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How To: Use Boiled Linseed Oil (Safely)

How To: Use Boiled Linseed Oil (Safely)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.

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.

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

    1. Safe for surfaces that will regularly come in contact with skin, yes, because BLO hardens when it drys and fully cures. Not for food prep surfaces like cutting boards, butcher blocks, etc because of the chemicals used in the heating process. For those surface, and depending on if the cabinet will see use in food prep, us BLO on the bodies and use Tung oil, mineral oil, or RAW linseed oil(which just takes crazy long to cure and dry).
      Hope this helps!

      1. Good old fashion shellac is great for wood that will come in contact in food preparation. Not very resistant to heat or large amounts of moisture, can’t handle standing liquid as it will leave rings or stains.

  1. How do I remove linseed oil from galvanized metal. I’ve been using a razor blade. Can you suggest an easier way?

  2. Would you recommend it for a porch floor ( not closed in but roofed) approx. 25 yrs old ; original stain all worn off.

    1. Depending on the condition of the wood, BLO can help revitilize old wood. I would recommend powerwashing, let dry, then sand(to expose ‘fresh’ wood) and thoroughly sweeping/shop vaccing to remove all dust, then several coats of BLO.
      for each application, allow the oil to soak in for a half hour before wiping off excess, then let dry for a day, then reapply. Sand after the second coat if you want to and then apply third final coat.

  3. I just picked up a trunk from the early 1800’s. It’s difficult to tell what kind of wood it’s made if, I only know there appears to be 2 different shades. A darker shade for the main construction of the trunk & another for strips across the top & around the sides. I want to restore to original glory. There is brass attaching the strips across & around the sides, as well as on the corners, latches & original lock. Can I use BLO on the brass??

  4. Just bought a house that was told to use Linseed oil on the exterior. Is it best to spray, roll, or brush on? I would think a sprayer would be quicker, but is it better. If a sprayer…what recommendations. If spraying is not an option, can we roll on?

    1. I’ve read that it’s best to use a mixture of BLO and Mineral Spirits or Denatured Alcohol (to thin it and help obsorption) And spray it on in a light coat (if it doesn’t soak in or lays on tbe surface you’ve used too much. If you plan to paint you’ll have to then use an Oil based primer.

  5. can I use linseed oil on a wicker lampshade that has dried out? After it has dried completely is there danger of the wicker catching fire from the light bulb heat?

    If it’s not wise to use it can you suggest another product?
    Many Thanks!

  6. I live on Guam which is very humid and hot. I have purchased a banjo and noticed that the inside walls of the resonator are bare wood. The back is black. I need to know if boiled linseed oil could be applied to the bare wood walls to seal them without changing the sound of the banjo?

  7. My daughter returned my parent’s rosewood nesting tables to me recently. They are minimum 65 years old with some intricate Chinese carvings. Two questions 1) there are some water marks, must I sand before using blo? And 2) should I use blo in the carving or just the flat surfaces?
    Thank you

  8. I have used BLO on a stool. Turned out great, only problem was the ants loved it while it was curing. No matter where I put the project to cure the ants would find it. Once cured, no problem with the ants anymore.

  9. I have a very old wooden wagon wheel that is very cracked and brittle. Would the BLO help this very brittle piece to plump it up? Someone suggested non-abrasive GOJO-any thoughts on that technique?

  10. I useed blog on cedar chest..3weeks..smell slowly going away..how can I speed it up..I can’t put the chest in house yet

    1. BLO finishes will often have a slight linseed oil smell for several weeks, even on compatible woods. That being said, as a general rule, you may not want to use boiled linseed oil on cedar, especially fresh cedar. Cedar wood contains natural antioxidants which can dramatically slow or even halt the curing process.

  11. I have several horizontal slabs cut through the trunk of an oak tree that has been estimated to be 800 years old. The tree was dead for at least 12 years or more before it was felled. I don’t know how dry the wood is yet and want to know if straight BLO is a good way to go, or should I cut it with mineral spirits. These slabs will be stored outdoors until I can start any finishing process.

  12. I can attest to the spontaneous combustion hazard of BLO having experienced myself. I was using cotton rag to apply coat to my front door and wanted to wait between coats so placed the rag on my plastic tool box in the garage. It was a hot day and the garage was hot which most likely accelerated the process. I went out to run some errands and got a panicked call from my wife telling me there was a fire in the garage! Thankfully, my quick thinking son grabbed the garden hose and dowsed the fire before it caused any damage. The rag had ignited and the heat from the burning rag melted through the top of the tool box. If my wife and son had not been home, well, the outcome would have not been good. It only took about 15 to 20 minutes to get ignition! Now I am extremely careful with oily rags. Opening them up to dry outdoors or soaking them with water and placing in a ziploc bag.

    1. Hello Dave,

      Oh my goodness! Thank you so much for sharing your experience! I’m so glad everyone is safe! These things happen so quickly and catch you off guard. Thank you for sharing so others can take this situation seriously and keep themselves safe as well.

      Thank you so much for taking the time to read The Craftsman Blog.

      Best,
      Alyssa at The Craftsman Blog

    2. How I can get read of dried linseed oil from furniture if I didn’t take out the excess after minute? It get like a glue, how can I fix it?

      1. try using a 0000 fine steel wool gently over the dried area. The only problem with steel wool is any metal fibers left behind will attract moisture and form rust spots. Some try Bronze wool also.

  13. Hi,
    I’m building in-ground steps using pressure-treated lumber and would like to treat the wood with whatever product would offer the greatest protection against the sun (full sun during daylight hours) and moisture. I’ve been told that boiled Linseed oil (BLO) would be a good choice but do not know how to use it. A few questions:

    1) Would BLO be a good choice?
    2) Can it be mixed before application with any other products such as Thompson’s Water Seal for added protection or with an oil-based stain for the desired color?
    3) In what ratio would it be mixed with another product?
    4) If mixing is not recommended, can an oil-based stain be applied later?

    Any additional suggestions you might offer are greatly appreciated.

    Thanks,
    Jeff

    1. The main ingredient inThompson is BLO. Adding more would be counter productive probably, diluting a well thought out formula.

  14. I live in AZ, with 100+ degree summers. Our house is just over 20 years old and has multiple 6×6 wood posts and cross beams holding up the front and back porch. I do not know what type of wood and I do not know if the posts/beams were ever stained or otherwise treated. The base of each post is encased in concrete, the wood does not go into the ground. Most of the wood is still a light brown, wood color, but all have areas turning the gray/black, dried-out color. Every piece is extremely rough; it looks like there are parallel vertical grooves in the posts that are 1/8″ deep. Inside these grooves, the wood appears to be cracked deeper. It’s too deep to sand down. I don’t know if this is a sign of deterioration in the AZ sun. I’m looking for advice on how to protect the posts and crossbeams in the future. I’m leaning toward BLO mixed with mineral spirits to soak into the wood. My questions are: I’ll need to use a brush to get into the grooves–how do I store the used brush for next time or do I need to get a new brush every Saturday? How do I dispose of/dry the used brush? I can’t lay it out in a single layer like a rag. Do I just lay it in the shade (or sun?) and flip it a few times a day until it’s hard? Since the grooves are so deep and I’ll be trying to smoosh BLO into the cracks, my BLO will be pretty thick. In AZ sun, is this a flammability issue, any issue other than long drying time? What are the recommended products for long term UV protection for exterior wood? I don’t want the shiny look of varnished furniture and I’m not painting the posts/beams.

  15. I have a redwood picket fence that has been painted white. The paint is peeling off throughout the fence. I want to paint it again, but this time I would like it to last longer. I live in SE Idaho where the winters are well below freezing and the summers can get over 100F. Must I strip all the paint off and then apply BLO first?

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