Reshingling the house was a project we hoped could wait for a year or two, but porch repairs left the southeast corner with exposed new plywood sheathing that needed to be covered before the winter rains. There was no question that we would use unpainted white eastern cedar shingles, as architect Brainerd Jones described in his plans. But without paint, how should the new shingles be protected? In Jones' day, shingles and shakes were often treated with creosote stain, which is now banned. In evaluating the wood preservatives available today, durability was a paramount concern; using a product that needed to be reapplied every couple of years or so would mean that a house this size would be too-often surrounded with scaffolding. Another factor to consider was that white cedar weathers to slate gray fairly quickly, and Candice wanted to keep the live-wood color as long as possible.

Preserving the natural look of the wood meant narrowing the search to semi-transparent stains with UV blockers to prevent fading. To block the ultraviolet range of sunlight, all of these products include trans oxides. More formally known as "transparent" iron oxide pigments, these are extremely fine metal powders that will absorb UV light when suspended in a solvent or water (trans oxides are most commonly used in automotive paint). Since truly transparent metal only exists in the Star Trek universe, no wood stain with UV protection is actually "clear;" all of these products have at least some tint of color because of the trans oxide powders, which are available in wood-friendly pigments of yellow, red, green, brown and black.

Except for the common trans oxide ingredients, there are wide variations in the formulas. Much is concealed as proprietary in the MSDS and technical data sheets, but common ingredients in many of these products include mineral spirits and xylene and/or another form of benzene. Sometimes the recipe includes surprises: a few have ethylene glycol (antifreeze), and some have a fungicide banned in some countries.

A common way to evaluate these products is to compare the percentage of VOCs vs solids in the formula. California and many states in the Northeastern U.S. have limits on the total amount of Volatile Organic Compounds that can be included in paints and stains, and all of these products are compliant. Asking knowledgeable professionals (roofers, senior paint store salespeople, shingle and wood stain company reps) about this issue, I found confusion abounds. Workers in the trade assume high VOC numbers are signs of a better product, and more than once it was suggested that better stuff is available out of state -- a claim that approached urban legend status because no one could name what product and what state had the goodies. Contradictory, I was also told by some that low VOC numbers are a measure of quality -- that the chemicals are rip-off fillers that evaporate quickly. In truth, I don't think any generalizations can be made that low/high VOCs are a way to judge quality, but percentages (usually in grams per liter, or "g/liter") are given with some products below.

To compare the different products, I set up an experiment: four shingles (Maibec grade A Natucket) were each treated with a product that might be suitable for reshingling. On July 4, 2008, the shingles were nailed to a board, which in turn was mounted on the southern face of the house. To accelerate aging, I spray the shingles with chlorinated tap water 10-12 times a day. The experiment will have limited value to this project because our decision will have to be made in a few weeks; I intend to continue the test until 2010 or so, however, and post updates here.

Pictured below are the four treated shingles; in the lower part of the image is a closeup showing the wood after it was hit with a spritz of water.


1 Flood's CWF-UV Shown here in their "clear" finish, Flood's UV formula is not being considered for this project because it's not recommended for use on new wood. The company's website states that new wood should be instead saturated with their water-soluble "New Wood Defender" for a year, but oops -- that turns out to be a discontinued product. Their telephone customer support rep says they now suggest that new wood just be left untreated until it's dry enough to absorb a drop of water in twenty seconds. This product has an unusual oil/water formula with about 60% VOCs, most of it paraffin/naphta. Flood is the only company here that offers a warranty on UV damage (4 year).


2 Weather-Bos™ Shown here is three coats of their Roof Boss "Formula 5." With its water-based formula, this is the greenest product on the market. Because it's so safe, the company doesn't have to reveal much about the formula (it says only that the product contains "natural oils and resins"), but their stats are far better than the competition: "up to" 72 percent solids, and a tiny amount of volatiles -- just 120 g/liter. Weather-Bos™ offers no warranty (except for defective products) but does offer an interesting rant on the meaninglessness of "guarantees."


3 Cabot Clear Solution Shown here in their 9200 series "natural" formula. Cabot's has an excellent reputation, and white cedar shingle distributors Maibec and WCS offer shingles pre-treated with the product. A linseed oil-based formula that the company suggests be re-applied every 2-4 years, it has 250 g/liter VOCs and is 64 percent solids. Warranty: replacement cans or refund if defective.


4 TWP (Total Wood Protectant) Shown here is the formula 515 "Light Cedar." Its heavy paraffin oil content results in far more water bead than any other product, as seen in the photo detail above. This particular recipe is 60 percent solids and 350 g/liter VOCs. TWP also contains Folpet, a broad-spectrum fungicide that is highly toxic to fish and invertebrates. But kudos to the company for alerting consumers to this risk; Cabot Clear also contains Folpet, but doesn't mention its toxicity.

There are many other wood preservatives on the market that might be appropriate for these shingles. Another TWP formula is less widely used, but may indeed be the best solution for our project; information on that will be included in the update to appear below. Here are three other candidates that aren't included in the test:

Sikkens Cetol SRD A popular Canadian finish that contains over 60 percent volatiles (mostly mineral spirits) and about 38 percent solids. The U.S. shingle mill WCS offers wood pre-treated with Sikkens.


Penofin Based on the exotic ingredient of Brazilian Rosewood Oil, Penofin also includes a familiar mix of benzines and paraffin/naphta. Performance is about the same as other products; reapplication every 2-4 years is recommended, and as often as every 9 months on horizontal surfaces.


Olympic Semi-Transparent Premium Acrylic Stain This latex coating is a possible contender because a leading Candadian white shingle mill, Waska, offers a 15-year basic warranty (fading NOT included) when two coats of the product is applied at the factory.

Of all these products, Weather-Bos™ is by far the most obscure; I've yet to meet anyone else in California who knows about it. Candice had used it at her home in Portland, and I later tried it on a redwood deck and cedar fence at our Sebastopol house. Weather-Bos™ certainly has the best stat sheet, winning both as the most environmentally safe and also having the highest levels of solids. So why doesn't everyone use their product? Partly because of the application issues: They recommend a minimum of three coats, but for optimum performance you should apply as much of the stuff as the wood will absorb. For maintenance, users are advised to "power wash it once every year or so" and apply another light coat. They also suggest washing your precious wood at a pressure setting of an incredibly high 3,000 PSI (don't stand in front of THAT fire hose).

This is a product that I'd like to give an unqualified endorsement, but can't. That earlier cedar fence was treated with over three coats (I recall it was at least five, maybe six), and was beautiful for a couple of years. But now five years later, there's little color left. I'm certain that a power wash followed by applying an oxalic acid cleaner and another coat would do wonders, but I can't do that level of maintenance every three years on a house of this size. I would probably try it again on another fence or similar project, however.

A June, 2000 Consumer Reports survey on lightly-tinted deck treatments ranked TWP, Sikkens, and Penofin as the top 1, 2, and 3 (respectively) products. Sold locally by Kelly-Moore Paints, TWP was also anecdotally recommended more than any other product, and I couldn't even find anyone complaining about the stuff in online discussion forums, which is a remarkable tribute in itself. The best testimonial, however, comes from the product in its worst shape.

It seems odd that a paint store would have a shabby look, but that's the case of the Kelly-Moore store in Novato; its rough cedar siding was last treated with TWP nearly eleven years ago, in the autumn of 1997. The photo at right shows the south face, which has endured the most weathering. The original color is intact wherever the wood grain is raised; the rest has aged to gray. The color hasn't turned black, which is an often-heard fear about these newer formulations, and the stain hasn't flaked off in patches. Most impressive of all, if the image is desaturated of color, (see inset) the overall brightness remains nearly uniform to its original levels. Yeah, viewed closely and on such long boards, the finish does appear mottled -- but on shingles with 4 ½ inch exposure, I believe the effect would be a graceful transition from the natural cedar to classic weathered gray. Or should we try to forever preserve the color of new wood?

An update appears in the post above.

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