What if you could take a delicate thing like a house shingle and make it last forever, never losing its color? Well, maybe not "forever," but certainly for decades beyond its expected life? Such a technology existed once, and played a nearly-forgotten role in the pageant of American architecture.

Creosote, or more specifically, coal tar creosote, to distinguish it from the nasty and dangerous stuff that builds up inside chimneys from wood fires, was the most popular wood preservative for a hundred years. A 1874 patent mentions in passing a still-older "creosote process" for pressure treating wood, but the first specific recipe for preserving building materials using creosote is found in a 1880 patent for a mix of creosote, turpentine, and paraffin. Several patents were granted in the following years claiming a new or improved formula or process for wood preservation, but the breakthrough was the 1884 patent by Samuel Cabot Jr. for a formula specifically designed for coloring and protecting the "ornamental shingles now so much used by architects." Cabot approached the problem from a different angle than the other inventors, who only wanted to drive preservatives deeper into the wood; his main objective was to find a way to preserve color. The key element in his formula was to use distilled creosote, and twice distilled at that.

Cabot's invention came near the end of the golden age of Shingle Style architecture, so it's unlikely that pioneers such as H.H. Richardson or McKim, Meade, & White ever used his "creosote stain" on their later Gilded Age masterpieces. But as it turned out, Cabot's timing was perfect; the American Queen Anne Style was just about to sweep the nation in the latter part of the 1880s. An interesting "chicken or the egg" question to ponder is whether Queen Anne's popularity was due in part to Cabot's vivid new stains, or whether Cabot owed his success to popular demand for vivid colors on all those new Queen Annes.

By the turn of the century, creosote stain was well established. We know Frank Lloyd Wright used the stuff because his son once fell into a barrel of the gunk. Craftsman architects Greene & Greene certainly relied on it; architect and preservation expert Mark Parry recalls his mentor being told by Henry Greene to specifically use creosote stain for restoration work on their 1908 Gamble house masterpiece ("one carefully applied coat of Cabot’s Creosote Stain #7, allowed to dry two weeks and followed up by another, and it'll last another eighty years"). Was creosote stain used on the shingles for Comstock House? Alas, on this the contract specs don't specify either way. Brainerd Jones indicated only on pg. 8 that both the roof and siding were to be covered using white cedar shingles, but Parry believes Jones must have assumed that the contractor would've used some sort of preservative.

There certainly were other options available than Cabot’s, but many were dolorous; a 1916 reference, "The Chemistry and Technology of Paints" noted that some stains were made by dumping colored linseed oil into crude creosote, sometimes with carbolic acid or kerosene. A 1912 analysis found some contained no creosote at all (their example formula of a "fairly high-grade" stain was nearly one-third creosote oil). A 1930 analysis even found that some were making a homebrew stain with used auto crankcase oil.

Creosote stain earned its reputation for preventing tinted wood from fading. As a 1886 Cabot ad boasted truthfully, "Owing to the strange PRESERVATIVE POWER of the Creosote, wood treated with this Stain cannot decay but simply wears away from the force of the weather." The definitive 1930 USDA report, "The Preservative Treatment and Staining of Shingles" (PDF) performed a 40-month experiment with pine shingles, which found they kept their color well -- although they tended to ooooooze creosote in hot weather.

As for fire protection, creosote stain wasn't great, and several references mentioned that abestine (powdered asbestos) was often added as a fire-retardant. A set of 1916 experiments found creosote stain offered little more protection than paint. The hands-down winner in that test, by the way, was "Penetim" treated wood, which took over nine minutes to ignite -- more than three times longer than any other treatment. Alas, nothing today can be found about this formula, or even the Penetim Manufacturing Co. of New York. (If you know anything, please contact me.)

Creosote stain continued to be widely used until about 25 years ago (see chapter ten in this very informative 1974 Defense Dept. manual on all kinds of roofing). But because of concerns that creosote was a possible human carcinogen, the EPA proposed restrictions in 1984; creosote oil compound hasn't been available for sale in the U.S. since 1988. The danger isn't deemed high enough for an asbestos-like cleanup -- railroad ties, utility poles, and other creosote-impregnated wood is still reused and sold. Creosote is also banned in Europe, Canada, and probably elsewhere.

As an alternative to creosote, the 1930 USDA writer thought that pentachlorophenol (PCP) had "cleaner colors" along with none of the oozing problem. PCP, also known as Penta, is still an option today for pressure-treated wood. But alas, there's never been a formula using anything but creosote that will make shingles last. And last. And. Last.

Creosote may also have gotten a bad rap as a human health risk. The Wikipedia entry reports that a 2005 mortality study of creosote workers found no evidence supporting an increased risk of cancer (no endorsement of accuracy from me until I can read the actual data).

The EPA rulings on creosote is up for evaluation this year and public comments are welcome -- at the master index to docket # EPA-HQ-OPP-2003-0248-0048, there's plenty to read. Among the questions posed by the EPA: "Are there unique uses and benefits of creosote?" Read the guideline for public comments (PDF) and respond by June 16, 2008. Comments can be submitted via regulations.gov; enter the docket number and follow the directions given.

Obl. research note: The gentleman at the end of "Monty Python's The Meaning of Life' who has an unfortunate eating accident after consuming a final ''wafer-thin mint'' was named "Mr. Creosote." You'll NEVER guess what bobs up often during creosote web searching, no matter how much the search criteria is refined.


Newer Post Older Post Home