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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. Hi Scott! I am helping a wonderful old cedar double porch rocker. It is very thirsty from years of sun and air and use. We decided to go with the BLO. It looks great but I only did one coat. I plan do do another. My concern is: Will the BLO come out of the wood and soil your clothes later down the road, like on a hot or humid day? Or once 2-3 days has gone by is the BLO soaked in and there for the duration? Thank you for your service to this amatuer.
    Angel

  2. I’ve used it on my Axe and hammer handles for a while now and now I’ve become curious about it. What do you think will happen when I leave a Handel submerged in it for 24 hours? Well I’m about to find out because I just did so and now im waiting.

  3. My year old deck rail has signs of mildew. I’ve received conflicting information on prepping wood for BSO. Clean it with the bleach based deck cleaner, rinse, dry the apply BSO. In contrast, do not use the liquid deck cleaner – just sand lightly and apply BSO.Deck rails and side panels are cedar. Please advise

  4. We have mahogany flooring on our open porch. The porch gets full sun, rain and snow.
    The floor is about 20 yrs old; my husband has sanded off whatever was on the floor, so we’re working with a clean surface.
    Do you recommend Linseed Oil to rejuvenate and protect our mahogany porch flooring?
    If yes, do you have any suggestions for applying the oil.
    If no, do you have any suggestions for what to use on our mahogany porch flooring?
    Thank you,

  5. Will linseed oil (or BLO) cloud with heat? In other words, would it be a good finish on a wood kitchen table or would the finish cloud from heat transfer? Is there a better oil finish for this solution?

  6. I just bought an old double barreled “wall hanger” shotgun which is pretty rusted but still a great looking piece. I want to restore it for display and wondered if boiled linseed oil would be appropriate for the metal surfaces after cleaning and polishing them?

    1. I used it on my great-grandfathers axe that i keep as a well hanger and it works/looks great. Sanded the handle and polished the axe head a bit and put on several coats over a week or so. Still looks great after more than a year

  7. I have a question I haven’t been able to find an answer to. I made a wax compound using beeswax and BLO, but it came out a bit too thick. I heated the wax, let it cool a bit, then added the BLO.
    Would it be unsafe to reheat the mixture to liquid again and add a bit more BLO to get a more workable consistency, or is that prescription for disaster?

    1. You can add a little paint thinner to that mix, and then you’ll have a traditional “blacksmith” finish. If you warm it up to a liquid state, then (slowly) add a small amounts of turpentine, or paint thinner it’ll help to keep it In a liquid state longer. If it solidifies just warm it back up, and it’s ready to use. Just use caution when warming anything flammable.

    1. mixing with spirit makes application easier and penetrates the wood better, after the spirits evaporate the oil will cure as normal

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