canoe wood trim oil

-- Last Updated: Oct-19-10 5:13 PM EST --

I have been using the Watco Exterior oil that comes in a green can for a few years now. Recently I did an annual maintenance where I sand and re oil the wood trim on the canoe. Went to several places and could not find the Watco Exterior oil and was told it was replaced by the Watco Teak oil. After a week the canoe trim started showing dark spots I thought it was mildew. I bleached scrubbed and re sanded but the dark stains do not come off.

I am wondering if this is a result of using the watco teak oil? What could be causing these dark stains/spots?

If you were storing a wood trim canoe outdoors in tropical environment, what oil if any would you use?

sorry I would varnish
I use boiled linseed oil for oiled cherry but the boat is not in the tropics. If you have ash gunwales the mildew just collects IMO.

Teak oil is a mildew feeder too from what I glean in this article

I’d be willing to bet
that the dark spots are rust stains. Did you work the trim with steel wool prior to applying the Watco Teak Oil? I recently had a discussion with a high end builder who ran into the same problem himself. He, I and a couple of others were brainstorming the problem before we had one of those DUHH moments.

He had used steel wool as an applicator for the oil, then turned the boat over on the ground that night. The dew reacted with microscopic bits of steel from the wool and by morning there were hundreds of black spots.

The moral is, don’t use steel wool on the gunnels. Use bronze wool or synthetic pads such as scotch brite instead.

Marc Ornstein

Dogpaddle Canoe Works

Custom Canoe Paddles and Woodstrip Canoes

No did not use steel wool.

– Last Updated: Oct-19-10 7:20 PM EST –

Did use a sanding block. Your post describes how it happened. Treated the wood trim and the next morning the spots appeared. Someone that I know who works with wood furniture also thought it could be iron coming up from wood. I'd never heard of this and after success using the exterior oil thought it had something to do with the watco teak oil.

Varnish: I've thought about it but that might create even more trouble down the line with the way I use/abuse my canoe.

By sanding block I assume
you mean one of those foam, abrasive blocks, impregnated with grit. If so, I wonder if the iron came from the block. If you still have it, try sanding a scrap of wood and then letting it sit in a damp place for a day or two. Maybe even wet the block and and see if it develops rust spots. I really doubt that the iron was already in the wood or the oil.

Marc Ornstein

Dogpaddle Canoe Works

Custom Canoe Paddles and Woodstrip Canoes

Don’t have the sanding block anymore.
Marc, what would you recommend to remove the dark spots? Should I use another type of oil since I can’t find the Watco Exterior in the green can anywhere.

What type of bleach did you use?
For those blue-black iron stains in woods with high levels of tannins, removing the finish before treating with oxalic acid usually works. Sometimes more than one application is necessary. If it is fungus staining, Clorox should work almost instantly. Any local boatyard should be able to recommend an oil finish that is suited to your environment. Most exterior/marine grade oils contain mildewcides and/or metallic driers that discourage fungus, but these generally have a limited life and need to be renewed regularly. Elevating your boat farther from the ground and somehow allowing increased movement of air while stored can help to discourage mould spore activation, too. You can also simply throw in the towel, take the easy way out and stain your rails dark, like I did.

I am very close

– Last Updated: Oct-20-10 6:26 PM EST –

to throwing in the towel or considering the varnish route. The boat sits on a stand about 36 inches up from patio deck. I used the standard household clorox bleach diluted, let it sit on the wood for a half hour later washed, rinsed it. When the wood dried I went to the sanding stage and spots do not go away.

Never, never, ever will I buy a boat with wood trim without the option of garage storage.

Don’t give up on wood trim
If the bleach did not remove the spots, they most certainly are mot mold/mildew.

There is a product called Iron Out. It is sold in most good hardware stores. It’s used to remove rust stains from plumbing fixtures, in houses that have high iron content in the water. I would try that 1st. Test a small area. It may take more than one application. The product comes as a powder that you can dilute with water or mix as a paste. Once finished, rinse the wood thoroughly with clear water and let dry. If Iron Out doesn’t work, you can try phosphoric acid, commonly sold in hardware stores as rust remover. I suspect one of the above options will remove the stains (if they are rust).

As for re-oiling. I use the Watco Teak oil all the time and have not had any problems with it.

Marc Ornstein

Dogpaddle Canoe Works

Custom Canoe Paddles and Woodstrip Canoes

Watco Exterior
It’s still made. It’s made by Rust-oleum. See:

Lowe’s only carried the Teak Oil but special ordered the Exterior for me.


Very good
I will order a quart, thanks!

Marc thank you.
I will look for these products and see if the stains come out. I do appreciate your expertise and advice.

Teak oil
has been used forever by the yachting crowd. Apparently it stands up well to harsh environments and saltwater. I have been using it, and the biggest difference between teak and Exterior appears to be the teak darkening the ash. I like it.


Wood bleach
Brief overview from a respected source:

The labels show that Watco exterior is good on deck furniture etc. and that Watco teak oil is good for that and marine applications. So it would seem to me that the teak oil is better for our applications. Any chance you could post pics of the spots?


– Last Updated: Oct-21-10 7:23 PM EST –

Great link and information, thanks! I can already tell you that according to what I read it looks like I did not use the right bleach. The oxalic acid is what I will use and the instructions on stain removal are well expained. The process if done correctly would take an entire weekend. I'll wait until season is over next spring and do this right.

What about the Iron Out Marc suggested? Is this like the oxalic acid? Sounds simpler.

Once I take out the stains will consider varnish as Kim suggests.

Material Safety Data Specifications
No oxalic acid listed in the Iron Out MSDS:

If your black stains are caused by a chemical reaction between iron, water, and tannic acid in the wood, they are not rust.

Good paint stores carry oxalic acid or: