How To: Use Boiled Linseed Oil (Safely)

By Scott Sidler May 4, 2015

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.

how-to-use-boiled-linseed-oil
Copyright: / 123RF Stock Photo

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.

 

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.

linseed oil penetration
Image Copyright: SolventFreePaint.com

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.

 

 

71 thoughts on “How To: Use Boiled Linseed Oil (Safely)”

  1. Can’t you put a mildicide in the BLO to prevent mildew? I plan to soak feshly machined/assembled windows sashes (Vert grain Douglass fir, that I make myself) in turpentine thinned BLO in a very shallow “tank” to achieve the penetration shown in your photo above. Seems to me a mildicide would solve the mildew tendency. Of course the exterior of the sashes will be painted, but the interior spar varnished.

  2. I am looking to finish the handle of a new axe. I was thinking about applying a coat or two of mahogany colored stain to the near-white hickory handle but am worried about the final texture. Obviously with axe handles you do not want a finish too slick, or something like a varnish which is too tacky. What would work best? BLO, stain, or something else? I want a bit of color and protection without loosing the texture of the wood.

      1. In the USMC (before the M-16 plastic stocks) we cleaned our M-14 rifles and coated the wood stocks with linseed oil. This was issued to us at the armory. I never had a problem with sticky, slippery wood stocks in any way. Rifle inspections, rifle ranges, etc., the wood stocks looked good and were protected very well. We cleaned our weapons weekly if not more often. I have never had a problem using linseed oil, ever.

  3. A handyman I used helped me disassemble an old Lutyen bench. We sanded all pieces, reassembled it and coated it with boiled linseed oil. It has turned black over the course of the fall and winter. I live across the bay from Mobile, AL in Spanish Fort where it is very humid. I just saw your posts about not using the boiled linseed oil in high humidity areas. What are your suggestions to get the mildew off and add a protective finish?

          1. But after the stain or even without (except for putting an extra character to the piece)? I thought of diluting the first coating with mineral spirit , than 3 coats tung oil …

            Best regards

  4. I am new to the use of blo, so before using it, i would like to check the advisability of using it on my kitchen cupboards, including the ones above the stove. I would like to also use it on a teek wood dining room table, and an oak bedroom suite. Unfortunately, I am such a novice that I am not even certain if there is any kind of sealer or shellac on any of these. So far, I have just been cleaning with murphys oil, orange glow, amish polish and similar products. I am wondering if blo would be a better more effective choice for the job. Thank you for your most valued opinion

  5. Hi Scott! Question…We just picked up our raw hickory butcher block island top from our cabinet maker friend. We decided to go with BLO to start but need a bit more protection so asking your thoughts on the final coat. We are thinking about using your beaswax mixture as the final coat or liquid carnuba wax (the kind with no additives) What would you use? My husband is contractor but using BLO is new to him. He wants to keep in “sandable” so he can re-sand in the future. Thank you so much for any advise!

    1. If you are planning to use the butcher block for any kind of food prep then the only option you really have is mineral oil. If you aren’t using for food prep directly on the surface then I would lean toward the beeswax mixture or a combo of even parts BLO, Mineral spirits, and polyurethane as a wiping varnish. With a few coats this generates an even harder finish than the beeswax.

  6. Would BLO be a good choice for refinishing a wooden outdoor swing? We live in the Houston area where the humidity is high in the summer months. If it is not a good choice what would you recommend? Thanks

    1. Outdoor wood is tough because it will need refreshing almost annually. BLO should be a good choice, just do a few coats initially and then a light sanding and a refresher coat once a year or so.

  7. Hi Scott re-doing a 100 year old stock wagon just got the wooden axels back from the amish would the blo be a great treatment for the new axels made out of white oak the wagon will spend most of it’s time out in the elements in the Midwest thanks for the advice

  8. Can you get BLO from Home Depot, Lowes or Menards? Sherwin Williams? I would like to use on a 2 tear old weathered cedar fence that has not been treated. can it be sprayed on?

  9. I live in LOG HOME and above the tub is wood. Do I just apply BLO to bring back the color and remove the water spots? Will I have to apply anything over the BLO

    1. Vicki, I would probably use a mix of BLO, turpentine and beeswax. Shave small pieces of the wax into the turpentine and let it dissolve overnight. Then add the BLO and apply to the wood wiping off the excess. This will give the wood even more protection against water.

      1. Thank you Scott . Question: for indoor ,on a new piece of furniture , to protect it a bit from water , would it be better than shellac?

        Tx for sharing your skills.

        Happy new year of health and passions.

          1. Thank you Scott ! One last question : do you use low cov or odourless turpentine? I am thinking of replacing the with lavender distillate or something else. I live in a cold
            Region and do not have the luxury to do my work outside or under a full ventilated room.

          2. I haven’t found an odorless turpentine but yes the smell is pretty tough even with ventilation. I have never used lavender distillate but I’ll have to look into it. I have found that the more expensive and purer turpentine don’t smell nearly as harsh as the cheap stuff though.

          3. I agree for the expensive turpentine. Much less odour . Will try it out. I am also looking for a higher quality BLO (still for COV and odour).

            Best regards

  10. My wife and I have a butternut live edge slab for a bar table. We want something to bring out the details in the wood. We also want a high gloss finish, so we were thinking of going with an epoxy on top. Is it possible to do the BLO as the first layer to bring out the details in the wood, and then finishing it off with epoxy on top?

  11. I have a mahogany side table that i rescued from a skip.. the top is badly cracked on the surface…. it looks like deep wrinkles..???? can it be repaired…

  12. We rented a sander and sanded our beautiful “distressed” 50+ year old hardwood floors. They looked very distressed and stains/scratches/ marks, but we loved them that way and chose to use boiled linseed oil because we could maintain it in spots as needed. It turned out beautiful after three coats. Then like big dummies we got insecure that the BLO wasn’t a sufficient sealer and added Johnson Minwax with a rented buffer. Now they look like crap. How can we get the oil off and is the BLO alone, sufficient sealant for our floors? We understand that using BLO means committing to maintenance. The ability to spot treat problems with BLO was a great appeal to us. We’re in a state of panic now. 🙁

  13. Hi, I was planning to use a combination of linseed oil and tar. I’ve found various recipes but what concerns me is the mixing it self. There seems to be vague instructions regarding the mixing but they do mention heat. I’d rather not blow up my kitchen so if you have any advice on this I’d greatly appreciate it.

    Thanks for doing this awsome page.

  14. 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.

  15. 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

  16. 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?

    1. 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.

  17. 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!

  18. 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?

    1. 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.

  19. 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?

    1. 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.

  20. 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 ?

  21. 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!

  22. 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?

    1. 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.

  23. 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

  24. 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?

    1. 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.

  25. 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?

    1. 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.

  26. 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

  27. 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

  28. Love your topics! Really great to see somebody about my âge interested in preserving and restoring .

    Cheers!

    1. 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.

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