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Linseed Oiled, now black mildew- Help

Discussion in 'Wood and Canvas' started by jennesspond, Sep 12, 2015.

  1. jennesspond

    jennesspond Curious about Wooden Canoes

    Hi All, I applied boiled linseed oil thinned with mineral spirits, to the inside and outside of my '42 Old Town after stripping, sanding, and repairing. It looked great after I applied it but a week later, black mildew is forming!!!! What should I do next to get rid of the mildew, before varnishing. Thanks for the help, Ken.
  2. Dan Lindberg

    Dan Lindberg Ex Wood Hoarder

    No responses yet.

    I'd re-bleach and re-clean. I use tung oil on the inside to avoid this. Also, I mix in the mildewside (sp) packets sold at the box stores to get a little "bug poison" in the mix. (I include it in the filler also.)

  3. OP

    jennesspond Curious about Wooden Canoes

    Thanks Dan, by re-clean you mean with TSP? or should I try to get rid of the linseed oil by using mineral spirits?
  4. Larry Meyer

    Larry Meyer Wooden Canoes are in the Blood

    While using linseed oil is often recommended for many purposes, I have come to hate the stuff. On whatever I have used it, it soon developed into a dark, hard to remove mess.
  5. Dave Osborn

    Dave Osborn LIFE MEMBER

    I occasionally get Kevlar canoes in the shop that need new gunwales. I have a Bell in now that had rotted gunwales.
    They were coated with linseed oil and are very dark and gummy. I will be reusing the thwarts, and decks which were also oiled. Tried sanding the deck and immediately loaded up the sandpaper.
    Any ideas what to clean them with so that I can sand them prior to varnishing.
  6. Todd Bradshaw

    Todd Bradshaw Sailmaker

    I'd probably try a light coat of stripper. Personally, I find linseed oil to be terribly over-rated and I'd go with bare wood on my boats before I'd put linseed on them. When you can get products like Deks Olje #1 that don't get gummy, don't turn black, dry within about a day, seal and develop a decent finish much faster than linseed and are so easy to renew on exposed surfaces it's hard to make any logical case for using linseed oil. Watco is another good one, but doesn't build and dry as fast. The tests from the Forest Products Lab also showed linseed to be perfect rot food. Aside from possibly silicone, it holds the distinction of being at the top of my list of "boat products" that should never get near a boat.
  7. Sudsmixer

    Sudsmixer Curious about Wooden Canoes

    As a chemist that develops cleaning products let me talk about linseed oil for a minute. Linseed is basically flax seed oil. It is composed of fatty acids like linoleic and oleic acids. This means you can eat it, like any other vegetable oil. It is nutritional for humans, animals and of course mold.

    Where Linseed oil is different than say canola oil is its ability to polymerize. Contrary to what people think, linseed oil does not evaporate or loose any of the oil as it "dries" The molecules undergo polymerization where many small molecules join together to make very large ones. This changes the material form a liquid to a semi-solid. The polymerization degree will vary greatly depending on the quality and age of the oil and what additives are in the oil (catalysts).

    Now to the mold problem: When you have "dried" linseed oil in a dry environment, mold is not able to "eat" the oil because of the molecular form of the oil. But, when you keep it wet for an extended period of time, and especially if it is warm and dark, the oil will start to break down and some of it will get rancid (oxidized) just like you can get rancid butter. This is perfect mold food. So under canvas equals wet, warm, dark and add a source of mold food and you have the best possible place to grow mold.

    How to get rid of the mold? Well, unfortunately, the linseed penetrates far into wood. You can bleach the color of the mold away using say chlorine bleach, but the mold is already established inside the wood where nothing can get to it. If it gets wet again, the mold will return. As far as I know there is no know way to permanently remove mold from a porous surface. You could try to get as much of the linseed oil off as possible, using say mineral spirits or another solvent, but I doubt you could ever get it all out of the wood.

    On anti-mold compounds. I have not researched what is available to consumers. However, they are used extensively in various professional formulas. The compounds that are affective against mold are also extremely toxic to humans. I'm not afraid of chemicals and I suit up, wear gloves and work in a fume hood if possible when using them. Be careful with any anti-mold compounds.

    In conclusion, I would never put linseed oil on anything that will ever get wet for any length of time, especially a canoe.

    edited for clarity.
    Last edited: Sep 14, 2015
  8. Larry Meyer

    Larry Meyer Wooden Canoes are in the Blood

    I'm not 100% sure but I may have linseed oiled the first canoe I ever restored and canvassed. And that likely caused the premature demise of the canvas - mold rot.
  9. OP

    jennesspond Curious about Wooden Canoes

    Wow, wish I had asked before applying it!!! I guess I will try all the above to get rid of it. Thinner, stripper, tsp bath, then mildewcide and see what happens.
  10. Larry Meyer

    Larry Meyer Wooden Canoes are in the Blood

    If your canvas is treated with mildewcide, that should be a help. Cedar is very rot resistant. I suspect the hazard is that the “liner” of decaying linseed oil infects the canvas.

    If you’re going to put anything on the unvarnished side of the hull, I suspect shellac would be a better choice? What say you to shellac, Sudsmixer?
  11. Sudsmixer

    Sudsmixer Curious about Wooden Canoes

    My expertise is cleaning stuff off, not so much putting it on in most cases. Knowing what shellac is, I would think it would be fine. Currently I am considering diluted spar varnish on my restoration when I get to that point. I am researching the chemistries now, I will post more if I get more useful information. I would like to hear others opinions on the matter too, please :)
  12. woodfyr

    woodfyr Restorer

    Epifanes Rapid Coat is an excellent product for interiors. Seals and protects and has a nice finish.
  13. OP

    jennesspond Curious about Wooden Canoes

    Cleaned with mildew killer, then re-oiled with tung oil mixed with mildewcide and mineral spirits. 2 coats varnish, starting to look good. WP_20150920_17_45_55_Pro (2).jpg

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