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Steel Finishes Study For Wellesley College Multi-Faith Center, Worship Wall

Peter Curry
18 January 2007

The purpose of this study is to explore different methods of finishing steel that provide a durable, environmentally friendly and cost effective finish for steel fabrications in an interior environment. Aesthetic goals include challenging the traditional notion of what constitutes a "blackened" finish by testing alternative mechanical and coating finishes in combinations which can be easily reproduced. The study grew out of the decision that traditional steel blackeners used in previous KT projects are too toxic for the environmental sustainability goals set for the Wellesley project. Alternative finishes include non-acidic steel patinas formulated from dye-oxides, tinted metal sealing waxes that are applied hot or cold, a series of lacquers and clear coat paints/sealants and linseed oil. These different categories of finishes were used in combination except for lacquers with waxes, since both of these are final top-coat sealants for metal. The finished steel fabrications at the Wellesley Multi-Faith Center will be made from hot-rolled steel profiles. Traditionally steel blackeners are applied to cold-rolled steel because its surface is raw and unprotected, therefore chemical reactions incited by blackeners and patinas occur instantaneously on application. In consequence of this the project determined to focus on hot-rolled steel both for its aesthetic qualities and the protective properties of its mill scale. The decision to express the rawness of hot-rolled mill scale as a finish then placed special emphasis on finding a clear top-coat that would preserve the desired finish and be durable in the field. Surface preparation is a critical part of the finishing process for steel for cleansing the material of dirt that could undermine the integrity and quality of the finish and for providing a desired aesthetic effect. Preparation may be as simple as "washing" the mill scale surface with solvents to dissolve greases or it can be done mechanically, which can produce a variety of effects depending on the method used. Considering the objective of this project to express the mill surface of hot-rolled steel, a fine Scotch-Brite pad was used to prepare the steel for top-coating. The Scotch-Brite pad was selected over other mechanical processes because its finished appearance is even; it creates a "machined" look. The project tested all finishes on both hot-rolled sheet steel and hot-rolled stock (1/4"x2"). As noted previously the sheet was mechanically prepared for finishing, the stock in this test was not. The samples of stock we acquired were clean and even enough that only solvent cleansing was necessary. However on some of the patina samples the stock was sanded to help the patina knit to the surface.

FINISHES TESTED

Patinas: All patinas that were used are manufactured by Ron Young of http://www.sculptnouveau.com. They were chosen because of the simplicity of their application and because each series of patina available offers a different chemical composition, i.e. acidic and water based patinas. A "patina stain" was also tested which is a concentrated form of the dye-oxides that tint the patina products.

1) The Vista Patina Black was the only acidic patina that was tested. It is more patina than steel blackener; it contains black dye-oxides that are combined with acids to create a "transparent" black surface with rusted undertones. Here I steel wooled back the surface to expose the patina color.

2) From left, Patina Stain and Universal Black Patina. These two finishes utilize dye-oxides to color the steel sheets. Neither of them create a true patina, they do not oxidize the metal in any form. They simply lay on the surface of the steel. The Patina Stain is the concentrate and the Universal Black Patina is a diluted form of the stain. Initially the Universal Patina appeared to be an unstable finish, it wiped right off with a paper towel, however with a coat of lacquer it held firm. The Patina Stain sample proved to be unstable with and without the lacquer.

Wax Sealants:

The waxes tested in this project were acquired from two suppliers Sculpt Nouveau and Art Research Enterprises, www.thinksculpture.com. The waxes tested from Sculpt Nouveau are formulated as final coat sealant waxes that can be applied cold or hot depending on preference. The Dark Wax from A.R. is specified for hot application however in this study it was applied cold, in an attempt to simplify the finishing process.

3) The Clear Wax and Black Wax from Ron Young.

4) Dark Wax from A.R. which was developed as a hot wax metal sealant. Hot waxing is a process of sealing metal for exterior protection by heating the surface of the metal with a large propane torch and stippling the wax on to the metal surface with a brush or fine rag. The wax melts on contact with the hot metal and knits into the surface providing a durable layer of protection.

Clear Top-Coats:

Five different products were tested in this category for appearance, eco-friendliness, durability and quality of touch up refinishing. In selecting products I focused on sealants that could easily be sprayed and that had a long pot life. This limited us to lacquers, paints and urethane sealants. Each coating sample below is shown with a abrasion-repair test sample.

5) Permalac and Black Permalac, http://www.peacocklabs.com , are hi-performance lacquers developed for exterior metal application and are excellent for sealing bare metal surfaces. These lacquers are rated for ten years of exterior protection. Permalac VOC:778g/l, Black Permalac VOC:588g/l

6) POR-15, http://www.por15.com , is a rust preventative paint that is intended to be used to stop rust from continuing on already oxidized surfaces. It was chosen because of these properties and was the only product that was found for its intended use. VOC:236g/l
High viscosity made spraying this finish very difficult and resulted in a rough finish.

7) CLEARLOK, http://www.birchwoodcasey.com , is a water based urethane sealant that is specified by the manufacturer as a rust preventative coating for clean surfaces. Note the uneven finish. The finish was sprayed evenly and it moved as it dried.

8) Safecoat Acrylacq Satin, http://www.afmsafecoat.com , is a water based acrylic lacquer and was chosen because of its eco-friendly characteristics. VOC:120g/l. This finish re-oxidized the steel in places it had been previously.