ornamental metalwork

Maintaining Metal Fencing

Even the most durable fences, those made of iron and steel, require maintenance.

By Gordon Bock

Wood may be the most expedient fencing material, but when it comes to surrounding public and non-residential buildings for decades — even centuries — the best blend of beauty, versatility and durability has always been iron and steel. Long-lived as they are, iron and steel fences and railings can't survive on their own, especially against impact damage and their unrelenting enemy, rust. Regular maintenance in the form of surface protection and proper repairs is key, as this short course helps explain.

Robinson Iron restored the historic cast-iron gates and perimeter fence for the National Shrine of the Basilica of the Assumption of the Blessed Virgin Mary in Baltimore, MD, designed by Henry Benjamin Latrobe. The project involved cataloging, removal, restoration and installation of the restored materials. Missing components were replicated by taking impressions of original castings and producing working patterns. Original granite footings were protected during removal and installation. Type 304 stainless-steel fasteners and brass bushings were used. Photos: Robinson Iron

Surface Protection
Left exposed, iron and steel are inevitably destroyed by rust, so the first line of defense for most historic ironwork is to protect it with some sort of coating. Rust — technically the oxidation of ferrous metal — is most often caused by exposure to water and air, but is also the result of salt air, sea water, acids, acid rain, and air pollutants. Oxidation in non-ferrous metals like bronze and copper produces a patina that actually protects the metal from further reaction. Rusting of iron, however, produces a porous film that holds moisture, promoting corrosion until the metal is completely eaten away.

"Oxidation is nature's attempt to take iron back to its original state," explains Scott Howell, vice president and general manager at Robinson Iron, Alexander City, AL. "Oxidation is blocked if we can separate the iron from air and water with some sort of coating." While steel fencing may be ordered factory-galvanized — that is, electro-plated or hot-dipped with a sacrificial shield of zinc — historic iron and steel fencing is typically protected by paint or similar coatings that must be carefully maintained — especially immediately after repairs or installation."

The original historic Smithsonian gates, made of cast iron and true wrought iron (not wrought steel), were brought to Stewart Iron Works in very bad condition. Missing wrought-iron components were replaced using salvaged wrought iron from other historic projects. Missing scroll parts were laser cut in steel plate and finished with shot blast to recreate the appropriate texture. After they were re-assembled, the shiny areas were textured with shot blast to hide weld seams before the final paint. Photos: Stewart Iron Works

Meticulous preparation is critical if the metal is to hold a coating. First, the surface must be cleaned scrupulously free of rust, scale, oil or grease. After chipping away any loose paint or rust, many projects move to low-pressure, dry-grit blasting with particles 70-100 mesh in size at no more than 80 lbs. per square inch. Scaling hammers and needle guns are also effective tools. Wet blasting of any kind is out because it immediately rusts the iron. Where blasting is not permitted or practical, wire-brushing and sanding down to bright metal is an option for repairs and small installations.

After preparing the surface, some projects treat the metal with a rust converter, such as tannic-acid based products that chemically convert the iron oxide rust to more stable compounds. Converter or not, the bare metal must be quickly coated with primer. Traditional iron primers, which contained red lead and zinc, are now unavailable (except for some industrial uses) due to their heavy metal content. They are replaced by alkyd and acrylic rust-inhibitive primers containing iron oxide, zinc oxide and zinc phosphate pigments.

For example, Robert Baird, vice president at Historical Arts & Casting. West Jordan, UT, says his firm has had success using a system based on a zinc-rich primer. "It's about 80 percent zinc powder that comes close to galvanizing," says Baird, "and we follow this with a high-build epoxy intermediate coat that 'locks-in' the primer."

Afterwards Historical Arts & Casting applies a polyurethane topcoat. For coatings applied in its plant, Stewart Iron Works in Covington, KY, uses a proprietary Enviro-coat system. "The primer substrate is similar to powder coating," says Sheri Bomkamp, director of design, "but the cathodic epoxy base coat is electrostatically charged under water, so that the primer seeks and covers all the minute pores and cracks in a casting using capillary action." Stewart Iron then follows this with a polyester urethane powder coating that is compatible with brush-applied urethane wet coatings, "so that the end-user can do their own maintenance in the field later," says Bomkamp.

Whatever the product, never use water-based primers, which will immediately rust the iron, or apply them in fog, mist, or on very humid days. Outside of a factory, primers are best applied by hand-brushing (or roll-and-brushing) so that the primer is worked into the pores and crevices of the metal.

These almost completely destroyed true wrought-iron gates in Brunswick, NY, were restored and reproduced by Architectural Iron Company. The left portion was restored while the right side is a reproduction.

In the field, most fences are finished with two coats of an appropriate (usually alkyd-based) paint product made for metal, such as the industrial maintenance coatings produced by most major paint manufacturers. Glossy sheens are not only historically appropriate, but they also tend to shed dirt and water more than matte sheens before they eventually dull down. Black is the ubiquitous, almost default color for iron fencing. However, don't overlook greens and stone colors that were also used historically and will show more shadows that bring out the ironwork's details.

Repairing Iron
When properly maintained, cast-iron fencing is remarkably strong and durable outdoors, but even this tough metal can require repairs after decades of use, neglect, and sometimes flaws in original construction or installation. Repairs begin with cleaning the fence, then inspecting it for problems. Says Baird, "Doing a class-A restoration typically means taking the fence down and stripping it to a SSP standard — basically bare white metal."

Howell agrees. "When cast iron has a lot of paint build-up, it conceals many of the decorative details, such as incising or leaf patterns," he says. "Paint removal may also reveal more work, such as missing fasteners — typically wrought-iron bolts or pins." Adds Bomkamp, "Paint may also be hiding cracks in cast iron — in fact, the paint may actually be holding the pieces together!"

Though strong in compression, cast iron is brittle, and historic fencing and posts are commonly victims of impact damage, as well as broken connections and missing components. Cast-iron components are also frequently hollow, which means cracks can allow water intrusion, leading to rust or freeze-thaw damage. Plus, many a cast iron fence is the victim of inappropriate repairs. A common example is the hollow newel post or railing that has split after being filled with concrete — a porous material that absorbs water that rusts the thin castings or blows them apart when it freezes.

Cast-iron cracks that are small and non-structural can often be stabilized with pins, epoxy steel, or even polyester auto body repair materials. Bigger breaks, however, are not so simple to repair. "Welding or brazing cast iron to cast iron is tricky and not always possible," explains Bomkamp, "because the metal has to be heated to beet red and sometimes the casting is too thin to do this."

A worker at Historical Arts & Casting primes a section of wrought-iron fencing with Tnemec's zinc rich primer. .

She notes that welding cast iron to other ferrous metals such as steel is more reliable. However, with the right conditions and equipment, such as special nickel-alloy welding rods, a skilled welder can sometimes mend broken cast iron parts — but only for cosmetic purposes. Structural members, such as posts, must be reinforced with steel or replaced altogether.

More problematic is replacing missing parts. While wrought-iron components can usually be individually reproduced in mild steel by qualified artisans, casting iron components is a more complicated process. Foundries that specialize in historic fencing sometimes can provide replacements for common patterns or components, such as finials.

For example, Stewart Iron, which has been in business since 1862, has a large collection of molds. "So when people are looking to replace a historic part," says Bomkamp, "we may have a match — in fact, we may have made the original part in the first place. If not, we have all the facilities to re-create the pattern."

Barring the availability of an appropriate existing mold, casting replacements requires making a new sand mold from a new pattern — a whole other order of project. Since newly cast iron shrinks approximately 1/8-in. per foot as it cools, using an existing piece of ironwork as a pattern produces a slightly smaller component. In some projects, this shrinkage is not critical, but if an exact match is necessary, then a new, oversize pattern has to be made.

When Robinson Iron restored the historic cast-iron gates and fence for the Old State Capitol in Baton Rouge, LA, special consideration had to be given to the historic trees on the site. Their roots are intertwined with portions of the fence. .

According to Howell, one technique Robinson Iron used in the past to account for shrinkage was to take original elements, build them up with polyester resin then make new sand molds from these new oversize patterns. "Today, however, we can laser-scan the original and cut a new pattern in polyurethane," says Howell, "a process that does not even require removing the part from the fence."

Replacements cast from aluminum do not have the shrinkage problem but, upon installation, the aluminum and cast iron have to be isolated or galvanic action will occur. Stainless-steel fasteners and pins are recommended for re-attaching old or new cast-iron work.

Wrought-iron components can still be joined with traditional methods, such as riveting (with countersunk heads, unless rivets are part of the design), collaring (where hot iron strips are bent around abutting members), and hammer-welding (where members are forge melded without the flux used in oxy-acetylene or electric-arc welding). Robinson recommends the use of Type 304 stainless-steel bolts to reassemble restored fencing.

This ornate section of a bronze and wrought-iron gate came from the Dakota apartment building in New York City. It was restored in the Historical Arts & Casting shop in West Jordan, UT. .

However, mild steel often cannot perform like traditional wrought iron. Explains Bomkamp, "True wrought iron is composed of carbon molecules that align in long fibers somewhat like wood grain, which allow it to be worked repeatedly to make forms like scrolls and leaves." By comparison, she says wrought or mild steel, today's substitute, is composed of lots of random individual molecules that can be similarly worked up to a point. "This makes it act kind of like a paper clip; after you bend it a few times, it breaks."

Anchoring
Many iron fences start to suffer not from deterioration of the fence itself but from failure of the anchoring, typically into some sort of masonry. Where the fence or railing is anchored in stone — customary for exterior stairs and urban fences — the fence post or newel stanchion is traditionally "lead-set" — that is, placed in an oversize hole and filled with molten lead.

Howell says that, given the ever increasing concerns over environmental lead, Robinson Iron prefers instead to anchor with epoxy adhesives, such as the products made by Hilti anchoring systems. Either way, post and stanchion ends should be rust-proofed, and once set, the filler should be detailed to shed water, not collect it in the hole. Any moisture that finds its way into the buried iron — especially if the anchor hole creates a little reservoir -- will cause rust jacking that can spall or split the stone.

Many a cast-iron newel post is anchored by a central threaded rod that is okay where it enters the stone, but leaves the newel wobbly nonetheless. In these cases, tightening the nut or finial at the top, usually with gentle applications of penetrating oil, wire brushing, and a little heat from a torch, will often pull the newel back into place.

In contrast to wood fence posts that can be set directly in soil, freestanding iron fence posts must be set in concrete footings that extend below the frost line in order to withstand winter heaving. As Baird notes, "The key to ironwork maintenance is eliminating the conditions that caused the problems in the first place."


Gordon Bock, writer, architectural historian, technical consultant, and co-author of The Vintage House (www.vintagehousebook.com), lists his fall workshops and seminars at www.gordonbock.com.

 

Select Suppliers

Architectural Iron Company Milford, PA
www.architecturaliron.com

Historical Arts & Casting
West Jordan, UT
www.historicalarts.com

Robinson Iron
Alexander City, AL
www.robinsoniron.com

Stewart Iron Works
Covington, KY
www.stewartironworks.com

Building Technology Library

The online Building Technology Heritage Library from the Association for Preservation Technology International (APTI) is a collection of trade literature from the 19th and 20th centuries. It includes a number of catalogs on historic fencing. These architectural and construction trade catalogs and documents provide a rich history of architectural materials and styles. The library was launched in 2006 with a contribution from the Centre for Architecture in Montreal, and it continues to grow as new documents become available. For more information, go to http://archive.org/details/buildingtechnologyheritagelibrary.

Iron Fencing at a Glance

Wrought Iron
An ancient material — but effectively no longer made today — wrought iron is iron ore refined with a low-carbon content (no more than 0.35%). Compared to the higher carbon content of cast iron and steel, wrought iron is close to pure iron, which makes it very malleable and readily formed into characteristic scrolls, twists and leaves.

It is also easy to weld and less susceptible to rust that other ferrous metals. Explains Don Quick of Architectural Iron Company in Milford, PA. "Today what is commonly called wrought iron is actually mild steel bars that are heated, 'hammered,' and bent into shapes (frequently by machines) to mass produce scrolls, twisted bars and the like."

Wrought-iron fencing and railing has its roots in Europe, and though iron was available as early as the mid-17th century from small forges like Saugus Iron Work in Saugus, MA, (established 1644, now a National Historic Site), much was also imported. By the 18th century, domestic wrought-iron fencing was more common in cities such as Charleston, SC, which produced acclaimed fences and railings by three German smiths.

At the turn of the 20th century, when steel had eclipsed iron as the dominant architectural metal, wrought iron enjoyed a rebirth in unmatched popularity and creativity. The revival was propelled not only by the rise of the Colonial Revival and Arts & Crafts movements, but also by one of visionary masters of the ironwork craft: Samuel Yellin.

Cast Iron
An iron-carbon alloy known for centuries, cast iron did not take off as building material until the invention of the hot blast furnace in England 1824, and the switch from charcoal to coke and coal as a forge fuel. In contrast to wrought iron, cast iron cannot be hammered, twisted or otherwise fashioned by an artisan; and though good in compression, to have any strength individual pieces had to be beefy and therefore quite heavy. However, since cast iron products were cast from molds, they could be mass produced rapidly and economically in identical forms and unlimited numbers, making it the marvel material of the Victorian age.

While cast iron could not duplicate the lithe, muscular forms of wrought-iron fencing, it could mimic the surface decorations and general shapes and outlines of objects from houses to statuary to furniture. Moreover, because it could be mass produced, cast iron made possible the order-by-catalogs products of famous foundries, such as the Wood & Perot Iron Foundry of Philadelphia that shipped cast-iron fencing and railings all over the country, bringing affordable fencing to wide ranges of the population, and becoming an iconic part of cities like New Orleans.

Steel
Steel, which is generally iron with not more than 2% carbon, began to displace wrought and cast iron for fence-making at the end of the 19th century along with advances in mass producing the metal. Steel ushered in a new fence type — the composite fence made of steel and malleable iron — composed of light-gauge wire that was zinc-galvanized for protection, machine woven for rapid production, then shipped in rolls for installation on posts.

Such fencing — the precursors to the chain-link fence so ubiquitous today — were widely marketed by mail-order giants Sears Roebuck and Co. and Montgomery Ward and used on farms and households alike. The popularity of metal fencing, from iron to steel woven-wire, continued apace well into the 20th century until two world wars took their toll.

World War I saw many old cast- and iron-wire fences torn up and melted down in scrap drives — the historic fence surrounding Boston Garden being a famous example. During World War II, all fence production was shifted to strictly utilitarian types, spelling the end of decorative designs for most major manufacturers.