what oil does?

[Trackman]

Does putting oil on wood as a finish help to keep the wood from warping? I have some walnut that I resawed an planed down to 1/4" an finished the project with clear poly spary. After about two weeks in the house the wood has warped about 1/16"- 1/8" enought to see. I don't know how long the wood has been cut from the tree but seemed to be dry when I was working with it.

Do you use oil than cover with a poly or other coating?

[shadowfx97]

As far as I know, no oil will prevent warping. If you could put a completely waterproof coating on all surfaces including end grain, you would have a chance, but I don't know of an oil that is completely waterproof.

[Bill Wilson]

Warping can be caused by a variety of factors. It may be due to how the tree grew. Trees that grow on hillsides or in high wind conditions may have inordinate stresses within the wood fibers. Milling of the wood can release these internal stresses and cause warping, cupping and twisting. Also, how is the wood sawn? Flatsawn wood is inherently less stable and more prone to cupping/warping than quartersawn wood.

Another common factor is uneven drying or release of moisture. Air dried wood will generally reach somewhere around 12% - 18% moisture content. Kiln dried wood will generally go under 10%. However, wood does acclimate to it's environment, so even dry wood will absorb some moisture if it is moved to a humid environment, after it has been dried. To keep it stable, conventional wisdom is that one should allow wood to acclimate in the shop environment for a period of time (varies, depending on conditions), before milling.

Another theory is that if you plane more material off of one side of resawn stock, it could affect moisture transfer and the wood becomes more prone to cupping because one surface is releasing/absorbing moisture at a different rate than the other. It's recommended that one should remove roughly equal amounts of wood from both surfaces when planing stock.

As for oils and finishes, about the best advice I can offer is that once you follow good practices in storing, acclimating and milling stock, it's best to apply finishes to all surfaces of the wood, once the project is built. This prevents the uneven transfer of moisture that I mentioned above, re planing. It really has less to do with the products used than the process itself.

Back in the day, because finishes were expensive, furniture makers wouldn't "waste" the product on surfaces that weren't visible, so it is common to see antique table or desk tops with no finish on the bottom. However, generally speaking, 100+ years ago, more of the wood was old growth, which leads to another factor in wood movement. Wood with very tight growth rings (old, slow growing trees) are much more stable and less apt to warp than woods today that are harvested much more quickly in the growth cycle. Some commercial tree farms have genetically engineered wood species that grow faster, in order to speed their time to market and increase profits. This is a big reason why construction lumber seems to be so much more prone to warping than it was decades ago.

Sorry for the long-winded answer, but what I hoped to make clear is that there is no single solution to solving the problem of wood warpage. It's a combination of several factors (some of which are out of your control) and if any of those factors work against you, all the efforts put into the others may not prevent problems. Some of it just comes down to luck. Hope this helps.

[Trackman]

Thanks Bill for your great post on warping. I had didn't know about all of these different factors.

As for finishing, what is using oil for? (personal choice for looks or function) Many thanks!

[Mick Walker]

Trackman, most people use oil to enhance or pop the grain. Pure tung oil takes forever and a day to dry. Boiled linseed oil (BLO) will dry or cure much faster. You can use your nose, when the smell is gone then you can apply your finish coats. I have always had good luck using Formby's tung oil finish, a combination of oil and finish. Will dry over night. Light sanding between coats.

[Bill Wilson]

Trackman,

Mick is right. Oil is primarily a grain enhancer. Generally speaking, plain oil, whether it be tung oil, boiled linseed oil, lemon oil, mineral oil, etc make poor stand alone finishes. They have their place and in certain applications they are the best choice. Mineral oil is frequently used for food contact items. BLO has long been used on tool handles. However, for general woodwork, either as a decorative or protective finish, there are much better products out there.

I often use BLO to pop the grain on woods like walnut, mahogany & cherry. It imparts an amber tint that really enhances these darker woods. I can then apply any top coat I wish and get the particular benefits of that topcoat as well as the color enhancement of the BLO.

If I'm looking for a water clear finish to preserve the light color of woods like maple, then I wouldn't use BLO, but then again, I probably wouldn't use an oil varnish or danish oil either. I also use BLO as an ingredient in a home made danish oil recipe, equal parts BLO, mineral spirits and oil varnish.

So, oil has its place in finishing, but mainly as a complement or supplement to other products.

[Trackman]

I sure thank all of you for your help! I have went back to August in the posts about finishing. Someone (maybe it was you Bill) posted a good idea and that is to take a piece of scrap of the type you are using and try different things on it first.
Going to get some watco danish oil, tung oil, shellac, lacquer and any thing else that I may see an try them all and see what I like. Maybe get some 10w-30w an try that too, lol

[Bill Wilson]

Cardinal rule of finishing is to always do your experimentation on scrap of the same wood and prep as the project you are working on. That way you don't risk jeopardizing your project. Might I also suggest a couple of excellent books on finishing? Understanding Wood Finishing by Bob Flexner and Taunton's Complete Illustrated Guide to Finishing by Jeff Jewitt. These books have just about everything in them you could ever want to know about wood finishes. I highly recommend either one of them.