How to Thin Boiled Linseed Oil

With lovely blue flowers and long stalks, flax makes a beautiful field before harvest, and after harvest is used for a variety of products.  Golden oil is derived from the flaxseed and strong fiber from the stalks.  The flax oil was used for its nutritional value in diets, and the fiber was used in the making of textiles.

While the fiber remains in use in the making of textiles today, the oil came to be used to protect wood used in the making of furniture and flooring, for instance, and in the preservation of concrete and ropes.  Flaxseed oil came to be called linseed oil, but linseed oil often contains additives, whereas flaxseed oil can also be purchased in its pure form. 

This distinction is important because flax oil has nutritional value and is used as a dietary supplement high in omega-3 fatty acids.  It derives from a cold-press process and has a nutty flavor.  The additives most often used with commercial linseed oil are poisonous and should never be consumed.

What Is The Difference Between Linseed Oil and Boiled Linseed Oil?

In its raw form, linseed oil is slow drying, frustratingly so for those who want a quick solution to preserving and protecting their wood projects like doorsteps, furniture, or flooring.  The exceedingly patient woodworker might be happy waiting for a few weeks or even two months for it to dry thoroughly.

For those less patient, though, boiled linseed oil is the better choice.  Both raw and boiled linseed oil will penetrate wood fully if it is bare or has been previously oiled; paint, varnish, or wax must be fully removed before using linseed oil because they will prevent it from fully penetrating the wood.

Is boiled linseed oil actually boiled, though?  Sorta, kinda, but not really.  Boiled linseed oil is raw oil mixed with oil that has been heated by passing hot air through it and further processed by adding metallic thinners that act as a drying enhancement.

Using boiled linseed oil instead of raw linseed oil reduces the dry and finish cure time to 1 to 3 days, a big difference from 1 to 2 months. 

Dry and bare woods are sponge-like and take liquids easily.  After curing and penetrating fully into the wood, boiled linseed oil protects the wood somewhat from liquid absorption but does not make wood waterproof.  For that, an additional coat of something like polyurethane or varnish will be required.

Boiled linseed oil will leave a soft, mildly yellowing color behind, and in the absence of sunlight will darken slightly.  Because it fully penetrates new and bare woods, the protection runs throughout whatever it is applied to.

Does Boiled Linseed Oil Need To Be Thinned?

No, boiled linseed oil does not need to be thinned, but it can be without affecting its penetration and the protection provided by it.

Thinning it will reduce its viscosity and make it runnier, which will change the way it is applied to woods.  While undiluted boiled linseed oil can be applied with a brush or roller, thinning it makes it runny a cloth application will work better for you.

Regardless of how it is applied, remove any excess oil from the surface by wiping it with a cloth after about 15 minutes.  This will prevent a sticky surface.  After a full dry 24 – 72 hours later, give the surface a light sand (320 grit paper) before applying a second coat.

Two coats will give you proper protection for your wood, although 3 won’t hurt, either.  Allowing sufficient time for drying on the surface also allows for the full penetration of the oil into the wood’s finish.

Can You Thin Boiled Linseed Oil With White Spirits?

Yes, a small amount of white spirits ( a petroleum distillate)  can be added to it and used as a first coat on raw wood, a sort of primer.  But, for the second and third, use undiluted boiled linseed oil.

Can You Thin Boiled Linseed Oil With Mineral Spirits?

Mineral spirits, also petroleum-based, are a less expensive alternative to turpentine (vegetable-based) and can be used to thin boiled linseed oil.  They lessen the thickness of the oil and decrease the drying time.  Mixing mineral spirits or paint thinner with boiled linseed oil will also help protect outdoor concrete and stone from the freeze-thaw of winter and spring and salt and chemical (as de-icer) damage.  The ratio would be equal parts, 1:1.

Can You Spray Boiled Linseed Oil?

Yes, boiled linseed oil can be sprayed after thinning with mineral spirits or paint thinner.  It would save a lot of time, for instance, if you were using it on wooden fencing or an outdoor concrete or stone patio.

Boiled Linseed Oil is most often used inside, although we have suggested its possible uses outdoors as well in specific instances.  It is affordable and environmentally safe, and an easy finish to apply.  It enhances the appearance of woods and dries quickly.  It helps to preserve the wood and the appearance and beauty of a wood’s grain.

What’s not to like about any of this?  Keep it in mind for your next wood project.  If you have a month or two to wait between applications, use raw linseed oil.  But, if you want a quicker result, boiled linseed oil is the better choice. 

2 thoughts on “How to Thin Boiled Linseed Oil”

  1. Hi Matt – my partner & myself are trying to protect our indoor bare mahoghany stair handrails having stripped them of a previous orangey coloured stain & lightened the surface with wood bleach. We hadn’t forseen that the different lengths of wood would take up the bleach differently so we are now looking for something to even out the blotchiness as well as protecting the wood. Have tried using tea to add a little colour & eveness it has made little difference despite applying 5 coats. As we’d prefer to keep the wood lighter (as bare wood it looks like light oak) we bought some Furniture Clinic Boiled Linseed Oil thinking it wouldn’t add too much colour & tried a little under one of the rails but it has turned the wood a very dark brown. Can you please suggest anything that will protect the wood but keep it as light as possible while evening out blotchiness?

    • Have you considered Rubio Monocoat? For the most part, its the only finish I use because it is so easy to apply, available in a lot of different tints and simple to fix down.


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