Boiled Linseed Oil (BLO) is a common item in my shop and in a lot of woodworker’s shops. It is a great oil treatment for woods, leaving a smooth touch on the surface. It revitalizes old dried wood and gives it a new life.
BLO is often mixed with other finishes and was once one of the main ingredients in most paints. There are still companies that make linseed oil paints like Allback if you’re interested.
Boiled Linseed Oil is not actually “boiled” like the name suggests, rather, it is chemically modified to encourage faster drying. Slow drying oils are a good thing, but regular linseed oil can take weeks or even months to fully cure in cold weather and that’s just too stinking long. Boiled Linseed Oil will dry in only a few days give or take depending on weather.
As awesome as this product is for both wood and metal, it has some dangers (specifically flammability) that need to be addressed in order to use it safely. Let’s talk about safety first.
Boiled Linseed Oil Safety
The hard truth is that Boiled Linseed Oil can spontaneously combust if stored or used improperly.
“Why on earth would you use it then?”
Well, gasoline is a lot more flammable than BLO and I don’t hear anyone calling their cars a death trap (except Corvair owners).
Here’s what happens: BLO cures by a chemical reaction with the surrounding oxygen in the air not by evaporation like water based finishes. This reaction generates heat like most chemical reactions. The heat generated can be intense in certain circumstances and can lead to spontaneous combustion.
Larger amounts of BLO create greater heat. Smaller quantities generate less heat.
How to Avoid Fires
- Always store BLO in metal containers. You can pour it into plastic containers for temporary use, but for long term storage it should be in a metal container.
- Any rags soaked with BLO should be laid flat on a non-flammable surface away from flammable items until they are completely dry or they can be placed in a metal container with water.
The most common source of BLO fires is from a wadded up rag that has been soaked in BLO. The rag is wadded up and thrown in the trash with wood dust, newspapers or other kindling.
Since it is wadded up, it generates more heat because there is no air to pass over it and cool it. It then heats up to the flash point of the surrounding materials and the fire starts.
Watch this video to see how this happens.
//youtu.be/9yq6VW-c2Ts
Despite this issue, I still believe BLO is a great option for wood and metal. Read below, and you can learn how to safely use Boiled Linseed Oil.
Boiled Linseed Oil & Wood
BLO is a great protectant for wood both indoors and outdoors. It beautifies any wood and, once cured, protects the wood from sun and water damage. It can really reinvigorate old dried out wood and bring it back to a healthy status.
The powerful thing about an oil finish like BLO is its deep penetrating abilities. After application, the wood fibers draw the oil deep inside which protects not just the surface, but the whole piece of wood like in the image here.
Wipe on a couple coats of BLO on furniture, trim, or any bare wood and let it dry until it is no longer tacky (usually 24-72 hrs). The application is as simple as it gets and the results are more than worth the effort, which is why it has been used for hundreds of years by carpenters and refinishers.
Boiled Linseed Oil & Metal
A lesser known use for BLO is to protect metal from oxidation. You can apply a thin coat to non-moving parts and once dry it will protect and beautify the surface. Thick coats can get gummy which is another reason you don’t want to use this in moving parts which get stuck together.
I use it mainly for chisels, screwdrivers, heirloom tools, block planes, and more specifically cast iron tops of my “Big-Boy” tools in the shop like the table saw, mortiser, and band saw.
Sand off the rust and polish the metal with some 0000 steel wool, then wipe on a thin coat of BLO and you’re good to go.
Boiled Linseed Oil has one other thing that can cause concern, especially in humid climates. On exterior surfaces in humid wet climates it has a tendency to mildew. So, before you go coat all your adirondack chairs, test an area for a while and see how it does.
If you do get mildew, it’s not the end of the world as it can be easily cleaned off, but that’s why in Florida I prefer to use it mainly indoors.
Founder & Editor-in-Chief
I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.
A while ago I saw a article on using boiled linseed oil to revitalize dull vinyl siding. I have searched and can’t find anything that says if this will work. It seems the more you clean the siding the faster it gets dirty. Any thoughts on if this will help or could it ruin the siding. I live in the south where summers are hot and humid.
I have an all redwood house that appears to have been coated in linseed oil. I was thinking of pressure washing and trying to darken the color a bit more brown. Can a tint be added to the oil or is there another product that would be compatible. I don’t want a blotchy mess. Please help
I have stripped my sashes and doors with heat and chemicals and did sanding and filing and getting ready to print should I coat the barewood with BLO and let cure before I prime with oil based primer? or is the oil based primer enough. I have done the same thing with all the wood in my house – just wondering which step is next?
Debbie, you can treat old dry wood with BLO and give its few hours before priming with an oil based primer. That helps pull the primer deeper into the wood and makes for a better bond.
We are planning on finishing the inside of our log home ( White Pine, dried for approx two years) with boiled linseed oil. I was hoping to add earth pigment to the linseed oil, to give the walls a brown hue. Have you ever tried adding earth pigment to linseed oil? Do I need to add some additional binder to the oil in order to prevent the pigments from brushing off once the oil is dried? Thank you for your time!
I used BLO on my floor floor. It hadn’t been touch in 25 years.
Its been a week and there are parts that look like they are still wet and they are slightly stickey to touch. Looks like I may have put too much on? I closed the window and kept the heat on so it is normal temperature in the room. What should I do now? Will it eventally dry all the way?
Betsy, BLO will eventually dry, but if the coating is too thick it may take an extremely long time. It’s best used in very thin coats as a penetrating wood treatment. If you try to build up a surface it won’t work well. Try scrubbing the surface with mineral spirits to get the excess off and then starting over with a few very thin coats.
Also, if you had polyurethane on your floors the BLO is not a good finish option for you without sanding the floors to bare wood first.
I live in western Utah. High desert
country. Have a west facing small deck.
Can I seal it with raw BLO? This area
gets hot sun during summer months. If I
seal it now, will it be safe throughout
the hot summer months – even when very dry?
I’m not as well acquainted with your kind of climate but the biggest challenge BLO has is that it can cause mildew. In a hot dry climate I would think that issue would almost be non-existent. So, I think it would likely be a good application for it.
Should linseed oil be used on wood surfaces that have already been sealed with varnish or polyurethane?
Suni, the short answer is no. Boiled linseed oil needs to penetrate the wood to truly be effective and varnish or poly seal it up preventing this.
I just did 2 coats of boiled linseed oil on a large would slap it was dried and prepped with 320 then 400 most of it now is complete cloudy haze!!! Help any advice!! I now realize this was the most protective choice for a dining table. What do I do with the existing and what would be the next step for a better finish ?
For exterior wood we’re using Raw Linseed Oil (distributed by Viking in the U.S.) from the Swedish Allback company) for restoring the very old and dry wood of our 1860 farmhouse. It is magical. It seems to actually bring the wood back to life, even when used over old paint. The old paint becomes loose as the oil penetrates, making it easier to scrape off. It is expensive but you won’t have to ever do it again! Layers of old paint make the detail of old houses disappear in time. But modern paints will crack and allow moisture to get in behind it (NEVER use latex outside – it rots wood since there is no way for moisture to escape). Old fashioned linseed oil paint soaks into the wood, waterproofing it and it never cracks or peels. We’re applying the raw linseed oil first, then when it is completely cured we will use linseed oil paint. Even though it is humid here in PA during the summer, we think it will be fine since we’re also using the zinc additive Allback recommends.
We’ll keep you posted!
I also have an Old Farmhouse in southern Appalachia and was looking for a post like this! Peeling paint is revealing beautiful grated wood siding that I want to nourish and reveal. How did you apply the RAw oil (brush?) and is there any concern with flammability on a southern facing wood wall that gets hot in the sun? Did you apply the oil on top of the existing paint? Finally, where did you purchase the Linseed Oil Paint and how long did you wait after applying the raw oil? Thank You Thank You!! Cathy
Loved the combo of linseed oil and Old Masters Gel stain, which is oil based, may want a little more shine, could this be achieved with an oil based urethane? I am trying to make cheap luaun wood doors look gorgeous, above results were my first test, if not the gloss urethane will additional coats of BLO do the trick?
Adding a glossy polyurethane should work though additional coats of BLO will also add some shine.
I hope you didn’t put polyurethane over your BLO! Polyurethane is basically plastic and will defeat the advantages of BLO. Linseed oil allows the wood to breathe, and it will flex with the seasonal changes. Additional coats would be the best, but if you want the “polyurethane look” this can be achieved with shellac or varnish or wax.
I have 100 year old house,possibly original front door. I want to refinish it with stain. Should I use blo first? 4 seasons climate….thanks
Stain and then 3 coats of spar urethane is what I would recommend. If you decide to go the BLO route then stain first and add several coats of BLO.
I just used BLO on a newly construced piece of furniture, part was unfinished wood, part was primed plywood.first I stained with a water based stain and sealed with BLO. didn’t like the stain color so primed with water based primer..primed only a few hors after wiping off BLO..seemed mostly dry but surely didn’t have time to cure….will I have any issues?
how long after it rains must i wait before I use boiled linseed oil on a deck?
Steve, I don’t know if I would use it for a deck, but usually wait till the wood is dry to about 8-15% moisture content. Easy way to tell, is wait till its dry to the touch and then give it another day of dry weather.
Does the flammable nature then mean that wood treated with the oil is far more flammable as well, or does that stop once the oil is absorbed?
Tracy once the oil has cured the flammability is not an issue. It’s merely because of the heat generated by the oil during the drying/curing process that causes the potential for fires.
Tx for your Time Scott !
Cheers
Great safety tips, Scott! Now here’s a bit of interesting trivia. King Tut’s mummy is distinctly charred (it’s fairly obvious in photographs), and exactly why had been a mystery for a long time. But not too long ago, an Egyptologist finally figured out why: As part of the mummification process, his body was wrapped tightly in linen wraps, soaked in linseed oil. Furthermore, his sarcophagus was basically air tight. So, the resulting exothermic reaction created so much heat, that it charred his remains, though they say, without producing an actual fire, given the minimal amount of oxygen available in the sealed sarcophagus. So yes; the use of linseed oil and its attendant safety issues have been around for quite a long time! ~ John
Another question… I Will be using red cedar for my porche and tiles roof … Would one of those products be as good as what the industries want to sell me? I live in a 4 seasons climate.
Tx
Hugo, probably best to stick with and exterior semi-transparent stain like Sikkens for your situation.
What do you think of danish oil versus blo for doors or furniture? COVs?
Danish Oil is another favorite of mine but the ingredients Cary so much by brand that I prefer standard BLO.
Love your topics! Really great to see somebody about my âge interested in preserving and restoring .
Cheers!
Would BLO be a cost effective and good choice for 200 year old wooden floor restoration?
Thank you
Diane, it would be a very nice wood floor finish. It won’t be as hard as polyurethane, but will give a nice glow and give you a very “close to the wood” feel.