Finishing Cob with Linseed Oil

How many square feet of smooth cob (as on an RMH mass) would a quart of raw linseed oil cover approximately? Would one application be enough for good results? If not, how many are needed?

I know nothing about cob, but the key with raw linseed oil is very thin coats.
The 'drying' is oxygen-mediated cross linking of the fatty acid chains.
Thin coats allow the reaction; thick coats lead to a gummy mess.
As I recall, old plasticine is clay + linseed oil and it stayed flexible for a long time.

If you want to preserve specific cob walls against wind-driven rain, snow and wash-outs, you can use boiled linseed oil to coat it your wall.
WARNING: do not apply it to all your walls, because they will no longer breathe!
It will create a moisture barrier, trapping moisture inside if you treat al your walls this way.
You may finish it of with beeswax, in paste form.

Firstly you need to use boiled linseed oil.
Thin later coats with turpintine, I am not sure if you use mineral or pure turpintine.
I will read more books.

Here is a great video

“Not far enough” is always the answer about buying the small container of paint or finishes.

Instructions found for coating a floor in an Ianto Evans book:

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. (In some countries, Mexico, for instance, earthen floors are stabilized using old motor oil. While this might be okay for a well- ventilated space such as a carport, it will give off toxic fumes, so we can't recommend it.) Apply each coat until it begins to puddle, then wipe off any excess. The first coat should go on full strength. Wait for it to dry before applying the next coat. The second coat should be thinned with 25 percent turpentine, citrus thinner, alcohol, or mineral spirits. The third should be 50/50 oil and thinner, and the fourth 25 percent oil, 75 percent thinner. The reason for this is to improve penetration so you don't end up with an eggshell-thin hard layer on top of your floor, which can chip off to expose soft earth beneath. As each layer of oil is applied, it clogs up the open pores in the earth, which the water left behind as it dried, making the surface harder for the next layer to soak in. Warming the oil or the floor before application makes the oil penetrate better. When your final coat of oil is dry, which may take many days, you will have a hard, durable, water-resistant floor. Pour a little water on it and try scrubbing with your fingers—you will find that the water stays clean, but soaks into the floor slowly. Your floor is now functionally finished, durable, and attractive, but if you want to be able to clean it with a wet mop or spill colored liquids with- out staining it, you will have to wax the floor.

John C Daley wrote:Firstly you need to use boiled linseed oil.
Thin later coats with turpintine, I am not sure if you use mineral or pure turpintine.

What effect does the boiled linseed have vs. raw? This is for the mass bench of an RMH, no exposure to liquid outside of humidity in summer and an occasional, small spill.

Neither myself nor my clients are interested in playing the where/how much game with VOCs, so won't be using BLO. I have citrus solvent to mix in with the raw linseed oil if that is required for finishing coats...

This showed up in "similar threads":
https://permies.com/t/24631/Linseed-oil-coverage#196197

~35 gallons for a 500 ft^2 floor, 4 or 5 coats.

Pulled from another RMH thread, provided by Gerry Parent:

Although not a floor, the following is useful info you might like to know. Adjust as you see fit.
Some advice from the book: Earthen Floors by Sukita Reay Crimmel and James Thompson

- "One gallon of oil will cover 35–45 square feet, usually in four coats. Make sure there’s enough oil to complete the job, as all the coats are applied on the same day (the oil does not need to dry between coats). It can be applied with either a brush, a paint roller, rags or a sprayer.
- Each coat will require progressively less oil to cover the floor. The oil pattern is easy to see during the first coat. Pay close attention to where you have oiled with the next few coats. Darker areas have more oil than lighter areas. A brush tends to apply more oil than a roller or rags."
- The whole floor may show darker and lighter areas, and possibly even spots where oil has dripped off a bucket or brush. These irregularities will typically balance out and not be noticeable once the oil has dried.
- Apply oil until the floor is saturated, usually about 4 coats. The saturation point will become apparent when the floor stops absorbing oil, and oil starts puddling on the surface, usually in an irregular pattern.
- Stop applying oil to the areas where this occurs."

Coydon, from https://www.furnitureclinic.co.uk/blog/raw-vs-boiled-linseed-oil/
"Raw vs Boiled Linseed Oil
Raw Linseed Oil is the purest form of the oil, extracted from the flax seed and sold without any chemicals, solutions, or additives to preserve it. This is perfect for oil-based paints as it allows them to completely level and set properly, giving a smoother finish. However, slow drying times often limits the use of Raw Linseed Oil to items where drying time is not a consideration.

Boiled Linseed Oil is regular Linseed Oil that is treated with hot air and additives so that it dries quicker. Unlike the name suggests, it isn't actually boiled!

Linseed Oils are a traditional option for nourishing and protecting wood, but which is the best one to use? Once dry both oils will provide a similar level of nourishment and protection to the wood and they will both slightly darken and enhance the woods natural grain. But since regular Linseed Oil can take up to three days to dry, we always recommend using Boiled Linseed Oil when it comes to oiling all wooden surafces.

Boiled Linseed Oil still isn't a super fast drying oil, taking upto 24 hours to dry, but compared to Linseed Oil it is lightening fast! If you're looking for something faster, take a look at our full range of Wood Oils. Or, if you don't know what oil you need, read this post compares them all - Wood Oil Finish blog post.

Our Boiled Linseed Oil
After vigorous testing and research, we believe Boiled Linseed Oil is a superior quality oil. It can be used both indoors and out, on hardwoods and softwoods, and on furniture, flooring, doors, worktops, window frames and on pretty much all other items made from wood.

Not only has it been treated with hot air so it dries quicker, but it also helps prevent drying and deterioration, and forms a tough, hard wearing finish that imparts a natural lustre. Take a look at our video showing you how to apply it..."

Don't hate me but, what about silicone spray?  Yeah, I know it contaminates everything around if you spray it, but a little prep and you're good.  It sheds water, dirt and dust, yet it will allow the cob to breathe.

The problem with silicone (aside from the toxic gick aspect) is that once it's on there, you'll never be able to get anything to adhere. The thing about cob is that it's super easy to patch cracks and chips, or mold new features. If you introduce a material that prevents this, you've just wrecked one of cob's best attributes.

Phil Stevens wrote:The problem with silicone (aside from the toxic gick aspect) is that once it's on there, you'll never be able to get anything to adhere. The thing about cob is that it's super easy to patch cracks and chips, or mold new features. If you introduce a material that prevents this, you've just wrecked one of cob's best attributes.

That's true; I hadn't thought about having to patch cob.

Phil Stevens wrote:The problem with silicone (aside from the toxic gick aspect) is that once it's on there, you'll never be able to get anything to adhere. The thing about cob is that it's super easy to patch cracks and chips, or mold new features. If you introduce a material that prevents this, you've just wrecked one of cob's best attributes.

Patching is definitely a concern. Do the coats of Linseed oil have any effect on that? If the surface with an oil coat is repelling water, how do you get the new material to adhere over the crack?

This summer I finished a small floor in my greenhouse--about 300 square feet. It took 7 gallons! The floor just kept sucking it in. I applied it full strength--did not dilute it although I have done this on another floor in the past. I think your going to need another gallon or two depending on how big your RMH is.

Another interesting byway on this question that I came across was the relation between Flax oil and Linseed oil. I pulled this from Reddit, but it seems helpful nonetheless...

FrogFlavor
I wonder if linseed is just a bonus from flax grown for the purpose of textiles. I wonder if flaxseed oil (same thing but sold in grocery stores for food) has the properties OP is looking for.


forgeblast
It does, same plant just different varieties. The flax was grown for fiber and the linseed grown for oil. I use organic flax seed oil. But I make stand oil out of it. I buy it bulk in gallons, and put it in mason jars. 50/50 oil to water. Shake it once every day. Pour off the good oil. Do it again. Three weeks total. When you're done it's really pure oil. Dries quickly and I use it on carved spoons cutting boards etc because it's a drying oil vs mineral oil that never dries or beeswax and mineral oil that is melted the first time you use it.


Midnight-Meat-Man
I've never heard of mixing oil with water for purification and I can't find anything after some brief googling.

Does this method have a name & can you explain what's happening or send a link that goes into detail on the process?


forgeblast
Here are two links, the first is the one I followed. I would buy my oil from https://bulknaturaloils.com/

http://www.realcolorwheel.com/washlinseed.htm.

https://danieljamesyeomans.com/how-to-make-sun-thickened-linseed-oil/


lewisiarediviva
You harvest differently depending on if you want an oil or a fiber crop; the best fibers come when the plant is still green and flowering, but you don’t get seed. If you wait for the seed to be ripe and oily, the fiber is lower quality and harder to process.


obscure-shadow
I use flax oil from the grocery store for my wood handled tools. I don't go through enough to give an objective opinion as to the current quality though, I still have the same bottle from last year and it's fine

Short answer - - - I haven't a clue.

PSA answer - just be aware of fire hazards around using linseed oil.

Denice Moffat wrote:This summer I finished a small floor in my greenhouse--about 300 square feet. It took 7 gallons! The floor just kept sucking it in. I applied it full strength--did not dilute it although I have done this on another floor in the past. I think your going to need another gallon or two depending on how big your RMH is.

From coating my outdoor mud stove I found that new layers of mud will stick to old layers of linseed oil very well.
I do layers like this intentionally.
What mud doesn't stick to is powdery stuff like drywall plaster.

Coydon Wallham wrote:Another interesting byway on this question that I came across was the relation between Flax oil and Linseed oil. I pulled this from Reddit, but it seems helpful nonetheless...

FrogFlavor
I wonder if linseed is just a bonus from flax grown for the purpose of textiles. I wonder if flaxseed oil (same thing but sold in grocery stores for food) has the properties OP is looking for.


forgeblast
It does, same plant just different varieties. The flax was grown for fiber and the linseed grown for oil. I use organic flax seed oil. But I make stand oil out of it. I buy it bulk in gallons, and put it in mason jars. 50/50 oil to water. Shake it once every day. Pour off the good oil. Do it again. Three weeks total. When you're done it's really pure oil. Dries quickly and I use it on carved spoons cutting boards etc because it's a drying oil vs mineral oil that never dries or beeswax and mineral oil that is melted the first time you use it.

I'm told that fibre flax is taller-growing, more favourable for long fibres; while seed flax is a shorter plant devoted to flowering.