I recently finished White Oak Adirondack chairs with Watco Teak Oil. Now, a
week and a half later, the recipient says that black dots are appearing on
the wood. Sounds like mold to me. I switched to this finish because I read
that this could happen using linseed oil outdoors. The Teak Oil
descriptions 'sounded' perfect for this type application. I applied the oil
with the wood completely dry. Looks like I'll have to sand and start over
with something else.
Any suggestions here? Has anyone used Watco Teak Oil in this manner? Has
anyone had good luck with a particular exterior oil finish? Any help here
would be greatly appreciated!
I kinda agree re:marine varnish, but you'll still be scraping, sanding
and refinishing down the line. This is why boat owners cover their
boats, UV does a number on anything, given enough time.
How about oil stains, like they use on decking? Still lasts maybe two
years, depending on your weather conditions, but it doesn't form a
film, so when it starts to fade, you just clean the wood and add
another coat. Like maintaining a deck or fence when you prefer the
just-cut look of the wood, as opposed to silvered.
I am of the opinion that your black spots are from some form of iron
deposits, maybe from steel wool or rust dust ? Do not go for the
varnish option, have you tried scraping a thick coat of laquer to the
wood for recoating. I suggest Danish oil and rub some on every month or
so to build up some protection. 5 mins a month or days of scraping ?
White Oak lumber is a good choice for outdoor projects *** But *** it will
discolor from its original color as it weathers. White oak is a open pored
lumber and has a large amount of tannan in it. The grain of the wood will
start to turn black as soon as it is exposed to iron that is contained in
most water, including rainwater. The only way to prevent this is to
completely water proof the surface of the oak lumber. You will have to
recoat the lumber almost every year to keep moisture from getting beneath
your finish and discoloring the wood. Most varnishes, without constant
maintenance, will not tolerate constant, long exposure to the suns UV light
and still maintain a water proof surface. Spar varnish is a starting point
and a sutable finish if you are willling to recoat it from time to time(at
West Systems sells an epoxy system that is used a lot in boat building and
is designed to waterproof outdoor woods. I have had good luck with their
epoxy on white oak after several bad experiences with varnishes and
polyurethanes. Their epoxy uses a special hardner that turns the epoxy a
amber color that is similar to the color of wood that has had oil based
varnish applies to it when it is applied to white oak. The epoxy if left
uncoated will not stand up to the UV of the suns rays. So, you will have to
coat the epoxy with a UV blocking material after the white oak has been
water proofed with epoxy. White oak is one of the most difficult of the
woods to keep from showing black streaks in its grain structure because it
is so reactive over a period of time with trace amounts of iron that is
almost always in water. If any part of the finish on white oak developes a
hair line crack, a surface pore fails to be completely filled, or if the
finish is thin enough in a tiny spot to let water under it, then over a
short period of time that spot, crack, or pore that is subject of water
invasion will turn black/grey.
The above is true, epoxy needs UV protection; however, there is another
Epoxy and white oak are not very compatible.
It is the one place where epoxy is not a good choice for an adhesive.
SFWIW, resorcinol glue is the boat building standard for white oak,
epsecially for laminated parts like ribs.
Did you use steel wool on the oak? Iron combines with oak tannins to
make black stains when exposed to moisture. Any fasterners you use
on exteriors oak should be stainless steel for that reason. Also
if you wound up with red oak instead of white, it will mold and
rot easily. Can you blow air lengthwise through a small scrap?
If so, the wood is porous and it is red oak, not white.
Regarding the oil you use, are the ingredients listed on the
containers? Can you get a Material Safety Data Shet (MSDS)?
I'm, pretty sure that teak oil IS linseed oil. It is sold for use
on teak, not made FROM teak and will be basicly the same as any
other linseed oil finish, just linseed oil, a little solvent
like mineral spirits, and maybe a bit of colorant.
If you insist on an oil finish try Tung oil. NOT tung oil FINISH,
which again may be primarily linseed oil.
Oil _FINISHES_ are usually linseed oil, regardless of what adjectives
are used for them. Read the label. 100% tung oil will be better than
linseed oil, but as others have noted oil is not a very good finish
for outdoor applications. Neither are 'water seals' which are
usually waxes and will rapidly degrade and/or sublimate in direct
sunlight. For outdoor use, depending on climate an oil finish
would typically need to be reapplied once a year or so, a
water seal every four to six months.
For example, Formby's Tung Oil Finish is a blend of tung and other
(e.g. linseed) oils and resins. Basicly it is long-oil wiping
Penofin oil finishes are supposed to be made from oil from Brazilian
Rosewood nuts or something like that. But always check the label to
see what it is that they are really selling.
Thanks to all that replied. I believe, after talking futher with the
recipient of the chairs, that the problem was caused by steel wool. I
thought I got all of the steel dust off, but apparently not. That makes
much more sense than mold.
Any suggestions for removing these little pesky reminders of my mistake?
I preffer using oil to film finished because of past problems with
moisture getting under the finish. With oil, the owner of the chair can
decide to recoat every year (easier with oil) if they want, or just
letting it naturally age. This Penofin oil sounds pretty interesting.
I think I'll try that next.
Now, onto getting rid of the spots on Spotted White Oak Adirondack
Go to a Marine supply store and get some Bronze wool. This is what they use
on boats to eliminate the problem of rusting steel wool fibers. Use this to
remove the old oil finish with mineral spirits or acetone as a solvent.
Then use extra fine Bronze wool to reapply the oil finish of your choice.
You will need several coats of oil and annual maintenance will be required.
I used to have a boat with a lot of teak. Now I know why boat manufacturers
now use stainless instead of teak wherever they can.
Go to a marine store and get yourself some 2-part teak cleaner.
Regardless of the wood you use it on, it should help you out. It's a
acidic cleaner and a neutralizer.
Incidentally, I _used_ to be heavily into boating, had a
sportfisherman with a teak cockpit and cover boards that were
oiled/sealed. If I didn't strip the sealer off on a regular basis,
the teak would start turning streaky black underneath, and also show
spots. In all those years of killing myself with teak (and it does
look beautiful when done properly) I always wondered if it was a mold
spore that grew in the grain because I never, ever used steel anything
on that teak. Of course... a lot of fish blood was let in those
cockpits <grin> and maybe it had something to do with it. But the
coverboards were at least 24" higher than the cockpit, and most of the
bigger (100# and up) fish came in thru the transom door.
Incidentally, don't overdo the teak cleaner because acid treatment
will soften the "bung" of the wood and you'll wind up with very uneven
Part "A" is phosphoric acid.
Part "B" is caustic soda.
BTW, dilute phosphoric is sold as muriatic acid for swimming pool use.
Anyway, the phosphoric eats away at the soft pulp of the teak, then the
caustic neutralizes the phosphoric as well as removing any coatings.
After all, caustic is basically paint remover.
You then get to wash down the teak with fresh water, let dry, then sand
down all the ridges left when the soft fibers were eaten away by the
phosphoric, so that it will be smooth and you can start the whole
process over by laying varnish.
Couple of years of that and the bungs covering the screws holding the
teak start popping out.
Couple of more years and it's time for a replacement teak job.
The above is something I would consider completely inappropriate for
The hour was late and I had a brain fart. I stand corrected.
Having said that, neither phosphoric nor hydrochloric are things you
want to play with on any kind of regular basis.
Unless you work in a Pepsi Cola plant.
Not exactly. Dilute phosphoric acid, with some other additives, is sold
as Pepsi Cola, Coca Cola, and numerous other "Cola" flavor soft drinks.
(one summer in college, I had a job in a plant that made beverage syrups
for fountain soft-drink machines.
Note: the phosphoric acid content is what made Pepsi, etc. good for cleaning
the corrosion of battery terminals, and/or bugs off windshields.
Muriatic acid is also commonly known as hydrochloric acid.
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