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Floor Refinishing & Moisture Cure Urethanes

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floor Moisture Cure Urethanes (MCUs) are a type of polyurethane that is used to coat wood floors in homes. They make a very durable and scratch resistant finish and are often used on gymnasium and bowling alley floors.


Are MCUs dangerous to health?
MCUs contain solvents and reactive chemicals that evaporate into the air and cause strong odors. Brief exposures to elevated levels of MCU vapors can cause temporary irritation of the eyes, nose, and throat, worsen asthma, and cause health effects such as headaches, nausea, and dizziness.

Very high and/or long-term (e.g. lifetime) exposures can lead to more serious health effects such as organ damage, birth defects or pregnancy complications, chemical allergies, and, possibly, cancer.

How can I avoid health problems if my neighbor or I use MCU on wood floors?
First, you should always consider using a safer and less volatile product. If MCU is being applied in your home, it is recommended that you leave your home until the product fully cures (more than 48 hours) or until the odors subside. When you return to your home, open windows and doors to air out lingering odors. If your neighbor uses MCU and you live in a multi-family building, ventilate common hallways and stairwells during application and curing to remove odors and vapors.

What chemicals are in MCUs?
The specific chemicals in MCUs vary from brand to brand but they typically contain:

  • Xylene, Ethylbenzene, and Acetates: examples of volatile organic compounds (VOCs), which are solvents that evaporate at room temperature and are commonly found in MCUs. VOCs can be harmful and are regulated by New York State. Until 31 December 2004, the maximum level of total VOCs must be below 450 g/L. On 1 January 2005, the maximum level will drop to 350 g/L. The level of VOCs must be printed on the MCU can label. At present many MCU products exceed the legal limit for VOC concentration.
  • Toluene diisocyanate (TDI): reactive chemical that makes some vapors
  • Urethane polymers: reactive chemicals that are thick and don't easily evaporate

Has sampling been done by the NYC Health Department?
In response to community concerns, the New York City Department of Health and Mental Hygiene (DOHMH) performed limited sampling in a multi-family building while MCU was being used. Air samples were collected in common hallways and in an apartment where MCU was not used. DOHMH found that the levels of MCU chemicals in the air in the common hallways of the building were much higher than in the untreated apartment. The hallway levels detected could cause headaches, irritation of the eyes, nose, throat and lungs, and worsen asthma in some individuals. More severe health effects would not be expected.

It is important to note that these sampling results do not provide us with information about how long or at what levels these chemicals would continue to be present. Also, air levels at different buildings where MCUs are used will vary based on the amount of product used, surface area treated, and ventilation. For a complete copy of this report, see Environmental Investigation of Chemical Ingredients of Moisture Cure Urethanes Used as Wood Floor Coatings.

Will the finished product cause health problems?
After the MCU is applied, the curing process begins and the liquid coating is transformed into a hardened surface. The hardened surface is generally considered to be inert and non-hazardous. In addition to being used in coating surfaces, polyurethane products are commonly used in clothing, such as "spandex", foam products, packing materials, and cushions.

Are there safer polyurethanes that can be used to finish wood floors?
Common alternatives to MCUs include water-based polyurethanes and oil-based polyurethanes. These products also use chemical solvents that evaporate into the air.
  • Water-based polyurethanes usually produce fewer odors and may contain less toxic ingredients but should be used with care.
  • Oil-based products usually contain strong smelling solvents that may cause health concerns similar to MCUs. As with any chemical product, the manufacturer's instructions must be followed. Improving ventilation can help to reduce the levels of airborne chemicals regardless of the product used.

Who can I call if I have questions or if MCUs are causing a problem in my building?
If you have additional questions regarding MCUs, you can call 311 for more information. If you think that an MCU product is being used in violation of New York State Law, call DEC at (718) 482-4944.

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Last Updated: June 21, 2012