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Home > Finishing

Should you heat your linseed oil before applying it?

To heat or not to heat, that is the question!

I received a question from Rob this week after he received his Finishing Myths:  BUSTED! article #8.  This is the article where we talk about how some woodworkers swear by heating linseed oil before applying it to the wood.  This is suppose it help the oil penetrate deeper due to the heat making it thinner in viscosity.  This in turn should produce a richer looking finish.

Rob is a firm believer in heating his oil finishes before it's applied to wood.  I have never tried it and just took the word from an author and finishing expert that I respect a lot, Bob Flexner  He states that heating oil doesn't help it to penetrate deeper.

So, I decided to do a little experiment of my own to see which camp is right.

Here's what I came up with.  I used two methods of testing.  First, I took a piece of popular dowel and cut it in two parts.  One part I put in a cup of room temperature boiled linseed oil, the other in a cup of linseed oil heated to 120 degrees.  Both cups had equal amounts of oil.  I let the dowels soak in the oil for 20 minutes.  I then removed them and wiped the excess oil off and laid them aside to cure.

The second method of testing I chose was to simulate how you would normally use linseed oil to finish a project.  Taking a piece of white pine, I coated one end with room temperature oil and the other end of the board with the heated oil.  I kept the oil "wet" on both ends for 30 minutes.  After that, I wiped the excess off the boards and laid them aside to cure.











The curing time for both testing methods was 18 hours.  I took the dowel, and using a dozuki saw, cut out a cross section on each. (The line you see on the dowel in the picture below is the kerf of the blade.  I had to cut deeper than I though I'd have to!)  I did the same cross section cut for the pine board.

Here's the results:














As you can hopefully see from the pictures, there's no clear winner.  I could not see any difference in depth of penetration of the oil in either group.

So you might speculate that it's a complete waste of time to heat an oil finish.  Maybe, maybe not.  This was just an experiment to see if there was a difference in the depth of penetration of oil if it's heated.  From the outcome of the two testing methods I would have to say no.  However, this experiment doesn't take into account one important characteristic, the look of the wood.  This is a personal preference and one that I can't make a call on for you.  I could have used a nice piece of cherry in the experiment and then preceded to tell you which "looked" richer and had more character.  But, I would only be expressing an opinion (which is worth what you're paying for it!)  

Bottom line:  If you're heating boiled linseed oil to get better penetration into the wood, you're wasting your time.  However, if you're heating oil because you see that it gives the wood a deeper more pleasing color, then you're crazy not to do it.

-Craig Stevens 


P.S. If you'd like your own copy of our special report, Finishing Myths: BUSTED!, go to the home page and sign up! It's yours Free!