How To: Use Boiled Linseed Oil (Safely)

By Scott Sidler • May 4, 2015

how-to-use-boiled-linseed-oilBoiled 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.

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

  1. 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. 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

  3. 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.

  4. 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?

  5. A standard recipe for treating exterior cedar cabins follows:

    1 gallon boiled linseed oil
    2 qts turpentine
    4″x4″ x1 1/2″ square of paraffin wax

    Melt the wax in some of the oil then add the balance of the oil and turpentine. Apply with thick brush or rollers. It should go on in sunlight with the oil mix heated. Lasts about 5 years in a very rough winter climate.

  6. I just bought a outdoor side table made of solid acacia hardwood & wanted to no what oil I should use to keep it protected from the elements. I live in florida so it’s hot, humid, & wet. Winters are not bad but once in awhile it drops down to 20’s. The table is already a darker strain & I wish to keep the current color in its matte finish. I’ve been reading about oils versus wax, UV protection & the list goes on & I feel like i’m spinning my wheels getting no where. What should I use that will keep my side table safe from elements, keeping the same look in its matte finish?
    Thank you

  7. I done my interior walls on my back porch with old palley boards sanded first will boiled linseed oil work good on the old pallet wood

  8. I am refinishing an old night stand and so far I have used Citristrip to take off the old stain and then mineral spirits to clean it. I then sanded it. I don’t want to stain it since I like the natural color. If I use linseed oil do I need to use a pre stain conditioner? Also after the linseed oil is there anything I need to do? Or should I just used pre-stain and then a clear coat?

  9. I have acquired a horse drawn training sled, unpainted, that has weathered quite a bit. From what I am reading, I am a little unclear if using BLO or even a BLO/turpentine mix to it is a good idea. This is not something that has to have a refined look, but we want to preserve the wood just the same. We may or may not be painting it afterward. I don’t want to invite a mildew issue as this will (obviously). Can someone guide me? Thanks!

    1. Regarding Nanci Richards,

      BLO will go black in the sun unless used with a topcoat that has UV resistant properties. I would recommend a SPAR VARNISH for any exterior work. To answer your BLO/turpentine question, all that does is thin out the oil making it easier to wipe on and dry. Be careful, you don’t want too much thinning. 1 to 1 is far as you want to go.

  10. I’ve recently sanded down a 10’x15′ deck of Douglas Fir to raw wood.. it had pealing/cracking varnish or polyurethane on it. It gets quite hot in the summer and the deck takes a beating. What would you suggest I protect it with? I’m seeing a theme of a mixture of equal parts BLO/Varnish/Thinner.. would that work on a softer wood like Douglas fir? I also see a lot of people recommending Epifanes but it’s quite expensive and not sure it’s really designed to cover a whole deck, maybe more for trim and smaller jobs? Thanks for any recommendations.

    1. What’s the answer here for a deck. My question in redoing pine deck steps can I apply linseed oil then when dry apply Thompson water proof ?

  11. Twenty years ago I installed a mile of barb wire fencing. Every 45 feet I used a wooden post. Recently I noticed the posts were very dry. I applied Thompson Water Sealer and the wood soaked up the sealer. However, a few months later I noticed the posts darkened but they still look dry. Would an application of Boiled Linseed add oil to the post and preserve the wood?

  12. I recently purchased a set of scaffolding for a project and instead of 2 X 10 planks I opted for the plywood and aluminum version as they are 19″ wide and have a capacity of 500 pounds.

    Can I treat the plywood with boiled linseed oil, or is there a better option available?

    Many Tanks for any replies.

  13. I have never done any wood work. But I am wanting to restain a second hand crib before my baby is born (meaning I have to find something suitable for me-being pregnant- to use, as well as safe for a baby, considering she will put her mouth/chew on the crib). I like the natural wood look. Is BLO safe? Also do you need to use wood conditioner before applying BLO and something after (sealant)? If you don’t think BLO is the best idea for a crib, could you suggest something else?

    1. I wouldnt… babies sometimes chew or suck On the wooden toprails of cribs and the chemicals in BLO could be an issue. Better to use a food-safe finish like those for cutting boards.

    2. Mineral oil is used on bare wood with good (healthy) results. I have been using it to maintain my wood handled knives for over thirty years; they look great and are perfectly safe. Years ago, when I was in Mexico I needed some mineral oil for my knives; I found it in ‘Baby Oil’ …that is how safe it is. It will dry out over time depending on usage and conditions, but reapplication is simple and easy…you can put it on your hands and all over your baby too!

  14. I want to clean and restore a 90 year old fretwork apostle clock. It was sitting in a hot dry attic for 15 years. Would BLO work well if I applied it with a good brush. How can I clean it with alI those hundreds of corners and recesses. I do not know what it was finished with but it looks like just a stain.

  15. I realized my 30-year old oak coffee table was a bit grimy, so I cleaned it up and now some areas seem too dry, so that the finish looks uneven (lighter/darker). Can I use BLO to even it out? Will there be an odor? Can I use Pledge to dust? Have been using it for many years and pleased with the results.

  16. I just got about 100′ of new redwood fence installed. What do you think about using boiled linseed oil straight to waterproof the wood and preserve the color? I’m in Northern California and we’re headed into our hot dry summer, but it can be wet if we have a normal winter. Will it be susceptible to mildew? Also, any thoughts on where to source the oil in quantities greater than 1gal? All the major hardware stores seem to just carry it in 1-gal containers. Thanks in advance.

    1. We use BLO at work every few years to refinish the wood decks of our backhoe trailers. Your fence will get less abuse than our trailers, so you should be fine. BLO will weather like any other stain, so you might as well try it. If in a few years you are not happy with it’s performance, try something else. I have never seen mildew on our trailers, and I am in northern Arizona. As far as quantities, you might try a contractor or farm supply. We just get the quarts from Home Depot.

    2. II have used linseed oil mixed with turpentine (1 pt oil:2 parts turps) on out door furniture for decades! a garden seat 42 years old looks almost NEW after total time outside ! I oil it @ every 3 years I spray onto fences it is easy to use a “airless” sprayer, do wash it out well or the oil may “gell” in the works! great stuff…. but Do Not leave the rags about as they may self combust , no prob with the wood , we have an extreme climate!

  17. We have some very old wood that we’re plained down for our bedroom floors . Is boiled linseed oil strictly good to use by it self or can we add a small colored stain to change the wood color just a bit . And is it OK to put a polyurethane over the boiled linseed oil ? We’ve been told to add turpentine or mineral spirits with the boiled linseed oil when we put it down on the floors and shelving to help with the drying aspect of it ….is this true ? Thanks

    1. I use a one to one part BLO and mineral spirits as a wood conditioner on my old quartersawn oak. It does change the color to a warm, slightly reddish color, which I love! Then I finish with an amber shellac which gives the wood that old arts and crafts color without fuming the wood!

  18. We live in a very old house and we pulled the carpet up to reveal a very dry floor. We used linseed oil in most rooms but now we have a baby and wondered about using it in the house now. Are there any dangers to the fumes? I know when we did the nursery when I was pregnant, it took months before the smell was totally gone (she didn’t sleep in there with the smell). Just didn’t know how long to wait before she can be in a room after we treat the floor. Ty!

        1. Definitely will still burn! Dry linseed oil won’t *spontaneously* combust like wet linseed oil rags will, but it won’t prevent the wood from burning at all. Very few organic materials are fireproof.

    1. The fact that you’re mentioning a smell makes me wonder if you used a linseed oil-based product, and not pure linseed oil. I’ve used regular and artist-grade linseed oil and I find the smell really mild compared to other stains, sealants, solvents and paints, and not something that lingers more than a day or two. If you still have the container or know what brand you used, it might be worth reaching out to the manufacturer about it if you’re still concerned.

  19. Hi Scott,

    I have a recipe for equal parts boiled linseed oil, Minwax satin wipe on poly and mineral spirits. I used it for hand carved projects. I have also used boiled linseed oil on a fairly large deep relief carving. Both treatments seem fine. Is there any advantages to the recipe version?

  20. Hi. We live in a very hot area in South Africa. We have raw barge board and balcony around a windy verandah. We have been given numerous advice and are now confused. We have a water based stain, an excellant water based varnish. Someone suggested we use linseed oil before we apply these two. Drying time is not an issue, we have loads of time. The question is can we apply water based over linseed?

  21. I wanted to try a different way to finish my pens and bottle stoppers besides using ca glue. So, I have been trying a combination of 1 part blo, 1 part denatured alcohol, and 1 part linsser clear shellac. Would I be able to use the same technique on bowls?

  22. I have inherited an old dining table that I wish to use daily and protect against water (precipitation rings) and heat damage from eating on it. Would BLO achieve this?

    1. No. It is not a good option for heat applications nor is it very good at protecting against moisture. Polyurethane would be a much better fit

    2. My parentes have an old oakwood dining table, which polished /rubbed down once a year with a beeswax based protective. This keeps the table quite well, but as a precaution, they always use coasters, for pots, pans and drinking glasses.
      I Hope this helps
      Kind regards
      Christoffer

      1. Agreed, as a traditional woodworker building cabinets and repairing antique furniture I strongly recommend a good rubbing of beeswax to a gloss every six months. If you don’t rub it to a very thin gloss though it will build up, crack and yellow. I recommend the medium hard amber wax.

  23. I just bought a house that has rough wood walls in the living room. They are beautiful and I want to keep them looking that way. Should I be using Linseed oil on them and if so how often?
    Thanks

    1. I can’t tell if what you are describing is reclaimed ‘barn wood’, roughcut mill seconds or what the ‘70’s market called ‘Pecky Cedar’- which really was cedar that was cut into planks from logs that had began to disintegrate. Either way there are several treatments available. The newest is of the modern polyurethanes that can be rolled on thin to a matte finish. A linseed oil finish which can be rolled on in several layers to suit taste. Or a fine sanding and waxing to a lustrous finish. In my own house I have harvested our own logs, cut our own planks and finished them to dark Edwardian style ceiling to floor French Polished (multilayered hand mixed lacquer) paneling. Basically, the more work you put into the project the more rewarding it will be.

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