Tung Oil as Hardwood Floor Finish: My Experience (I)

1. Experiment of Tung oil on white oak wood sample

Before deciding on Tung oil finish, I first chose white oak as hardwood material. White oak has a few major advantages as flooring wood. It is native to North America and abundant. It is impermeable to water due to its cellular structure. That makes it a wood of choice for historical ships, such as US Constitution. Its wood contains high level of tannic acid which makes it naturally resistant to rot, much more than red oak and other common hardwood. Tannic acid is not something unusual. Green tea contains relatively high level of tannic acid as well. White oak is relatively hard with janka hardness measure of 1360, almost the same as bamboo[WhiteOakJanka]. That makes floor not easy to have dents and scratches from falling objects and every use.

After settling down on white oak, I went to local Woodcraft store and bought a 6” by 6” piece of white oak wood which is about 1” thick and some sanding paper. I also bought a quart of Tung oil from the same Woodcraft store.

My very first experience with Tung oil was using T-shirt material lint free cotton rag to apply pure Tung oil, undiluted, to half of the surface on one side of the white oak wood sample. The Tung oil smell is pleasant and pretty faint. Nothing pungent or strong that I can not take. Tung oil was applied in one coat and then put put inside a storage room to let it dry. The ventilation for that room was two windows but covered with blinds.

It takes a long and slow process for pure Tung oil to dry. Four days later, when I checked it again, the surface is still wet. When I pressed my finger against the oil surface, my finger still gets wet. It took about 2 weeks for it to almost dry out and one month to completely dry out.

2. Thinning

I was only able to find two retailers of Pure Tung oil, Woodcraft and Realmilkpaint.com. The prices are 55 and 46 USD per gallon respectively, before tax, shipping and handling[WoodCraftTungOil, RealmilkpaintTungOil] at the time of my purchase, July 2011. Woodcraft has a local store which I can go and get some on the same day. Realmilkpaint.com does not have local stores and I have to buy it online whose shipping usually takes 3 to 4 days to reach me.

Out of the few websites which contain information on how to use this product, Realmilkpaint also did the most detailed job. It states that for hardwood flooring, Tung oil must be thinned before application. A few other websites, such as woodworkdetails.com[WoodWorkDetailsTungOil] and Woodcraft store clerk only stressed thinning the first coat. Thinning in subsequent coats was optional or not recommended. But all of them emphasized that only using lint free cotton rag to apply the oil. Once thinner is used, choice of solvent becomes inevitable. Not sure which one to follow, I ordered a pint of Tung oil and its recommended citrus solvent just to try it out.

Pure Tung oil from realmilkpaint.com and woodcraft is virtually indistinguishable to me in term of color and smell. After mixing Tung oil and citrus solvent bought from realmilkpaint.com with ratio of 1:1, I found tung oil becomes much more fluid. Citrus solvent(D-limonene) flows almost as smooth as water at room temperature. Wearing a respiratory, I applied the thinned Tung oil twice to the other half of the side of wood sample I previously applied unthinned oil. The result is pretty different. Thinned oil sinks into the wood quickly and the wood surface dried within half one hour, while unthinned ones sits there for days. The color of wood immediately changed after applying thinned Tung oil and becomes reddish brown, a much deeper and richer color than that receiving unthinned oil.

One week later, I checked the surface again. The half with thinned oil is completely dried and only has faint smell of citrus solvent. Given the drying time and the color, I decided to use thinned oil on all my applications.

3. Application

A. Preparation

A complete list of items: Two bags of lint-free rag from Lowes, one lb each bag; shoe cover; nitrile gloves, CVS, two boxes or 80 in total, a paint quail to mix oil and thinner; a respirator(it requires P100 and is absolutely needed); a box of trash bags to hold trash; a long handle mop; a rectangular paint box;

The normal sanding is needed. After the sanding, the floors look like this:

To be Continued