Wood Floor Refinishing and Moisture Cure Urethanes

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.

MCUs contain solvents and reactive chemicals that evaporate into the air and cause strong odors. Exposure to these chemicals can lead to health effects depending upon the level and duration of exposure.

Chemicals 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. VOCs can be harmful and are regulated by the New York State Department of Environmental Conservation (6 NYCRR Chapter III, Part 205).
    • It is not legal to sell or use wood coatings that have a total VOC level higher than 275 g/L in NYC. This includes ‘coating kits’ or repackaged bundles of multiple quart-sized containers. VOC levels must be printed on the MCU product 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 do not easily evaporate.

Vapor emission levels from using MCUs indoors vary depending on the amount of product used, surface area treated and ventilation.

Avoid Health Problems

Always consider using a safer and less volatile product than MCUs. If MCUs are being applied in your home, you should leave your home until the product fully hardens or “cures.” This may take 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 MCUs and you live in a multi-family building, ventilate common hallways and stairwells during application and curing to remove odors and vapors.

Brief exposures to elevated levels of MCU vapors can cause temporary irritation of the eyes, nose and throat and worsen asthma. Health effects may include headaches, nausea and dizziness.

Very high or long-term exposures can lead to more serious health effects. These may include organ damage, birth defects or pregnancy complications, chemical allergies and cancer.

After MCUs are applied, the liquid coating turns into a hardened surface. The hardened surface is not hazardous.

Choose a Safer Product

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. However, they should be used with care.
  • Oil-based products usually contain strong smelling solvents that may cause health concerns similar to MCUs. These products are subject to the same VOC limit (275 g/L) as 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.

More Information

  • Talk to your doctor if you or a family member has symptoms caused by exposure to chemicals.
  • Call 311 if you have additional questions about MCUs.
  • Call 311 or go to 311 online to report a chemical odor originating from within a building.
  • Call the New York State Department of Environmental Conservation (DEC) at (718) 482-4944 if you think that an MCU product is being used in violation of New York State Law.