This follows the threads "recipe to restore VOCs?" and "more on paint/
stain VOCs." It's my experiment on "doctoring" deck stain to get
better performance. This is Episode 1.

I bought a pint of Klean-Strip boiled linseed oil (BLO) and a gallon
of Klean-Strip 100% mineral spirits paint thinner, and intend to use
them to modify my new reformulated retail oil-based semi-transparent
deck stain in the hope of improving its durability and water
resistance. Because I'm adding linseed oil, I'll also add some
mildewcide.

The BLO says ZERO VOCs on the label and in its MSDS (online), which
presumably means no solvents added. There is no info on the label or
in its MSDS about ANY additives, like metal salts, and the MSDS lists
no concerns of carcinogens. (Other manufacturers' MSDS sheets list
things like cobalt as a hazard...) I HOPE there's something added to
speed up drying... It's somewhat thicker and more yellow than cooking
corn oil.

If VOCs were the only concern, it would appear that anyone, anywhere,
is perfectly free to add as much zero-VOC BLO as they like to any oil-
based stain or paint, assuming chemical compatibility, without
violating ANY VOC regs. But there's more.

I assume that there are good reasons to add a solvent as well as the
BLO to my deck stain, since just about every recipe I've seen for
other applications uses both. Maybe it improves penetration. I assume
that lower VOCs were obtained primarily by reducing or replacing the
old solvents in paints and stains, which may account for the poor
performance. So I figure I'll restore 'em.

The mineral spirits label says 791 g/l VOCs, while its MSDS says 815 g/
l VOCs. I don't quite know how to reconcile this; maybe I got an old
one... The MSDS bulk density of this product is 6.380 lb/gal.
Multiplying that by 120 gets 765.6 g/l, which is LESS than either
listed VOC content! I can't resolve that one, either. (That conversion
factor should really be 119.83, but everyone uses 120...) Any way you
do it, though, it's 100% VOCs.

The questions remain: how much shall I add, and in what proportions,
to a gallon? And can I do it without violating the VOC regs? (I really
don't care about the latter, but I'll play the game...)

I have several cans of stains, some new and some old. The VOC numbers
range from 250 to 610 g/l. I will assume that it will be perfectly
legal to add stuff as long as I don't exceed the original VOC number
on any given can. So how do I do that? Easy. All I have to do is mix
the BLO and mineral spirits separately in a proportion that produces a
mix with a net VOC content less than or equal to that number. Then, no
matter how much of it I add to the stain, the original VOC density
will not be exceeded.

Let's say the stain label says 350 g/l VOC. I have BLO at 0.0 g/l VOC
and mineral spirits (MS) at 791 g/l VOC. Let f be the fraction of BLO,
and (1-f) the fraction of MS. The proportions to match this number are
found from:

350 = f * 0.0 + (1 - f) * 791

which reduces to f = 0.558 BLO, (1 - f) = 0.442 MS. Since the MS is
the VOC source, that 0.442 is the MAXIMUM fraction of MS allowed. So I
could use anywhere between 0.0% and 44.2% MS, with 55.8% to 100% BLO,
as long as the sum was 100%. To make things simple, I'd probably go to
a 40% - 60% mix, or 2 parts MS to 3 parts BLO, as the max.

If that number were 100 g/l VOC, as has apparently become the limit in
southern California, the result would be only 12.6% MS as the max,
with 87.4% BLO, or a ratio of 1 part MS to 7 parts BLO.

So now I have a guideline for satisfying the VOC regs. The next
questions a Is the mix compatible with the new formulations? Do I
want the MAX MS mix, or something less? And then, how much of the mix
shall I add to a gallon of stain? More to come.