Beautiful mahogany decking.
Beautiful mahogany decking. Beautiful mahogany decking.

Have you noticed any differences in the stains you use on your mahogany decks? Several years ago, Cabot’s Australian Timber Oil (ATO) stains looked like…well…stain: Dark and oily. You mixed up a can up and solids would rise and lighten the oil somewhat. You brushed it on your wood decking and instantly, the mahogany took on a deep, rich color. The stain soaked in, and after a few hours the decking was dry. Nice. But the new stuff….You open the can and wonder if it is mislabeled. While the stain is called “Mahogany Flame”, it has a light, milky color, nothing close to mahogany or anything flame-like. What is going on here?

On the left, Cabot's oil-based ATO stain. On the right, their reformulated stain doesn't look the same in the can, even though it is the same color after application.
On the left, Cabot's oil-based ATO stain. On the right, their reformulated stain doesn't look the same in the can, even though it is the same color after application. On the left, Cabot's oil-based ATO stain. On the right, their reformulated stain doesn't look the same in the can, even though it is the same color after application.

VOCs and the Law. Volatile Organic Compounds, or VOCs, are the gasses that stains, solvents, and other products emit that react photochemically with the atmosphere. Scientists know them as isocyanates, while normal people just think “pollution”. VOC regulation grew out of concerns about air quality in urban areas (smog), about the wide variety of related health issues, and about depletion of ozone in our atmosphere.

The first regulation of VOCs began in California in the 1970s in response to the smog problems in Los Angeles. The two primary organizations that establish VOC limits in paints and coatings are California’s South Coast Air Quality Management District (SCAQMD) and the Ozone Transport Commission (OTC), formed by a coalition of northeastern states (Virginia, Maryland, Delaware, New Jersey, Pennsylvania, New York, Connecticut, Rhode Island, Massachusetts, Vermont, New Hampshire, Maine, and the District of Columbia) and recognized by the Clean Air Act Amendments of 1990. Nationally, the EPA plays a role as well, but the strongest regulations originate at the state level. Paint and stain companies have had to reformulate their products to meet lower VOC limits established by the SCAQMD, OTC, and the EPA.

Water and Oil DO mix. In 2007, Cabot reduced the mineral spirits and increased the oil in their original series 3400 ATO. This was the series 9400 ATO that was met with some decidedly mediocre reviews. In 2012, Cabot further reformulated ATO and introduced their new series, 19400, which I’ve had a chance to try out. This preservative stain uses water, rather than mineral spirits, to transport the oil to the wood. I know, you thought oil and water do not mix. So did I, but this is “water miscible” oil where the oil and water mix together at the molecular level (like mayonnaise). So you brush the combination into the wood and the water evaporates, leaving the oil to protect the wood fibers.

I compared the new “water based” series 19400 ATO (with the blue cover) to the original “oil based” series 3400, with surprising results. After three months, I found that mahogany boards stained with the new ATO were noticeably darker than boards stained with the old 3400 series ATO.

The stain test after 3 months.
The stain test after 3 months. The stain test after 3 months.

At six months, the difference was even more apparent: the water-based ATO holds its color better than the old oil-based ATOs, especially for the darker shades.

The stain test after 6 months.
The stain test after 6 months. The stain test after 6 months.

Applying the new water-based 19400 series is a little trickier than the older oil-based standard (you can find my tips for applying stains to mahogany decking on my website). For one thing, I found that the new stain takes longer to penetrate mahogany than 3400- and 9400- series ATO, and if there’s any excess, you need to wipe it off within a few minutes. It also takes much longer to dry – like 8 hours or more vs. a couple of hours for the older, higher-VOC products. But the results are worth the wait.

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