Given your son's asthma and allergies, I would recommend using a prefinished wood floor.
- These finishes are factory applied and have a consistency not possible with on-site finishing.
- They are very hard finishes with up to 25-year warranties for normal wear and tear.
- For the time that your son is living with you there is a good chance that the floor would not require refinishing.
- These finishes include metal oxide (one of the options you mentioned) and UV-cured acrylic urethanes, along with other polymers.
Any floor finish that you apply on-site is going to contain some VOCs and so will offgas heavily when applied, and then for some time after.
Also, a floor that is not prefinished will require sanding, and the dust from this is something that you will want to avoid.
Let's start with tung oil. It is made with pressed seeds from the nut of the tung tree and when applied to wood, penetrates deep into the grain, providing a tough, water-resistant finish.
It is a favorite of environmentalists as it is a natural, rapidly renewable resource, but as many natural resources do, it contains volatile organic compounds (VOCs).
Waterlox has a tung oil sealer, Waterlox 350, which has a VOC content of 350 g/L (grams/liter).
- As a reference, HUD allows a maximum of 400 g/L, whereas California, which is known for its stringent air quality requirements, allows a maximum of 275 g/L.
- Therefore, Waterlox would not be considered a low-VOC product and so might not be the best choice of tung oil, were you to use it.
- (See also "Is Waterlox considered a low-VOC product? After the initial application, is there anything in Waterlox that would offgas over time?" a Q&A answered by Florian Speier.)
I looked up Waterlox and read the MSDS (material safety data sheet). Under Section 3, Hazards Identification, it states, "may cause respiratory tract irritation if inhaled." This is further emphasized under Immediate Health Effects, where it states, "Mists of this material may cause respiratory irritation. Symptoms of respiratory irritation may include coughing and difficulty breathing."
I checked other tung oil MSDS's and found similar warnings.
Metal oxide floor finishes
For prefinished floors, you mentioned aluminum oxide, which is the most common of the metal oxide finishes.
- Metal oxide finishes are the hardest finishes available on the market.
- For the aluminum oxide finish, the metal oxide is mixed with a penetrating base and applied to the wood.
- The finish penetrates the upper layers of the wood, which not only enhances the grain, but resists scratching from normal use.
A metal oxide finish that is considered a safer choice is titanium dioxide (a material that is used widely in cosmetics and pigments).
Lauzon, a manufacturer based in Quebec, has a patented finish of "Polynium+ with Titanium Traffic" which is standard on all of its products.
Metal oxide finishes do not offgas or pose any health risk -- that is, until you refinish the floor and the dust is airborne during the sanding process. I read in one review that aluminum oxide dust is a proven lung irritant and may be a carcinogen. When I looked up their material safety data sheets, the products each have the same Hazard rating of 1, which is considered slight (0=least, 1=slight, 2=moderate, 3=high, 4=extreme).
Urethane floor finishes
If you are uncomfortable using the metal oxide finishes, there are several manufacturers that have prefinished flooring made with urethanes.
- EcoTimber, a reputable manufacturer located in California, offers engineered and solid wood floors finished with UV-cured acrylic urethane with a scratch-resistant topcoat.
- NordStar developed a polymer surface that is UV-cured, and an equally hard finish.
For more information:
Read our backgrounder "Selecting Healthy and Environmentally Sound Clear Wood Finishes" for pros and cons of many clear wood finishes.
Also, read "What is truly the healthiest wood floor option, and what are the safest finish products to use?" a Q&A answered by Victoria Schomer.