ACPA - Cemetery Ironwork Good Practice

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Cemetery Ironwork Good Practice - Part 2

The single best protection of ironwork is maintenance -- and this revolves around painting. In fact, many suggest that ironwork should be repainted every five to 10 years, or at the first signs of rust. Rust happens anywhere that you have iron, water (or moisture), and oxygen. Eliminate one of the three and you've solved the problem -- but of course this is impossible; while we can't prevent rust, we should strive to retard its return.

The first step is to evaluate the corrosion problem -- determine what is causing the corrosion. Once you figure out the problem, you may be able to attack at least part of the problem through repair and preventative maintenance.

Joints are especially vulnerable locations in ironwork -- water will be drawn into these spaces by capillary action and corrosion can be very severe. Another problem area is where cast and wrought iron come into contact since this creates corrosion from electrolytic action. Often you'll see the cast iron top rail laid on a wrought iron connector being pushed up and split by corrosion. Simply sealing this joint doesn't eliminate the problem -- it only seals in the moisture and corrosion continues unabated. It necessary to stabilize (and often remove) the corrosion -- only then can the joint be sealed (red lead putty was originally used, but today a clear silicone sealant is usually more practical).

Another problem occurs when ironwork is anchored in damp stonework. As the iron rusts it expands to many times its original size, exerting pressure on the stone and ultimately shattering the stone. Often the ironwork was mounted into the stone using molten lead -- this combination, too, can cause serious corrosion. Another, even greater, problem is found when iron was mounted using molted sulfur -- this causes very rapid corrosion. Consequently, sometimes the first step in painting is making necessary repairs to help minimize future problems -- and a conservator can advise you on these issues.

When problem areas are addressed, its time to think about painting. But first you must deal with the existing corrosion. Just as in other painting jobs the hard work comes in preparation -- not painting. There are essentially two options -- remove the corrosion or convert the corrosion into something stable.

Removing corrosion can be a daunting task, especially on something as detailed and intricate as an iron fence or gate. Hand preparation using a wire brush is good at removing bulk corrosion, but it is hard work and leaves much corrosion untouched. An alternative that many select because of its ease is abrasive cleaning. In general, conservators do not recommend this approach. While cast iron is pretty hard, wrought iron is softer and the surface can be easily roughened. Using abrasives also removes the mill scale, which is iron's natural protective coating. If for some reason abrasive cleaning is essential its advisable to use a soft abrasive, such as ground shell, at a low psi. Final working pressure is not likely to exceed 60-70 psi with a working distance of at least 12 inches.

Once cleaned of corrosion it is critical that a rust inhibitor be applied quickly. There are a variety of suitable primers -- what is more important than the choice is that two primer coats be applied. With one primer coat it is almost impossible to produce a continuous film without pinholes. A second coat is essential -- and works better than a second topcoat since it is designed to inhibit rust from breaking through the final paint coat.

Your paint should be an alkyd rather than latex and should be designed for use with the primer you have selected. Some suggest the use of new generation epoxy paints, which are very durable. They are very difficult, however, to remove and should not be your first choice. In no case should the paint be applied thickly -- this obscures detail and does not appreciably lengthen the lifespan of the paint. In fact, thick paint can chip more easily than a thinner coat. An appropriate color, lacking any other historic evidence, is flat black. Gloss enamels should be avoided.

Another option is the use of a rust converter. These paint-like products are applied directly to rusty metal after only minimal surface preparation -- using light scraping and degreasing. Converters stabilize the corrosion, converting the rust into a more stable chemical. A common formulation is tannic acid, that reacts with rust to form a bluish-black ferric tannate, combined with a polymer to consolidate the rust. The benefits of a rust converter go beyond ease of use -- it is virtually impossible (even with abrasives) to get into every crack and crevice of ironwork -- but a liquid converter helps ensure that there are no hidden rust pockets. The Canadian Conservation Center tested a range of products in 1992, finally recommending three. Unfortunately since that time two have been replaced by untested products. The one product still available is Conquest, distributed by Liner Rolpanit <liner@on.aibn.com>. The other two include Rust-Oleum's Rust Reformer and Corrosion Control Industries <http://www.neutrarustinc.com/index.htm> CCI products (Neutra Clean, CCI 921, and CCI Flex Coat). Remember that after conversion it is still critical to use an appropriate topcoat, following the same instructions as offered above.

(Part 3 - continued on following page)

Chicora Foundation, Inc., PO Box 8664, Columbia, SC, USA, 29202, 803-787-6910

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