Construction forum - Shellac info (Re: Vapor barrier coating for particle board)

Author

Shellac info (Re: Vapor barrier coating for particle board)

Ron Hock

2007-07-31, 1:25 pm

Mail Man Bob wrote:
> Thanks everyone for all the great info. I'll trot down to the shellac
> store and let you know how it turns out.

Mix it yourself, Bob. The pre-mixed stuff comes with the risk of it
being too old to work properly. Once mixed, shellac and alcohol begin to
form esters that retard drying and reduce the dried film's water
resistance. Use denatured alcohol (again, buy fresh as it absorbs water
from the air while open and most half-cans that are sitting around
probably contain more water than you'd want) in a ratio of about one
pound shellac flakes to one gallon of alcohol (precision not required).
For smaller quantities, do the math.

It's my opinion that the reason shellac fell from favor a few decades
ago was due to the prevalence of canned shellac that didn't perform as
well as it could because it was too old. That, and the hoopla around
those new polyurethanes led the market to assume that shellac was
old-hat. There's still a prevalent myth that a wet glass will leave a
ring on a shellac finish but that's not true if the shellac had been
freshly mixed. Shellac will, however, soften in the prolonged presence
of distilled spirits (whiskey, et al -- so mop up after that party) and
it begins to soften at about 140F so you can't set a cuppa on it without
a coaster or it will deboss a mug-shaped ring.

Sorry to go on and on but the more I learn about shellac the more I like
the stuff. Good luck with your project, Bob. I think sealing those
panels is a good, healthy idea and I've no doubt that shellac is the
best finish to use.

Ron
--
Ron Hock
HOCK TOOLS www.hocktools.com & www.hockfinishes.com

Mail Man Bob

2007-08-07, 3:25 am

Where's a good place to get shellac for mixing yourself? All I could find
were quarts at Home Depot, but I'm sure they are pre-mixed.

"Ron Hock" <nospam@www.hocktools.com> wrote in message
news:7aWdnQjYD-QN-zLbnZ2dnUVZ_g-dnZ2d@comcast.com...
> Mail Man Bob wrote:
>
> Mix it yourself, Bob. The pre-mixed stuff comes with the risk of it
> being too old to work properly. Once mixed, shellac and alcohol begin to
> form esters that retard drying and reduce the dried film's water
> resistance. Use denatured alcohol (again, buy fresh as it absorbs water
> from the air while open and most half-cans that are sitting around
> probably contain more water than you'd want) in a ratio of about one
> pound shellac flakes to one gallon of alcohol (precision not required).
> For smaller quantities, do the math.
>
> It's my opinion that the reason shellac fell from favor a few decades
> ago was due to the prevalence of canned shellac that didn't perform as
> well as it could because it was too old. That, and the hoopla around
> those new polyurethanes led the market to assume that shellac was
> old-hat. There's still a prevalent myth that a wet glass will leave a
> ring on a shellac finish but that's not true if the shellac had been
> freshly mixed. Shellac will, however, soften in the prolonged presence
> of distilled spirits (whiskey, et al -- so mop up after that party) and
> it begins to soften at about 140F so you can't set a cuppa on it without
> a coaster or it will deboss a mug-shaped ring.
>
> Sorry to go on and on but the more I learn about shellac the more I like
> the stuff. Good luck with your project, Bob. I think sealing those
> panels is a good, healthy idea and I've no doubt that shellac is the
> best finish to use.
>
> Ron
> --
> Ron Hock
> HOCK TOOLS www.hocktools.com & www.hockfinishes.com

B A R R Y

2007-08-07, 9:25 am

Mail Man Bob wrote:
> Where's a good place to get shellac for mixing yourself? All I could find
> were quarts at Home Depot, but I'm sure they are pre-mixed.

Woodcraft, Homestead Finishing, or other better woodworking finish
suppliers. It comes as dry flakes or buttons, which need to be chopped
up for faster dissolving.

Personally, I've been very happy with fresh Zinnser Seal Coat, available
at GOOD paint stores, but not necessarily the big home centers.

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