyone in the shop wears safety glasses.

Noise

Hammering on an anvil is loud. A hand hammer on a ringing anvil can produce sound levels well above 100 decibels at the smith’s ear, and a power hammer more. The work health and safety regulations set an exposure standard for noise of an eight-hour average of 85 dB(A), and a peak level that must not be exceeded. Above 85 dB(A), every 3 dB doubles the sound energy, so the time that makes up the same daily dose halves.

Figure 3Time at a sound level that equals a full day's noise dose

allowed time = 8 hours ÷ 2^((level − 85) ÷ 3)

At 85 dB(A)

8 hours

At 91 dB(A)

8 ÷ 2² = 2 hours

At 97 dB(A)

8 ÷ 2⁴ = 30 minutes

1. at 100 dB(A): 8 ÷ 2⁵ = 0.25 hours, 15 minutes
2. at 106 dB(A): 8 ÷ 2⁷ ≈ 0.06 hours, under 4 minutes
3. a morning of hammering at 100 dB(A) without protection exceeds a day's dose many times

The arithmetic shows why hearing protection in a forge is not optional. Anvils can be quietened considerably by damping their ring, with a magnet or chain on the body, a bed of sand or a resilient mounting, which lowers the level for everyone in the shop; Cravens’s advice to fasten the anvil firmly to a hardwood block helps both its stability and its noise. Earmuffs or plugs with a suitable rating are worn by everyone in the shop while hammering is under way.

The shop record

Every heritage repair is recorded, for the owner, the authority and the shop’s own learning. The shop’s job card for a heritage job records the place, the item, its condition before repair with photographs, the consent and its conditions, the method chosen and why, the material used and its source, the test welds for that material, the work done, photographs after repair, and the finish applied. Many conservators also mark new material discreetly, for example with a small stamped date on a hidden face, so that a future repairer can tell new from old. The record joins the place’s conservation file and the shop’s own archive.

For all forge welding, heritage or not, the shop records the test welds of Chapter 7, the stock batches, and any failures and their causes. The record is what turns a craft that depends on judgement into one whose judgement can be checked.

Pricing heritage work

Heritage repairs take longer than new work, because the item must be removed carefully, documented, stripped of paint, repaired with matching material, refitted and recorded. The shop prices them from its records of similar jobs, separately from new work, and shows the owner the steps that make up the time. An owner who sees that a single splice involves removing a panel, stripping lead paint safely, testing reclaimed iron and documenting the work understands the price better than one who sees only a number.

Bringing it together

This book began with how two pieces of hot iron become one: clean contact, heat, pressure and a few seconds. It followed that principle into the fire and its reducing zone, the scale that every practice is designed to defeat and the fluxes that turn it into a slag the hammer can squeeze out, the shapes of joints and the stock they need, the race against cooling between the fire and the blow, the metals that weld and those that do not, the strength of forge welds and the spread that limits their use, the chain and rings that were once the forge welder’s main product, and the laminated and clad metals that carry the same principle into art and industry.

The thread through every chapter is that a forge weld depends on conditions that cannot be seen once the weld is made. That is why the smith’s discipline matters: a deep, clean fire, clean stock, a thin flux applied at the right heat, convex faces, a short transfer, light first blows working outward, and test welds recorded honestly. With those, forge welding remains a sound way to join iron for the work it suits, and the right way to repair the ironwork that was built with it.

A failure: the burnt-off paint

This is an illustration. Before the shop’s current rules, a smith repairing an old verandah bracket on site heated it with a torch to free a seized bolt, burning off the paint over a wide area. The paint was later tested and found to contain lead. The smith had worked for an hour in the fume without respiratory protection, and a blood test arranged afterwards showed raised lead levels.

The shop’s rules now forbid heating painted heritage iron before its paint has been tested and, where it contains lead, removed with the controls the regulations require. The cost of testing and safe stripping is included in every heritage quote.

Exercise: a day’s noise and a splice’s cost

A smith hammers for a total of 90 minutes in a day at about 100 dB(A) and spends the rest of the day in quieter work below 80 dB(A). Without hearing protection, how many times the daily dose is that? With earmuffs that reduce the level at the ear to about 82 dB(A), is the dose within the standard? Then, if a heritage splice takes 2.5 hours of shop time at A$95 an hour plus A$45 of reclaimed iron and A$60 of lead-safe stripping, what is its price before GST?

At 100 dB(A), a full day’s dose is reached in 15 minutes, so 90 minutes is six times the daily dose. At 82 dB(A) at the ear, below 85 dB(A), the hammering contributes well under a full dose, so with protection the smith is within the standard, provided the earmuffs are worn throughout and fit well.

The splice costs about 2.5 × 95 = A$237.50 in labour, plus A$45 and A$60, about A$343 before GST, or about A$377 including 10% GST.