Last week, as luck would have it, I ran into a two natural builders tucked away in the hills of central Portugal. Lucky me; they showed me around their fabulous cob creations (not to mention plying me with vinho frisante and humous).
Take a look at this wonderful cob oven with cob seating area Frenk and Nicole built. It's gorgeous. But that's not the half of it. It's also water-resistant. The area containing the cob oven and seat isn't protected from the rain. Yet the cob has stood its ground.
How did they do it? They coated the entire thing in 3 layers of linseed oil. I'd heard about linseed oil from a few Mud friends in India where the stuff is cheap and easy to find, but I'd never tried it myself, because in Turkey the cost was prohibitive, more than organic olive oil!
"Yeah, it's not cheap here either," Frenk lamented to me, but good on him, he tried it anyway. "You heat the oil in a pan first, though not to boiling point. Otherwise the brush melts,” he explained.
Frenk and Nicole made their cob mixture out of clay, straw and sand. Initially, like me, they imported the clay. Then they realised the local earth was clay rich, and a glorious rust colour to boot.
Frenk is something of a rocket stove wizard, and has engineered another in his kitchen. If you want to look around it, check out the video. It’s very informative. The guy should have his own channel:)
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22/4/2017 11:46:14 pm
Yes, it is usualy used to protect outdoor and exposed wood, my friend used it for raised garden beds, no heating, two layers and at least 24 hours between them so it dryes properly. It is a must, otherwise planks would desintegrate due to elements. It's miracle that it can be used basically on earth as well.
23/4/2017 12:03:34 am
Also, with linseed oil [aka: flax oil]: The organic flax oil used as food, is very costly.
23/4/2017 04:18:15 pm
19/9/2017 09:05:12 pm
If your not concerned with organic you can recycle used motor oil to waterproof it.
23/4/2017 04:15:04 pm
Thanks for that tip Daniela.
25/8/2021 03:19:51 am
Oh..yes, the cost is high for non-preserved, raw linseed/flax oil. That is because flax seed oil is fragile…that is, it turns rancid real easy.
4/8/2022 11:17:27 pm
I have a silly question. I have just built a rocket oven and cobbed the base furnace all the way to the oven. Given linseed oil is flammable, could it catch fire as a sealant or do all the volatiles etc disappear once it’s used as a coating and dries? Just wondering if linseed oil on an oven adds an element of fire risk before I try it. Very excited about the idea though as the Cobb just melts away when rain hits it.
5/8/2022 03:13:11 pm
Linseed oil is not more 'flammable' than other vegetable oils, like olive oil, rapeseed oil, hemp oil, sunflower oil, etc.... Contrary to most vegetable oils, linseed oil is a 'natural drying oil', which means that this oil will take op Oxygen molecules from the air, connect this inside their molecular structure and in doing so it changes into a totally different product. Chemically spoken, this is a natural polymerisation (the molecules become longer).
5/8/2022 03:21:03 pm
Thanks very much for the comprehensive and easy to understand response Wolf. Very much appreciated.
6/8/2022 05:57:12 am
Agree with Wolf. put a roof over ovens. moisture will always be present and you dont want to seal that moisture inside, you want it to escape every time you use it.
6/8/2022 11:33:21 am
Maybe Erik, but when you’re in the open with nothing to attach a roof to, waterproofing is a good short term alternative worth exploring.
7/8/2022 01:11:09 pm
Super thread here. Thank you so much Wolf for this brilliant explanation. You've answered some questions I had about turpentine too. When is your book out? :))
23/4/2017 02:20:46 am
Linseed oil - I've used in through the years on various wooden items.
23/4/2017 04:19:39 pm
For the cob as I understood it, Frenk used raw and then heated it (I'd heard about the boiled phenomenon, hence I asked him if he boiled it). So perhaps the heating isn't necessary at all? Hmm. Experiments are needed:)
23/4/2017 02:31:35 pm
I have had good success water proofing masonry roofs by applying a clay-sand-lime plaster. then somewhat like tadelakt i press it repeatedly when it is leather hard. then several coats of lime wash. i imagine the moisture goes in some but even with repeated 8cm rains the mositure is not reaching the ceiling.
23/4/2017 04:21:07 pm
Now you've answered another question. Good on you Erik! I wondered what would happen if there was lime in the mix. Apparently it still works fine. Very exciting and useful news. Think it would work for a pool?
24/4/2017 03:43:36 pm
I also dont think it would work for pool. roots would be destroying it. as i said i dont think my roofs are water proof, but very water resistant
23/4/2017 11:54:16 pm
Think it would work for a pool?
24/4/2017 06:46:39 pm
Yeah, I thought it would end up seeping through. Really hard to find natural pool options. Clay also isn't enough when you're in a dry area and need to retain every drop you can get your hands on. The only answer is to live next to a river I guess;)
18/10/2019 09:30:49 pm
Ever think of a pool built like a cistern? So you enter through a door to minimize water loss...line the inside only with cement...not concrete but a fine, creamy layer of cement to make the inside of cistern/pool water proof....it was done similarly in petra...in Jordan
19/10/2019 02:00:38 am
I’d think slaked lime would work ok, as a water-holding layer inside a cistern, whether used only for cistern, or for pool. It swells up when wet, so should prevent much leakage; the swelling of it, from water, blocks water passing through it. Probly won’t prevent all leakage though. And, it won’t stop plant roots growing into it...,lime would be more as a coating, on, say, stone, block, or brick main containment.
25/8/2021 03:30:38 am
Oh..forgot bit of info. Years ago, I tried an off-brand of glue as an additive to plastering mix. It had similar consistency to Elmers white glue, except it was a bit thicker. No VOCs. Name: WeldBond glue. It was a general-use glue.
24/4/2017 11:35:24 am
Love this article and the tip for using raw linseed and heating it, I have used it to weather proof wood and other putty to glaze windows. Needless to say it has been imported from he U.K. In my baggage. As someone mentions above the boiled linseed oil you buy has chemical compound to make it go off quicker. The word boiled is totally misleading.
24/4/2017 06:48:14 pm
Yeah, there are some AMAZING cob floors. I can't imagine how nice they must be to walk on.
25/4/2017 02:29:08 am
Very nice find. I've found in a number of natural building books the recommendation for using linseed oil for earthen floors, which require a new coating every few years to stay durable and fresh. The application to walls sounds like a possibility, dependent upon the area of the world.
25/4/2017 03:50:53 pm
Your school project is fantastic. Well done Greg! I know how challenging it can be when funds are limited and far from resources. Your project has heart and soul. That's the most important thing. Take care there!
1/5/2017 11:41:05 am
I would stay away from cement in plaster on earthbag. i also used cement in plasters in years back but have come to read and experience they can cuase other problems down the line. i have earth walls in direct exposure to rain.
1/5/2017 01:30:54 pm
Yes I know. It tends to crack and fall off. Earth and concrete don't mix well at all because Potland cement holds onto moisture and isn't breathable. Lime is the way to go in wet climates. Trouble is It's not available everywhere.
5/5/2017 06:33:53 am
Greg, curious if rain is actually affecting your walls, even sideways wind. I have garden walls that go through 2 years of heavy rains. then get wet on the tops and dry in between. I see some two story cob houses that have only small deterioration after 15 years and only on one part of house. a tree right there would stop the driving rain.
25/4/2017 10:54:14 pm
Most vegetable oils will not dry. There are a few exceptions: linseed oil is one of them (toghether with tung oil and poppy oil)? This oil will take molecules from the air and change into a completely different product. This is why linseed oil is so extremely good. You can use raw linseed oil, but the process takes a very long time. Boiled linseed oil dries much faster and becomes better water resistent. You could do it yourself, but this is bloody risky, I can assure you! Vegetable oils are becoming very inflammable when heated and would you take the risk of your house burning down for just a few litres of boiled linseed oil? Our country (Flanders part of Belgium) has been famous for flax, linen and thus also for linseedoil and its technologies. We have excellent quality of linseed oils in different forms (raw, bleached, boiled, standoil etc.) for affordable prices. And 'preservatives' in linseed oil? No, this is not done. But there are siccatives available, those drying agents usually salts (uasually calcium, zirconium, zinc and/or iron) who will speed up the drying proces (they act like catalysts) but don't worry, they dissapear into the new chemical structure of the linseed oil. If you don't want to use this, just take raw linseed oil. If you heat it up just a little bit (please: be careful!) it becomes more fluid and will penetrate deeper into your cob (or wood, or stone or whatsoever).
10/10/2017 10:27:09 pm
11/10/2017 11:43:46 pm
If they got boiled linseed oil, well that's just perfect.
12/10/2017 05:49:07 pm
Thank you Wolf!!!! Very helpful and straightforward!
12/10/2017 09:18:24 pm
Yes, thank you Wolf for your generous sharing of your wisdom.
4/5/2020 03:35:16 pm
Hello Wolf - If you could answer this for us. We have built a cob oven - and will final treat it with the boiled linseed oil as described (we do have it under an open walled structure as well)... I would like to do the first coat 50/50 mix with turpentine to ensure the mixture penetrates effectively.. but am unsure about this as it is an oven - High temps.. should we just stick with the Boiled Linseed Oil? Safest bet?
9/7/2020 05:22:36 am
How is non-boiled linseed oil, or Shea butter, into cob, not turning rancid?
9/7/2020 05:48:59 pm
16/7/2020 01:25:25 pm
Thank you so much Wolf. Let me know when that book of yours is published:) There isn't much you don't know about natural oils and lime.
25/8/2021 03:38:37 am
Wolf Jordan, thank you for such great information!
30/4/2017 09:43:28 am
In Mexico they waterproof their adobe, cob or mud houses with cactus slime.
30/4/2017 11:26:54 pm
Yes I heard about that too. Wonder if Turkish cacti would have worked
4/5/2017 10:42:56 am
I know that this goes much against natural building principles but ... as we should also seek for ways to help industrial waste stay off from landfills, it kind of make sense. Any way. What if one used used motor oil to seal the cob? Would it work and would it be stable? I mean, has anyone tried it? Mud should bond with the oil so rain cannot wash it off to ground so it wont reach the groundwater right? So if it would work as a sealer for cob as well, it could be cheap option? Or what do you think?
4/5/2017 06:29:26 pm
Motor oil is a petrochemical product. Certainly when used, it will be full of really toxic elements. You get chemicals that evaporate as well as chemicals that will soak into the cob and into the earth as well.
4/5/2017 08:05:21 pm
Absolutely agree: motor oil, and other kinds of petrochemical-based oils and substances, = very bad idea on Cob, adobe, or straw.
9/5/2017 12:22:29 am
Thanks for the reply. I have not found similar discussion from forums and toughed that it is best to ask. My house is made of old tires, round wood, straw and COB. You can see it in here: http://www.thepoosh.org/buildproject/andres-andrekson/sassumaarja
9/5/2017 06:25:47 am
I think your last paragraph is the issue you need to look into. would engine oil change the cob properties in a negative way?
6/6/2017 05:58:12 pm
Engine or motor oil IS, simply a petroleum product thus is toxic and defeats the whole idea of natural building.
6/6/2017 06:35:39 pm
One final point (final - from me? you'll be lucky) when and if using linseed oil with or without anything else remember at the end of the day to dispose of all rags and cloths properly - on a rag that stuff spontainously (the Walrus dictionary works again!) combusts like crazy! Look the wrong way and a raging fire results, thankee for "listening" to this awld fool!
6/6/2017 11:42:37 pm
Ha ha, ah nice to hear from you Walrus. I especially was interested in the viking boat building info. So this would also waterproof a roof I assume. And if I make it down to Devon, I'll shall look you up!
7/6/2017 03:08:17 pm
Hi Atulya, it would be great to see you up here in Devon, but would you want to return to cold, wet England! I've just read my comment and yes it is true, proof reading has vanished . . . . . actually I never really had it! Thinking of waterproofing a roof, like all things a single entity would not do it, but used in conjunction with other items it would surely help and work well! the trick is to use many coats of the mixture and once in place maintain regularly to keep that coat whole! Buildings do as you know "settle" now and again and this cracks the coating which of course needs renewing, but it does not need renewing too frequently as to become a chore! Annually is normally adequate :)
10/6/2017 10:36:19 pm
About heating and cooking linseed oil, I quote mr. Walrus: "actually it's not so much the linseed oil that is the trouble but more the resins that need to be heated with it". Well, this is technically not so. There are no resins added to linseed oil. The drying process of linseed oil (and the other naturally drying oils) is, chemically spoken, a 'polymerisation', which means that the fatty acids start to form longer molecular structures. These are in fact natural resins. Those are all natural vegetable products. Plants take CO2 from the air thus reduce the quantity of carbon dioxyde in the air. Using plant matter helps us fight the climate problem. Telling this just to clear out the big difference with the synthetic resins and similar products, made from petrol...
10/6/2017 10:56:45 pm
Mr Jordan (Wolf) I think you'll find that depends on the process that you end up with. If you are making oil varnish you first need to heat certain resins together until they are liquid and then add linsed oil and maybe turpentine, there are many varied recipes. If you are making paint some are just linseed oil and pigment whilst others require heating, pigment added, strained and aged - as I said depends on the recipe! May I refer you to Stephen A. Shepard's "Shellac, Linseed Oil & Paint" for a start, that gentleman certainly knows more about the various processes than I ever will for a start, your knowledge may of course be greater (if so could you please refer me to any disentations you have produced on the subject - I would like to learn more on the subject) Many thanks the Walrus
11/6/2017 12:06:48 am
Well, Mr. the Walrus, the topic was on treatment of cob with lindseed oil. The making of paint and certainly varnish, that's another thing. I am in natural paints (linseed oil, tung oil, lime paints, lime renders, etc.) for some 38 to 40 years now and my grandfather was an artist painter (Van Tongerloo), so I gathered some experience on this subject. Conc. varnish, we have a traditional marine varnish, made of a mixture of linseed oil and tung oil. We don't do this preparation ourselves, it is done by a company, founded in 1839 and they still make this traditional product in the old way. The oil mixture is carefully heated under pressure and the natural oils are transformed into resins. In this case, no other 'certain' resins are used. Some types of modern synthetic varnishes use similar types of resins as our varnish, but made from petrol origin. But there is a big difference between both type of varnishes, believe me. Not only ecological differences but also technical. The varnish made of natural oils is more elastic. For this topic, I would never have advised to use even a natural based varnish, since this will stop the breathability of the cob. Raw linseed oil and even boiled linseed oil will still result in breathable layers. The shellac you mention, is not to be compared with natural oils, that's something totally different. I have given many lectures and workshops where I explain (at least my vision on) natural paints, but I did not write any dissertations. What I started to do is writing a book, where I wish to share my knowledge. Best regards, from the Wolf to the Walrus.
11/6/2017 01:02:33 am
Wolf sir, as with most "conversations" on the web in various places the subject had wandered slightly and I was under the impression that it was generally about the use of linseed oils in general following the old ways. Which is what I generally mentioned. As a mariner of some 37 years on various ships I became interested in the construction of paints and varnishes over the years however I merely dabble for my own entertainment (when I am not trying to set fire to myself!) The only mention of shellac I made was with reference to the tiltle of the book and yes to a certain extent it is different (made from the bodies of the shellac beetle mixed with denatured alcohol) but in some ways it can be as good as oil varnish - at least you don't have to heat the stuff! But it does require a lot of coats! It is however natural in every way! And Wolf when you finish the book you may consider at least one copy sold - to me! If I can find you when it is ready! (I wonder if Atulya could pass my email address on somehow?) Good luck with the book, best regards from the Walrus (and that's another interesting story)
23/9/2020 12:59:36 am
I am building with cob for the first time in Northern New York State. I plan to put a roof over the cob oven I am building, but was wondering if lime plaster or boiled linseed oil is preferable in a climate with hard freezes and at times drifting snow.
16/6/2018 11:06:59 am
Hello all! Wonderful to find you. I'm currently applying double boiled linseed oil on mud walls. After 2 coats the finishing seems patchy. All lot of 'viens' become visible and also some parts are shiny like varnished wood while others are dull. I waited 24 hrs between coats. Really looking for an even finish. What am I missing? Thanks!
16/6/2018 03:16:34 pm
It might be because of the actual plaster finish before you added the oil. If some parts were more compressed and worked smoother with a trowel, while others were left more porous, the oil will be absorbed unequally. But there may be another reason I'm not aware of, so I recommend posting your question on this forum: https://www.facebook.com/groups/naturalhomes/
15/2/2019 07:02:19 am
For me, the above tips and suggestions are really helpful in preventing water from entering to the crawlspace. definitely, I'll follow the mentioned ways
4/5/2020 04:13:47 pm
A reaction for Arlene Saunders:
7/7/2020 02:42:11 pm
Thanks for sharing!
18/11/2020 09:16:55 am
Nice Article...Very interesting to read this article. I have learned some new information. Thanks for sharing.
22/4/2021 09:15:59 pm
I have read the correspondence above on waterproofing cob, it was most interesting.
22/4/2021 09:42:26 pm
Please note that motor oil really is toxic.Above you find reactions from several people confirming this.
24/8/2021 09:22:09 pm
Hi beautiful people,
27/5/2022 04:55:49 pm
Oh great! It is really possible to make something waterproof. It is my first time to know about this. I am going to research more about this linseed oil and how to use it more. Thank for sharing this informative ideas.
17/10/2022 02:06:03 pm
Great explanation, Looking forward for more blog like this.
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