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October 4 - October 10, 2010

The façade of my late-19th-century, cast-iron office building has been coated several times, most recently in the 1960s. The paint is faded and delaminating, and I want to remove and replace it. How do I assess the condition of the cast iron and coating, repair weakened areas of the cast iron, and prepare and recoat the surface?


Selected Answers

From Richard McLaughlin of Marco Group International on October 12, 2010:
Although all three of the prior answers have good elements, they seem to fail to answer some of your question. First, you need to address the condition and adhesion of the coating. You can do this with several tests, but one of the easiest and most reliable is the simple “Tape Test”, or ASTM D3359-09e2. I would do this procedure at several locations on the building. To do this test, you simply have to take a razor or X-acto-type knife and make several slices through the surface to the substrate at uniform intervals that can be from 1 to 6 cm apart. Next, you repeat the slice pattern at 90 degrees to the first set, making a cross-hatch pattern. Now, take a piece of highly adhesive tape, I prefer rubber-based adhesive duct tape, and rub it down over the sliced surface. Pull up the tape in a rapid motion while maintaining a 90 degree angle to the surface. The resulting pattern of adhered and missing paint, when compared to the ASTM chart, will tell you how well or poorly adhered the coating is. KTA Tator or Paul N Gardner carry kits that include everything you need to do this test. Once you know the condition of your coating, a proper removal process needs to be put in place before you can properly access the condition of the cast iron under the multi-layer coating. As has been mentioned, there will be surface contaminants, and most likely, rust and lead will be present that needs to be addressed either before or during the coating removal process. Media blasting is not out of the question, but will require a high degree of technical capability and the use of some very expensive equipment and supplies to create an environment that is safe to the public and the worker. Negative air, HEPA filtration, dechlorination, decontamination trailers--these are just some of things to be considered when setting up a blast job like this. Chemical stripping might just be the method that works best in a urban environment. Either way, to save you time and give you peace of mind, I would consider requiring a contractor to have the SSPC QP-1 and QP-2 certification before bidding on the job. Companies with these certifications have gone through a very stringent process that confirms their competence on general practices as well as the skill specifically required for the abatement of hazardous material. As each area is stripped and cleaned down to bare metal, or as close as you can practically get, you can then evaluate the cast iron substrate. You will have to consider several elements when deciding your rehabilitation options. If an area is completely rotted, you will need to replace it. Normally, welding would be the method of choice. However, by nature, cast iron is difficult to weld on. It can be done, but again you need a qualified person to do the work. You might consider a bolt or rivet method for attaching replacement parts. Areas that are not quite so dramatically damaged may just require the use of an epoxy or polyester metal filler to repair the surface and restore the original look. Decisions on the method and type of repair should be discussed with your coatings contractor. If you follow my advice and hire QP-1 certified contractor, they will be quite knowledgeable about your options here. Fianlly, as for recoating, all the major coating manufacturers offer a line of quality products that range from a DTM (direct-to-metal) to a multi-coat system that will not only look good, last a long time if properly applied, but will offer you greater protection for your building then was ever available before. I would contact several of these manufacturers and talk with their technical department about what you are doing. You will find a great deal of help there and it is offered for free. Richard McLaughlin - Marco

From regis doucette of Chlor*Rid on October 8, 2010:
I would also consider a wash down with an acidic soluble-salt remover prior to primer being applied, since the building is probably exposed to industrial air pollutants being in a city that would include sulfates from fossil fuels. If located in the north, the deicer salts would also contribute to issues. Regardless of location, the US Government deposition maps show soluble salts being deposited from normal rainfall. One issue here is to prevent inter-coat adhesion failures because of surface salts.

From Lubomir Jancovic of MSPLUB Inc. on October 7, 2010:
You can use coats of metallic zinc and of aluminum, which wil protect the surface of steel up to 70 years with no other maintenance. You can use combustion wire spray system.

From remko tas of Futuro SRL on October 5, 2010:
On this old builing, lead-based paints may have been used; therefore, abrasive blasting or ultra high pressure water jettingshould probably not be used. A chemical paint stripper will probably do the job, and it is easy to keep the jellyish leftovers together and dispose of it correctly. Any tightly adhered layers of base paint that were not removed by the paint stripper could stay and serve as a base. Before painting, the surface should be washed to remove leftovers of the stripper,then sanded by hand and recoated. Weakened or rusty areas will requiere a more thorough surface preparation,such as power sanding to bare metal. In these places a good primer should be applied before the topcoat.

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Tagged categories: Cast iron


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