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!
Agree - Teak oil is what keeps sailors busy with their religious wood finishing all of the time. We oiled the wood on our boat every year until we got smart and used spar varnish.
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 least yearly).
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.
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 varnish.
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 chairs....
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 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.
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 white oak.
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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