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Boiled Linseed Oil

Discussion in 'Tips and Tricks' started by Larry Westlake, Mar 29, 2012.

  1. Larry Westlake

    Larry Westlake Designer/Builder

    I think the following information will be of interest to beginners who intend to mix their own filler.

    In a search of the WCHA forums, the only thing I could find about double-boiled linseed oil was one filler recipe posted which specified it as an ingredient, and a brief discussion of that recipe.
    Several people reported that they used that recipe or a similar one. Mike Elliot of Kettle River Canoes used to have this same or a similar recipe posted on one of his web pages.

    Mike's recipe and the recipe in the thread mentioned above appear to be based on a recipe on the WCHA "Fillers" legacy web page, with the important difference that the "Fillers" page recipe does not specify "double-boiled" but only "boiled" linseed oil.
    NOTE the caveat on the WCHA page about differences between historical and current materials (and I would add, how they are labelled and named): it is critical for beginners/amateurs mixing their own filler to know that most so-called "boiled linseed oil" in the 21st century is actually almost the same as raw linseed oil, and has not been boiled or anything like it. In all cases that I tested, the modern product of that name lacks the qualities required for canoe-canvassing, and is totally unlike the "boiled linseed oil" of yesteryear. I tested 5 different brands and none of them were what the words indicated they were.
    As we learned from Watergate, "People don't lie anymore, they just change the meanings of the words."

    Double-boiled linseed oil, as specified by Mike Elliot and by the thread recipe (but unfortunately not by any of the "Fillers" page recipes), is what you must use for canoe canvassing. And just in case someone unilaterally changes the meaning of "double-boiled" on us, here is the test for the necessary quality: Just brush an even coat of the oil on to a piece of cedar and let it dry for a few days. If it is not tough-dry and non-tacky to touch after 2 to 3 days at 65 to 70 degrees F, its not what you want for filler. Make sure it hasn't just soaked into the wood so much that it seems dry (which uncured oil can do) but has actually dried to a surface film.
    Raw linseed oil and fake boiled oil will take approximately forever to dry. One test I did on #10 canvas took 5 months to dry through (tested by cutting) even though hung so exposed to air on both sides, and heavily doped with Japan drier.

    Failure of the oil in the filler to cure seems to be one of the causes of the dreaded "Blisters". Search the forums for "blisters" for an enlightening wealth of woe on that subject.

    Larry Westlake
    Last edited: Mar 29, 2012
  2. H.E. Pennypacker

    H.E. Pennypacker LOVES Wooden Canoes

    I don't understand. "It is critical for beginners/amateurs mixing their own filler to know that most so-called "boiled linseed oil" in the 21st century is actually almost the same as raw linseed oil." In fact, they're very different, and further, "double boiled" isn't very different from boiled. Exposure to oxygen causes linseed oil to polymerize, and heat changes the chemistry of linseed oil which causes it to polymerize faster. Today, chemical additives provide the catalyst to speed drying time. Boiled linseed oil has the added catalyst, and "double-boiled" just has more catalyst. Raw linseed oil takes a long time to cure, boiled takes much less. I buy boiled linseed oil from a variety of stores and it always cures to the touch within 2-3 days.

    I don't recall anything ever posted here that proves that "failure of oil" in filler is the cause of blisters. Whatever the truth is (this or something else), many people would like to know. I've never made my own filler, which may explain my success!
  3. Gil Cramer

    Gil Cramer The wooden canoe Shop, Inc.

    Blisters are caused by water on the inside of a canoe travelling through the planking gaps and washing uncured varnish solvents into the canvas. That's why the blisters are all along the planking gaps and go away within a year or two once the solvents have cured.
  4. MGC

    MGC Scrapmaker

    I don't know. It sounds reasonable. I do agree that moisture is more likely to come from inside the canoe. The open side of the canvas does not have filler or paint to protect it. The outside has both.

    Not so sure about Morris has raised small blisters even 10 years after canvassing and filling. If I take it out for a two or three day trip, it will raise small bubbles.
    They go away after a few weeks out of the water.

    So.....I think it has less to do with solvents and more to do with water from the inside. I think you are spot on about that.
  5. Dan Miller

    Dan Miller cranky canoeist Staff Member

    Note that driers are included in all of the recipes previously published in Wooden Canoe and reprinted on the web site. Whether added when the BLO was made or when the filler is mixed, the effect is the same.

    Note also that the Old Town records show a fair number of canoes returned over the years for failed finishes. Some things never change...

    Whose bright idea was it to mix oil with water in the first place? Maybe this is all Gerrish's fault!
  6. Dylan Schoelzel

    Dylan Schoelzel born in a canoe

    Linseed oil is just about the worst finish in the world. It is not abrasion resistant, it attracts mold, it has no UV protection, and when it comes time to moisture it provides virtually no barrier for liquid water and is perhaps even worse with water vapor.

    If you look at the ingredients of most oil based filler recipes, linseed oil is the dominating component. That just doesn’t make sense to me; using a very large percentage of a component that lets water pass through it almost instantly in a mixture that is suppose to keep water out.

    Put a marine paint on top of that filler and you are just asking for trouble. As water gets in the inside of the canoe it migrates between the hull and the canvas. The filler isn’t going to stop the water from passing through it because of all the linseed. Once the water goes through the filler and hits that layer of exterior paint which is a good moisture barrier it has no where to go but form blisters.

    Blisters typically form around the planking seams between ribs because that is the most direct path the water has to get from the inside of the canoe to the outside. Path of least resistance.

    Ever been to the Assembly when it rains? Just about everyone runs around and flips their canoes up side down......................

    The biggest difference between today’s boiled linseed and yesterdays is the drying agent. Boiled linseed hasn’t really been boiled, it just means a drier has been added to speed up the curing process.

    Today metallic driers are commonly used. White lead use to be the drier added to linseed oil. The big difference as I understand it is that most metallic driers are top driers and lead is a through drier. A top drier dries the top of the finish and not necessarily the entire thickness of the finish. A through drier dries the entire thickness of the film and it does so evenly.

    It’s for this reason that I think Japan drier is an absolute no-no in any finish or filler. Not only can solvents get trapped beneath/within but too much drier can make a finish brittle and crack. Of course there are very high quality driers out there being used in high end paints that perform well. But who knows what junk is being sold to the public off the shelf.

    All those published fillers are great places to start (thinking) but their foundation was laid with slightly different products than what is available today. Enamel is different today and so is the linseed oil. Doesn’t one filler specify that if you don’t add white lead to the mixture than make up the difference with silica powder? Say what? That’s ridiculous. White lead and silica powder are two different animals. Substituting one for the other has no logic to it other than to make up for volume. You should not be adding something into your filler just too solely increase the volume.
  7. griffing

    griffing Curious about Wooden Canoes

    Hey guys ,I put a thread the other day about wanting to mix my own filler.I have white lead and I thought that linseed oil was one to be added.Can tongue oil be used instead? Also I went to Fiberglass Coating here in St Petersburg Fl. and they said that Fumed Silica would work better than 340 silica as it is ultra fine and using a very fine canvas would get a great looking finish.Insl-X coatings has an oil base paint with a high volium of solids which has supperior coverage in that I seem to want to try it. Grover
  8. OP
    Larry Westlake

    Larry Westlake Designer/Builder

    H.E, I see that several people have weighed in on this since I got your post.
    What you describe as the characteristics of linseed oil is what I expected, but not what I got.

    30 and 40 years ago, products I used that were sold as "boiled" linseed oil acted like they should. For a number of years I did not use any linseed oil products for anything. When I started using "boiled" linseed oil again in the late nineties, it behaved like raw linseed oil, and caused a lot of problems. One of the worst problems was a canoe that blistered.

    At first I assumed it was just a bad batch or low quality product, so I just bought some more from local paint, hardware, or building supply stores. All the batches also behaved like "raw", not "boiled" linseed oil - extremely reluctant to dry, even with liberal driers added. Other woodworkers had the same problems. One friend suggested "double boiled" oil, which I tested, and it had the qualities I expected. I can't see any difference between it and the "boiled" oil I used years ago.

    Up till that point, I had never really cared about the chemistry or the process for making these products, but with several quarts of bad oil on hand, and a blistered canoe that needed repair, I started researching.

    You wrote, "In fact, they're very different..."
    Several sources I found contradict this. They say that today, "boiled" oil is just raw oil with metallic driers added. At one time, "boiled" oil was heat treated, though not really boiled. I haven't found any description of what "double boiled" means in this context. I don't assume it means the same thing as that term means in my kitchen, for instance.

    You are correct that heat treated oil is "very different". The heat treatment has already polymerized some of the oil, and polymerization completes faster when exposed to air - but as stated above, linseed oil labelled as "boiled" is not necessarily heat treated. It may just have driers added, and in insufficient quantity to successfuly counterfeit the real thing.

    You also wrote, "..., and further, "double boiled" isn't very different from boiled."
    Perhaps it should not be. But the several products I tested with those two names consistently had significantly different physical properties.

    Another product is available called "polymerized" linseed oil. This may be the manufacturers finally dispensing with the inaccurate terms "boiled" and "double-boiled" etc. Some of the manufacturers helpfully describe their process in a general way: it has been heat treated, has driers added, and some also have other resins/oils added. The ones I tested (Mohawk & Lee Valley) dried almost overnight and cured almost as hard as varnish. I don't think they are really suitable for canoe canvas since not very flexible. Their attraction for furniture is that they are easy to apply by wiping, but more durable and faster building than less modified oils.

    Just to get a more complete understanding of this issue, I also recently took some of my junk fake "boiled" linseed oil and heated it to smoking hot for several hours. A change from greenish yellow to medium amber colour was the only visible result, but it dried tack-free in about 4-5 days, a big improvement. Eventually it was as hard as varnish.

    It's late tonight, and I will not be able to write again till late Monday.
    I can dig up my reference list later, but I think that two of the most pertinent sources were in the Wikipedia and Fine Woodworking Mag websites. Some of my information was from discussions with people at Mohawk.

    Once we've talked out the subject of what's in the oil cans, I look forward to discussing the blisters issue.

    Larry Westlake
  9. H.E. Pennypacker

    H.E. Pennypacker LOVES Wooden Canoes

    The following is not meant to promote or condemn the use of linseed oil. All products have pluses and minuses, so this is meant only to add some food for thought. Bottom line? Raw linseed oil does dry, but very slowly. “Boiled” today means the addition of chemical catalysts. “Double boiled” simply means more chemical catalysts. And multiple factors affect the drying process and the color of oil films. These include heat, light, chemicals in the environment (like ammonia), etc. And because boiled linseed oil from different manufacturers contains different ingredients, the specific product and the environmental conditions in which it is used both affect the process of polymerization (“drying”).

    First, what does “boiled” mean? Archer Daniels Midland (ADM) was formed from the merger of Archer-Daniels Linseed Company and Midland Linseed Products Company nearly 90 years ago. On their website, they say about linseed oil, boiled and double-boiled:

    “ADMs Raw Linseed Oil meets the requirements of ASTM specification D 234-61T and TT-L-215-A. Scientific boiled meets ASTM specification D 260-61T type 1 and Federal specifications TT-L-00190C. Scientific Double Boiled contains more drier than Scientific Boiled thus dries faster.”

    Chemistry of drying oils (including linseed oil which is a type of drying oil) is complicated, but not that complicated. Bottom line – raw linseed oil does “dry”, but slowly. “Drying” means that the molecules in it cross-link or polymerize. Oxygen promotes that polymerization through the formation of carbon-carbon bonds or carbon-oxygen-carbon bonds between the fatty acid tails of adjacent oil molecules. Heat, light, and other factors affect the process of polymerization, so no matter what type of linseed oil is being considered, the rate of polymerization is not constant across conditions. Heat was once used to “kick-start” the polymerization process, but the advent of chemical “driers” made it easier for manufacturers to make a product faster, cheaper and more safely. These “driers” (technically called siccatives) are oil-based salts of metals that speed up polymerization by promoting the chemical crosslinking reactions. Because the order of activity (highest to lowest) is:

    Co > Fe > Mn > Ce > Pb > Zr

    cobalt is used most often as a chemical catalyst today. Note that lead (Pb) is way down the list. However, as others sort-of pointed out, different metal-oil salts affect different “parts” of the oil film. Cobalt catalyses best near the surface, forming a film that slows oxygen entry, which then slows curing deeper in the film. Lead-based salts tend to promote polymerization throughout the finish at much the same rate, which means “drying” throughout, not just on the surface. Therefore, a common drier set once included cobalt (fast but better at the surface) and lead (slower but throughout). Because of health risks of lead, it has been eliminated, leaving cobalt the most common drier today. Linseed oil containing cobalt will dry throughout, but it dries fastest on the surface, which can lead to wrinkling, especially of thick films. To deal with this, some manufacturers add additional driers. One of these at least – zirconium - mimics the effect of lead and promotes more rapid drying throughout the film.

    Note that linseed oil varies among makers. Rocochem (Canada) uses cobalt and zirconium; E.E. Zimmerman (US) uses cobalt and manganese. Cargill’s product seems to use cobalt only.
  10. chris pearson

    chris pearson Michigan Canoe Nut Maybe we should just go back to birchbark.
  11. Gil Cramer

    Gil Cramer The wooden canoe Shop, Inc.

    I had a really good theory until you messed it up with facts. Gil
  12. Rob Stevens

    Rob Stevens Wooden Canoes are in the Blood

    Doh! What are you trying to do, increase competition for scarce resources?

    Coincidentally, I got a call today from a TV Producer for "Wild Canada" who wanted to pick my brain about Canadian birchbark canoe builders. We haven't connected yet, but I think I know what she wants to know. I'm gonna start painting the canoe trees camouflage. Do you think linseed oil would work for that?
    Last edited: Mar 30, 2012
  13. Rollin Thurlow

    Rollin Thurlow member since 1980

    Lets face it, traditional canvas filler formulas are all a shot in the dark.
    The paints and oils from yesteryear were made from stuff that may or may not be similar to what is used today. The formulas were developed by builders that were not chemist but just using what worked. Using today materials and guessing how to change it to match what we suppose was used yesterday, is still just guess work. Until the WCHA underwrites a research project that has some serious academic capabilities we are still just using stuff we don't really know all their chemical properties and then mixing it other stuff with more unknown properties. Some of us have mixed enough goop that appears to have satisfactory results that we promote what we have and then we make up theories on why it works.
    I've heated oil, boiled oil, set oil on fire , added drier and then more drier, use less oil, used more oil, removed all drier, use raw, boiled,and used motor oil and all my research points to one thing makes the most difference.
    Allowing the filler time to dry or cure makes the most difference in the production of paint blisters. The filler has to be cured all the way through the canvas and that takes much longer than most people are willing to wait. The filler surface dries fairly soon so it would seem reasonable that its ready to paint but that is really only the start of the time it needs to cure!
  14. OP
    Larry Westlake

    Larry Westlake Designer/Builder

    Almost everything we might use in a filler recipe today is different than those with same names from 1900. Even the solvents are different. Heck, most of this stuff is very different than it was 20 years ago, let alone 120 - big changes lately because of the environmental concerns.

    If guys in the 1880's backwoods could cook up something with their available materials that worked without really knowing what they were doing, SURELY we can cook up something with our available materials that works reliably. We probably already know more than they did, and we live in a flipping information-rich environment with the world at our typetty-clickey fingertips. More about that in a later post.

    It seems that the commercial filler products really are pretty reliable, as long as you let them dry - as Rollin says. If you can get the dad-gummed stuff to dry, what's in it probably isn't as critical as we think.

    Since I used the same recipe that always worked before, I blamed the only ingredient that was already noticeably misbehaving on other projects, and that was the linseed. I know it was the culprit in this case, but don't deny that other causes affected other people. I tested the available linseed products to be sure how they behaved, both unsuitable ones, and the suitable ones. The "double-boiled" oil dries roughly 3 to 4 times faster than the "boiled" (brands vary a bit). Of course, this is for brands available to me here in rural BC, Canada, most of which I think will be available across Canada. Things might be different elsewhere.

    I had the exquisite displeasure of seeing the blisters form. I was at the launch with the customer, and as the boat came out of the water after about an hour of larking about, I was startled to see a pronounced weave pattern in several places where there should have been (had been!) a nice smooth glossy finish. Between the pattern of the threads, small pinhead-sized beads (as if of fluid) were bulging under the paint film, forcing it off the filler. The condition progressed slowly. Under continued pressure, the fluid detached larger sections of topcoat so that the beads coalesced into blisters.

    Clearly, what was happening was that the cotton was shrinking on becoming wet (as is its wont) and wringing itself like a dishcloth, squeezing the uncured binder out of the weave. If the binder (paint/oil/drier/solvent) had cured, presumably it could have resisted the wringing. Also presumably if cured, it would have reduced the amount of water absorbed and so reduced the force of the shrinkage.

    The customer used the boat for the season, I fixed it in the fall. After about a month, no new blisters appeared. None of the blisters were located at seams.

    There was one detail about the problem canoe that was different from the others I'd done. At the customer's request, it had #10 (approx=14 oz.) instead of 10-oz canvas, since it would be beached where barnacles abounded. Drying time probably increases as the square of the difference in thickness, or some nasty ratio like that (so that 1.4x as thick takes 1.96x as long!). But, since this canoe dried for two months before being painted, and was well over three months before being launched, it should have been dry if the linseed had not retarded the cure.

    When this hit the fan, I had never heard of this happening to anyone I knew. I found all the answers I needed in old WCHA Forum posts to back up what I had concluded. Without that reassurance, I think I might not have had the confidence to just go ahead and repair. I worried that it would happen again if my analysis was wrong.

    What has been said in this thread is much what was said in previous threads about blistering, but I think the red herring elements have been elliminated by Rollin's clear sum-up statement.

    The canoe that blistered did so over two years ago. It took this long to test everything thoroughly enough to be absolutely sure - some of the tests took months to cure.

    Before I had all my test results to prove my conclusions, I started using a heater to ensure curing. With the heater inside, a blanket-wrapped canoe can be safely & economically kept at a steady 80 degrees F while slung out of the way in the rafters. Chemical cure rates also probably respond exponentially to increases in temperature, so I think the extra 10 degrees above room temp is significant. I may continue to use the heater now.

    After two months at 80F, if the #$@%^&*! thing isn't cured, perhaps you used olive oil by mistake.

    Larry Westlake
  15. Fitz

    Fitz Wooden Canoes are in the Blood


    My Field Observations:

    The only time I get blisters is about Day 3 of a trip in Maine, where the Rain, Mainely, Falls in the Canoe. The Mainely water soaks through the canvas and filler and lifts the paint. This also happens after showing off my Sailing Abilities (ask Andre) and dumping a few times thoroughly soaking the entire canoe. I have one canoe that is particularly prone to blisters. It was one of my early restorations and I think I was overzealous with the sanding and probably used way to fine a grit in search of a perfect finish. I only go as far as 220 grit now. You need some tooth. I have noticed less of an issue with blisters.
    Last edited: Apr 4, 2012
  16. griffing

    griffing Curious about Wooden Canoes

    Could this problem be solved by saturating the cavas with a thined portion of the filler?I plan on varnishing with a 50/50 solution the planks like you would fiberglass and than applying the canvas.Yes no? Could this make for a problem? I plan on using the old fashion filler. The existing canvas on mine appears to have the original filler soaking through and is adhearing to the planks quite well.
    The paint company that I deal with has and additive for mildicide that they use in a latex paint for Florida and thought that it would work real good. Also the linseed oil that everyone talks about can be a higher refind type used fo commercial application. Grover Griffin
  17. OP
    Larry Westlake

    Larry Westlake Designer/Builder

    Varnish prime

    Grover: Since even very carefully measured and mixed filler recipes occasionally give trouble, anything like extra thinning is just asking for more trouble. Trouble is very educational, but seldom enjoyable or profitable. It is prudent to treat the ratios in existing recipes as if they were moderately critical.
    As I understand canvassing, adhesion is to be avoided, and I have never seen it on any of the factory boats I have repaired. For the most part, those old boats show good oil-saturation through to the inner surface, but no bonding at all to the planks. This is a nice balance.

    Applying canvas to wet-varnished planking will probably result in bonding. As I said above, I believe this is undesirable. It certainly will be unwelcome when the next guy has to recanvas, and chunks of cedar come away with the cloth.
    Canvas-covered plank boats are not structurally like composite wood-FRP (fiber-reinforced plastic) boats. Wood-FRP construction unites the three components into a single structural entity. Wood plank-&-rib + canvas-filler overlay operates as two completely distinct structural/functional entities.

    Larry Westlake
  18. Easternrivers

    Easternrivers Traditionalist

    Man! All this unknown and uncertain discussion about filler and blisters has my head spinning!
    What to use -What to use??
    Mike Elliot also mentions using commercial lagging compound as filler...
    Personally I found a company that had a product that was specifically listed for waterproofing canvas....
    I wonder if that's not the way to go and avoid this boiled oil issue?
  19. Dan Miller

    Dan Miller cranky canoeist Staff Member

    I experimented with a product called Childer's CP-50A, which is a lagging compound for sealing canvas insulation around pipes. In Canada, Bakore is a similar product. It had all the theoretical qualities that would make it a good filler, including abrasion resistance, mildew-resistance, flexibility, water-based so dried fast etc. Worked great, until the first time the canoe got wet, then strange things happened.

    Now I use either one of the Old Town unleaded recipes or the Ekofill process.

    Of course, if you stick to all-wood canoes, none of this is an issue... :p
  20. Easternrivers

    Easternrivers Traditionalist

    Yup...Bakor was one mentioned along with the Childers CP-50A.
    Dang it all....I thought that would be the answer...
    so? what sort of things happend when it got wet?
    Old Town has unleaded filler? How do I get some of that????
    I expect to be making a trip into BAngor before July..Could pick it up on the way back I guess.

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