Oil + Varnish: together or separate?

[DaBear]

I've recently gotten into woodworking again after a 20-odd year hiatus, and have been doing a lot of reading on finishing (which has generally been the bane of my existence, hence the research), and have started using BLO as an experiment on a few of my latest creations (new workbench, some bowls, etc..).. In some of the materials out there, I see mention of 'oil/varnish blends', often 1/3 oil, 1/3 varnish/ 1/3 turpentine (or some other thinner) as a 'does it all' type finish.

Now, I can see on some levels that mixing a penetrating finish with a film one would in theory give both, but to me you'd be better off doing a coat or two of oil, then put a layer of full strength varnish on top once the oil is WELL cured. My logic is this: The oil is meant to penetrate, so let it do so. The solids from the varnish are not going to help that, if anything they will get in the way, and they will mostly get wiped off anyway, leaving a minimal film. Also, if you want to put a second coat, I would expect the film from the first coat to pretty much have sealed the wood, thus causing no oil to get through, meaning the second coat is just an expensive, thin 'wiping varnish'..

To me, for example if one were doing a '3 coat' schedule of this, you would be better off doing two coats of straight oil in order to get nice, deep penetration, followed by 1 coat of varnish to get a nice film for protection. My theory is to let each type of finish do what it is best at, as opposed to (at least in theory) make the two compete with each other..

Since I've seen the 'mixed' finish methodology pushed by so many, including some obvious experts in the field, I have to wonder if:

A ) Am I just missing something (which would NOT surprise me)

B ) This is perhaps something that sounds good, but people have never really thought it through like this..

Has anyone ever done a comparison?

Thoughts?

[thewoodwhisperer]

Hello Mr. Bear.

You'll probably find a lot of differing opinions on this. Here's mine.

"Penetrating" is just one of those pieces of marketing jargon that gets people to buy a particular product. Its kind of like the term "sealer". The first coat of ANY oil-based finish, technically is the sealer. And likewise, the first coat of any finish will "penetrate". Subsequent coats will continue to penetrate until the wood is completely sealed. So all of these finishes will penetrate into the wood fibers to some extent. Does BLO penetrate any more than a varnish? Personally, I think how far it penetrates is more a measure of how thin the material is than whether its pure oil, a blend, or pure varnish. This is why you'll frequently see finishing regimens where the first coat is thinned by 50% or more to make that first coat penetrate deeply. And if you were to take a microscopic look at a cross section of different finishes, I think you would be hard pressed to find a significant difference in penetration. This is just an educated guess by the way.

So if you are one that believes these products all have potential to penetrate equally (assuming they are thinned properly), it then becomes a question of what you want to live down in those fibers, oil or varnish. Since there is no question that a varnish is more protective than an oil, I would much prefer to have varnish embedded in those fibers. It makes for a nice base layer of protection for you to build a film finish upon. This is all assuming protection is your primary goal.

Now when it comes to an oil/varnish blend, I don't really think penetration is much of a concern or benefit. Again, thin it out and it will penetrate just fine. What the oil does is makes the finish easy to apply. But instead of being an oil alone, you get some protective benefits from the varnish that comes along for the ride. And since the oil component doesn't really cure well if the wood is already sealed, you usually want to stop after about 3 coats with this type of finish. Furthermore, people who use these blends are usually looking for a more "natural" finish anyway. So more than three coats and you'll start building so much film that you may as well just use a straight wiping varnish.

Not sure that cleared anything up. haha. There are a ton of ways to skin this cat. Frankly I think most of us have our favorite regimens that work for us, using all kinds of variations on the same theme. And realistically, the finishes probably come out looking pretty similar when its all said and done. So whatever gets you from raw wood to your "perfect finish" is definitely the method you should use.

[DaBear]

Hmm, an answer I have to think about.. DARN IT!!!! :-)

Thanks for the great response, definitely something I'll need to ponder for a while and maybe do some (semi) controlled tests.. I'll let everyone know if I find anything interesting (when I finally get to it..)..

Regards,

David

[thewoodwhisperer]

Please do! We LOVE finishing tests.

[bois]

I can't remember, have I ever mentioned an oil and wax finish in here? LOL

Following up on Marc's point, I believe the viscosity of the first coat is the reason people like to thin their "sealer" coats. A thicker heavier oil simply won't soak as deeply into the pores. I did an experiment in a video blog post not too long ago that demonstrated how a heated BLO coat does actually penetrate deeper into a closed pore species (cherry). You can see that experiment here.

[DaBear]

And this is why I think this 'Interweb' thing might actually take off

In all seriousness, that is some GREAT info, Rob. I'm not surprised that the heating helped, but I'm certainly amazed at how much of a difference it made.. To me, this is obviously a better method than simply thinning, as you are actually getting more of your 'product' into the wood that will stay and cure, as opposed to just getting a bunch of thinner deep in the wood that's just going to evaporate again anyway. Presumably, the thinner should 'pull' some of your oil in, but I would submit it would be substantially less than using the heated oil method.

Have you ever thought of doing the same experiment with tung oil? If not, I might to see if it has similar effects. Logically it should, as heating pretty much any oil will lower it's viscosity. I would think that the key would be to ensure you didn't heat it enough to start chemically altering the oil..

Arggg, more thinking......

Regards,

David

PS: Great jewelry box.

[bois]

I have not tried the heated oil experiment on any other oils yet, but I may have to try that on my next project. My guess is that as long as heating doesn't chemically alter the oil, or get it anywhere near its flash point, the same effect would be true. You get more molecules of oil deeper into the wood. And the way Moser describes it, oils do eventually "case harden" over a period of time, and create much more of a protective finish than most people think. There is another thread going on in this forum right now about how shellac is also more durable than most people give it credit for, so I'm thinking if you did several coats of heated oil followed by a shellac top coat and some wax, you could end up with one heck of a durable 100% natural finish. Hmm, I feel like there may be a blog post in the making here...