Linseed oil mixed into Cob/Earth Plaster mix?

topic posted Wed, March 15, 2006 - 1:46 AM by  §hån
Heard from one dependable source that mixing linseed oil into the cob mix and perhaps an earth plaster mix makes for an incredibly resilient exterior surface. Can anybody corroborate this?

It's true that this sorta defeats the glomming function of the clay, but in an earth plaster mix as final exterior coat on a cob surface, this seems like a sensible water-resisting approach. Anyone done any experimenting with this?

Many Thanks,
posted by:
SF Bay Area
  • "BOILED linseed oil" is what you want, not linseed oil.

    And you can mix it, though I would suggest painting it on too. If you warm up the oil first then it will soak into the wall better. Or heat up the surface instead of possible (radiant earthen floor). But be careful when heating and with your painting equipment because boiled linseed oil can spontaneously combust, so avoid open flames and crumpled up oily rags.

    You can also whip up some wheat paste and use that as a finishing coat as well. I've used boiled linseed oil on a floor (multiple coats) and used wheat paste on the walls (one coat). Both worked great.
    • Unsu...

      Re: Linseed oil mixed into Cob/Earth Plaster mix?

      Wed, March 15, 2006 - 11:20 PM
      I have used raw linseed oil on several projects and it is fine. I use about 1:1 raw linseed to beeswax, melted together in a crockp[ot, and mix it at about 1 cup per gallon of plaster. the plaster rations vary, typical ratios are 4:8:4:2:1 ; clay, sand, fiber (paper pulp is great, chopstraw is the norm), wheat paste, oil/beeswax mixture. it comes out nicely with a burnish, which is time consuming but beautiful and rugged and highly water resistant.

      boiled linseed contains chemical driers which are known to be VOC's.
      • I haven't heard about the VOCs in BLO, just the heavy metals. I know that it is prefered by some people and is known to dry faster. It works great IMHO, though I have no experience with raw linseed oil.

        Here is a good article on different natural paints:
        • Unsu...
          raw is harder to get, I ussually order it in bulk- 5 gal. a shot. the reason BLO dries faster is because of 'driers', but most specs say that the difference is only 12-18 hours., so BLo dires in 30-36hrs where raw dries in 40-48. Becasue it is labeled as "boiled linseed oil" and not for consumption, the driers do not have to be listed. thus industry can say "VOC free" because they are refering to only the linseed oil. it is the additive driers that are VOC's and can cause respiratory and eye irritation. A google search of companies providing raw lineseed oil in your area should help you find a local retailer. I order through a neighborhood tru-value.
          • A'ight, I did some quick research with the "The Hand-Scuplted House" book and here's what I come up with:

            Regarding sealing and hardening earthen floors; on page 253: "With a rag, brush, roller, or soft sponge, apply at least four coats of boiled linseed oil. It is important to use boiled, not raw, linseed oil." No explanation on why follows this statement.

            Regarding earth plasters; on page 267: "Robert Laporte of the Natural House Building Center" adds 1 percent linseed oil by volume to his earthen finish plaster."

            Regarding natural paints; on page 272: "Boiled linseed oil is a cheap and readily available oil that works well for paints, though it does yellow somewhat when dry."

            I get the impression that raw linseed oil works better used as a mix, but boiled linseed oil works better as an applied finishing coat. Which makes sense to me, because I did only use the BOL on an earthen floor and used wheat paste (which rocks) on the earthen plaster instead. I think the BOL is preferred on earthen floors because of how it absorbs into the floor and strenghtens it?
            • Unsu...
              that could be (mix vs. finish application)- ive never applied oil seperately AFTER I laid my plaster down. and regarding the 4:8:4:2:1, the R. Laporte 1% sparked my noggin and I got out my notes, its been a while...

              4:8:4:2:.25 (16:32:16:8:1) is an average mix. so thats about 1.15% linseed oil by volume.

              nothing I have encountered indicates that raw oil with wax dries any softer than BLO. I ve used raw and BLO on about 6 benches, 2 BLO and 4 raw, and theyve performed eqaully well.

              I think BLO is perfered becasue it is industry standard and som much easier to get than raw and additive free linseed oils.

              and yes, wheat paste is GREAT stuff.

              I would think raw LO also yellows when dry, though I ve never applied it without an earthen binder.
              • Re: Linseed oil mixed into Cob/Earth Plaster mix?

                Fri, March 17, 2006 - 12:01 AM
                Wonderful Folks - Thank You!
                What I have gathered so far:
                1) Raw linseed oil heated with bees wax is a friendlier recipe and perfoms just as well as the boiled linseed oil in an earthen plaster mix (save the added drying time).
                2) Our proportions are 4:8:4:2:.25 ideally using paper pulp and wheat paste.
                3) There seems to be agreement about the mix proportions and performance observations.

                This is very useful. I was planning on doing some test boards with different levels of oil content, but as I want to get a bench coated this spring am afraid that short -term testing will be insufficient. So right now, without further information, I will follow your good recommendations. However, for the sake of further refinement and as ya'll are red hot, I have one more question concerning the mechanics:

                It seems logical enough that when coating plaster with the boiled linseed oil one wants to achieve maximum saturation, filling as much void between particles as possible and thereby blocking water penetration. The wheatpaste's function, I understand, is to bind the other materials together, ideally surrounding the clay, sand and cellulose particles without excess. In a mix, ya'll are suggesting a proportion of only .25 parts raw linseed oil to 2 parts wheatpaste, which I presume is due to the fineness of the voids not filled by the wheatpaste. If this is correct, 1) has .25+/-parts really been observed or tested to be the saturation proportion of raw linseed oil? And, 2) When mixing in my oil and wax component, should I be looking for an ideal consistency which = full saturation?

                Under Tarps in Alameda,

                • Unsu...
                  1) I know that the physical character of the clay changes notably with the addition of the @1% oil. I dont know if huge amounts of testing have been done, but one of my benches holds water, if that helps. Its 3 years through PNW rains, and no eroision. its like a ceramic tub.

                  2)the paper pulp should be made by presoaking the paper and using a big mixing paddle until its got an almost slimy consistnency. I think any fiber would do tho- remembr that if you paper has water in it you will need less water to make the right plaster consistancy.
                  • This is the maximum depth. Additional responses will not be threaded.
                    2) and wheat paste has water in it as well! if you use strawfiber you will need to add slightly more water.
                    • Additional research, this time from "The Art of Natural Building"

                      Regarding Earthen Floors by Athena and Bill Steen; page 116-17: "Traditionally, the most successful sealants have included oils, animal urine, and blood. Boiled linseed oil is probably the most cost effective and widely available option today. ... To improve penetratino, a solvent will be neccessary for thinning the oil. The options include everything from common mineral spirits and turpentine to more expensive but environmnetally friendly citrus oils and odorless turpentine. Oils penetrate deeper when they are warmed (carefully) and when the surface of the floor is also warmed."

                      Regarding Tamped Road Base Floors by Frank Meyer; page 119: "The best sealer I have found is boiled linseed oil, thinned with turpentine and brushed on in several coats (the odor dissipates in a week or two). This is an all-natural, non-toxic floor that has relatively low embodied energy."

                      This is only hearsay, but I took a workshop in earthen floors with Michael Smith of Cob Cottage Company fame and he specifically recommended BLO over raw LO as a sealant. He did not say anything about cob, just earthen floors as that was what the subject was.

                      Again, I find no mention of specifcally using RLO. Or of any concerns about using BLO for any reason or context. I am aware that these are only regarding floors and paints, and not about as part of a cob mix, so it seems that BLO is the preferred ingredient for the 'authorities' on natural building methods. This leads me to believe that using BLO in earthen floors is preferred as well as earthen plasters; cob is still up in the air.

                      I am not saying that you are wrong about using raw linseed oil in mixing cob, and I realize that natural building is mainly an experimental field of building and that experimentation in mixtures is highly recommended, but I would greatly appreciate it if you had some kind of source to back up your claims against BLO if you are going to be assertive about it. I like this discussion and I would like to read more about what you are debating.
                      • Re: Linseed oil mixed into Cob/Earth Plaster mix?

                        Mon, March 20, 2006 - 10:27 PM
                        nice to see so many of my friends quoted here. we have for many years now used only raw linseed oil in our plasters and on our floors. we boil our own oil and buy it in 55 gallon drums. BLO has heavy metal drying agents, known as japan dryers. as has been said these are highly toxic though technically not clasified as a VOC. Both Michael and Ianto had a bad experience with raw oil un boiled and overapplied never hardening. if applied correctly and the excess removed as you go RLO can be an excelent hardening agent for earthen floors.

                        in conversations with Bill Steen, Frank Meyer's and others they have confirmed their inexperience with RLO due to access.

                        Michael Smith and his new community currently purchase RLO from my company Vital Systems.

                        hope this helps clarify,

          • Re: Linseed oil mixed into Cob/Earth Plaster mix?

            Mon, October 8, 2007 - 4:16 PM

            Any way you could turn me on to your supplier of linseed oil? I have looked for hours and I'm not finding a very good supply. $725 for a 55 gallon drum (more than I need right now), or $18 for one gallon. How much do you pay for the 5gal. and where do you get it?

            I know this post is ancient, just found it. Thanks!
  • Re: Linseed oil mixed into Cob/Earth Plaster mix?

    Mon, March 20, 2006 - 10:47 PM
    linseed oil is well know as a wood sealer and multiple coating of boiled linseed oil is a perfect for exterior or interior applications .
    in old days linseed oil mixes with lime has been used for water sealing adobe and stucco, plaster mixed with linseed oil is well know as an original mix used for Venetian plaster... what is the actual application you are anticipating to use it for?
    • Re: Linseed oil mixed into Cob/Earth Plaster mix?

      Wed, March 22, 2006 - 12:42 PM
      boiling linseed oil will help prevent the oil from going rancid once applied. this may not be a big deal on the exterior of a structure, but on the inside, you'll want to go with boiled, or "polymerized", to avoid the eventual stench.

      most VOC's are pretty toxic, but "VOC" doesn't necessarily relate to toxicity, just as "non-VOC" doesn't necessarily mean it's non-toxic. Tried and True makes a polymerized linseed oil that contains no solvents, driers, heavy metals or anything but linseed oil. They also have a linseed/beeswax product.

      beeswax is water-soluble, so maybe not the best for exterior or floor applications.
      • Unsu...
        volatile organic compound.

        this is generally considered any organic (meaning the compound contains carbon) chemical compound that evaporates at regular temp and pressure.

        oddly enough turpenols/turpenes (refined: turpentine) a natural product of pine trees, is volatile. volatile simple means it evaporates as per above. Many are harmful, several are carcinogenic and some are straight up deadly. this is because carbon based compounds are highly reactive in our biology. our bodies, and most biology, easily absorb carbon compounds, and if they arent the ones we need, they can take up space that should be used for bioprocess, or they outright toxify the system.

        BLO with driers contains VOC's, but they dont have to be listed as they are ADDED, and not the primary product for sale. And as for VOC's not being necessarily toxic, true. but I am not an organic chemist, and companies are known to lie to sale their goods, and where the EPA and OSHA are honest, they are often behind in the research needed.

        SO, why bother risking toxicity if you have something that works and is known to be safe? Penny Livingston Stark's prudence principal goes into effect for me at this point...

        I have seen great bees wax/LO floors, including Rob bolmans original tiles that he took to lane county some 12 years ago. I have also seen some poor examples where the application is TOO exposed to moisture. I work with Sukita Crimmel and Lydia Doleman in PDX a bit, and they do some nice floors with BW/LO finishes; I look forward to watching them age as weve just done a few at this point, some 4 or 5, and the oldest is @ 3 years old. the last was radiant heated, so thats very exciting.

        BW/LO It tends to muddle a bit if it stays consistantly wet or the ratio of BW/LO is too high (the life house memorial in portland is an example of a BW/LO 'wall' that has too much wax and too much rain exposure.) however, with no direct rain, and normal west coast humidty, it does fine- the bench on the sauna in my pics is outdoors but partially covered, and has no mottleing. i might not use it on bathroom floors, but otherwise I think its a go.

        tried and true sounds like a neat company! i'l check them out! thanks for the reference, I think the market for natty building products is going to boom in the next decade, just like organic foods have in the last.

        • interesting to note...

          In my metal work I often use a Linseed oil, beeswax and turpentine mixture to seal metal.
          we heat it as well.
          • Unsu...
            FYI - this (sometimes w/ higher quality solvents) is also a mixture for dammar varnish which can be a medium or a top coat for oil painting
            • Unsu...
              Also in regards to linseed oil used in oil painting vs. natural building applications - after reading the other posts -- not sure this is relevant but the quality of the dried product in i think crosses over. In oil painting there are similar distinctions for the use of boiled linseed oil vs. non-boiled...the driers (i think they are petrolium based) having everything to do with it. on/in an oil painting boiled linseed oil yellows/oxidizes heaver over time. Also it becomes more brittle, ie: less plastic. so i wonder if by using the non-boiled linseed oil in a correct mixture the surface stays more flexible (more concern for walls than floors since they probably flex more)

              Also, in terms of drying..when using the non-boiled linseed oil, if its not mixed properly it never dries and will simply stay oily or become sticky.

              Linseed oil is used also as a dispursant (sp.?) for pigments which then makes some "oil" paints. It binds the solids of the pigments together and then dries in place...the quality of the oil indicates heavily the quality of the painting. I've wondered about this tons in terms of how it would apply to clay paints. After all, the pigments are the same - ochers, iron, etc.

              other oils used but much more expensive: (heres a link)

              Also, when you are heating these materials, this is again similar to encaustic painting -- read "caustic"! use face mask for organic fumes in a well ventallated room or outside!
    • Wow - I am really amazed at the preponderance of really good information!
      The actual application for the finish is a cob bench: quite large and uncovered except for an anticipated trellis. Aesthetically, some of the folks involved, wanted to see an earthen plaster finish but are also concerned about durability. We observed that in Portland, City Repair has built a few cob benches finished with earth plaster that appear to have endured their exposure to the rains quite well. As we're in the Bay Area, the prospect of doing something similar here seemed reasonable as well. Well, we've been cautioned about exposed earth plaster on more than one occasion, so I'm trying to get an overview of the imperical landscape of the subject. The input on LO & BW mixed with an earthen plaster containing cellulose looks like a route worth investigating further. Is there a more dependable exterior earthen finish? And in what form and how often will maintenance need to be performed?
      • tom
        offline 0
        Hello all. this is myt first post. I have a background in woodworking and am new to the natural building area. Has anyone tried using Carnuba wax flakes mixed with oil? It is harder than beeswax, more water resistant and comes from the leaves of the Carnuba tree. Not to be confused with Carnuba paste wax which usually contains any number of terrible chemicles. Also, where can i find pure rlo. The stuff at the hardware store has the same warning lable as the blo. I would like to try boiling my own, from what i've read in woodworking sources, true boiled linseed oil maintains its color and clarity better than the stuff with metallic dryers.
  • Re: Linseed oil mixed into Cob/Earth Plaster mix?

    Sat, August 26, 2006 - 9:04 AM
    Hey All,
    I've been working with BLO/RLO for several years now as a a sealant for exterior plasters and floors. Here's some points of my experience.

    *Raw linseed oil takes 5-6 days to dry, BLO takes about a day. This means, when doing for coats, and maybe a fifth wax coat. the time difference is between 4 days and 20.

    * There are toxic VOC's in linseed oil of all types. Some people are farirly sensitive to linseed oil for this reason. Use a respirator with organic filters for any larger floor. Exact VOC content and PEL's (permisssable exposure limits) can be found in many wood refinishing books.

    *The driers do not release VOC's. They are heavy metals, more specifically cobalt, zirconium and there's a third that I;'m blanking on now. Cobalt's the nasty one. These are toxic by ingestion and through skin contact. They are carried by the oil into the skin, and end up staying there. Cumulative buildup is an issue.

    *An alternative to BLO, is Tung oil. Another great drying oil used frequently in wood working. More expensive, much lower in VOC's. The Raw tung oil takes about 2-3 days to dry. Polymerized Tung oil, from Sutherland and Welles, dries in 24 hours.

    *The majority of the VOC's that one should be concerned about are in the solvents. The two most common of which are turpentine and orange oil/citrus oil/D-limonene. These are all natural but much more toxic. Use a respirator. Orange oil produces slightly less VOC's but is so much more pleasant to smell, but is therefore more dangerous. People tend to think, oh it smells good, it can't be bad for me, thereby getting a larger exposure to the VOC's.

    *If using Turpentine, go for the pure gum turpentine, if you can find it over the spirit of turpentine. Pure gum is the first processing using steam distillation. Higher quality, less VOC's. Spirits are solvent extracted and have a higher in VOC's.
    Oh, and the hard ware stores carry gum spirits turpentine. This is plain spirit of turpentine.

    *Carnauba wax is indeed harder. It works well. It's also white, instead of yellow. Thus if you have any small divots, cracks in whatever your sealing, the wax infill of these space will be white and more obvious than the translucent yellow of the beeswax. Beeswax is also local, Carnauba is almost always from Brazil. Try a mix of the two waxes.

    * is where you get more info on BLO w/o the driers.

    *Costs RLO $15/gallon BLO $14/g BLO w/ driers $24/g Tung oil $40/g Polymerized Tung $80-100/g

    * A good estimate for a 4-5 coverage is 1 gammon of each solvent and oil per 100 sq. ft. of surface to be oiled. This of course depends on how textured your surface is, how thick you apply, if you do the thinned coats first or last. So take it with a grain of cob.

    * oh and wheat paste sealers are ok, as long as they're not exposed to UV. They have a tendency to peel after a couple months.
    • ted
      offline 0

      Re: Linseed oil mixed into Cob/Earth Plaster mix?

      Sat, October 31, 2009 - 9:35 AM
      Just wanted to add a midwest flavor to this topic, since so many of the reference points here are out west (I did my time out there, love it, just don't live there).

      I live at Dancing Rabbit Ecovillage, where we've been doing natural building for 12+ years now. I was introduced to Linseed oil for earthen floor finishing, told about the heavy metal content in BLO, and aside from the first gallon of BLO bought before I heard about the nasties in it, I've used nothing but raw linseed oil ever since. Mostly on floors and as a wood preserver. I've never had any trouble with RLO, though I did have trouble with tackiness with too much beeswax content.

      We do 4-5 coats of RLO with increasing proportions of solvent (usually turpentine, sometimes citrasolve) in each for floors. Depends on weather and temperature, but it rarely takes more than a day or at most two for a coat to soak in. Also use this on stair treads and on walls around sinks and things. Beginning to focus on exterior use. Mechanical weathering of earth plaster outside is a challenge. Most here use lime wash or plaster for exterior, but I prefer the lower embodied energy and aesthetic of earthen.

      Now considering doing a kitchen counter in cob, and so focusing more on waterproof interior use. Anybody have any experience with the Steens' iron cob? I was glad for the advice above about mixing linseed oil directly into finish plaster rather than just using it as a finish, but I've heard iron cob can be used to make a sink if you want to, and that the rough idea is mixing dry powdered clay with linseed oil, no water.

      Any help?

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