Polyurethane has several disadvantages despite its durability and popularity. First, during application, oil-based polyurethane releases high levels of volatile organic compounds and isocyanates that cause strong odor, headaches, nausea, and respiratory irritation, requiring respirators and excellent ventilation and making it unsafe to stay in the house for days. Second, oil-based polyurethane yellows over time and adds an amber tint, which is undesirable for light or white woods. Third, it is not ideal for outdoor use without UV additives, as it cracks and peels in sunlight. Fourth, it forms a plastic-like film that can look artificial and hide natural wood feel, unlike penetrating oils that feel more natural. Fifth, it is difficult to repair, as you cannot spot repair polyurethane easily, you often must sand the whole surface and recoat. Sixth, it is not food safe for cutting boards and can chip into food. Seventh, it is not environmentally friendly, made from petrochemicals, not biodegradable, and can contribute to microplastics. Eighth, water-based polyurethane, while low odor, is thinner, requires more coats, raises grain, and is more expensive. Finally, polyurethane can be slippery when wet and can be scratched, showing white marks.
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