What's the difference between polyurethane and varnish?
Polyurethane is a durable, plastic-like resin finish known for its resistance to water, chemicals, and abrasion, making it ideal for high-traffic surfaces. Varnish, on the other hand, is a traditional finish made from oils, resins, and solvents, offering good protection and a natural look, often used for exterior applications or projects needing UV resistance and flexibility. The key difference lies in their chemical composition, flexibility, and resistance properties.
What is polyurethane? (composition, properties, best uses)
Polyurethane is a synthetic resin that forms a very hard, protective film over wood surfaces. It comes in both oil-based and water-based formulas, each with distinct characteristics. Oil-based polyurethane offers a slightly amber tint, dries slower, and is extremely durable, making it excellent for floors, countertops, and tabletops. Water-based polyurethane dries faster, is clearer, and has lower VOCs, suitable for furniture, cabinets, and other interior projects where a clear, non-yellowing finish is desired. Its primary properties include superior abrasion resistance, water repellency, and chemical resistance, making it a go-to for surfaces that see a lot of wear.
What is varnish? (composition, properties, best uses)
Varnish is a traditional clear finish made from a blend of drying oils (like tung or linseed oil), resins (natural or synthetic), and solvents. Unlike polyurethane, varnish is generally more flexible and less prone to chipping, especially over wood that expands and contracts. This flexibility, combined with good UV resistance, makes varnish an excellent choice for exterior wood surfaces like doors, window frames, and marine applications. Interior projects that benefit from varnish include fine furniture, antiques, and paneling where a natural, warm aesthetic and moderate protection are desired. While durable, it may not offer the same level of impact or chemical resistance as polyurethane.
| Feature | Polyurethane | Varnish |
|---|---|---|
| Composition | Synthetic plastic resin (oil or water-based) | Drying oils, resins (natural/synthetic), solvents |
| Durability | Very high abrasion, water, chemical resistance | Good UV resistance, flexible, moderate abrasion |
| Flexibility | Less flexible, can chip on moving wood | More flexible, handles wood movement better |
| Best Uses | Floors, countertops, high-traffic furniture | Exterior wood (doors, marine), fine furniture, antiques |
| Appearance | Clear (water-based) or amber tint (oil-based) | Warm, natural ambering over time |
| Drying Time | Faster (water-based), slower (oil-based) | Generally slower |
Which one is right for your project?
Choosing between polyurethane and varnish depends entirely on your project's specific needs and the environment it will be in. For interior surfaces that will see heavy use, like kitchen tables or hardwood floors, polyurethane's superior hardness and chemical resistance make it the clear winner. If you're working on an exterior project in Smiths Falls, such as a garden bench or an outdoor door, varnish offers the crucial UV protection and flexibility needed to withstand the elements without cracking. For delicate antique furniture or pieces where you want a very natural, hand-rubbed look, a traditional varnish might be preferred. Our staff, with years of combined experience, can walk you through the options. They've seen it all and can help you avoid common pitfalls when choosing the right finish.
Worried about picking the wrong finish? Our staff provide consultative guidance at the paint counter, helping homeowners select products and finishes. We'll help you get it right.
Common mistakes when choosing between them
One of the most frequent errors is using polyurethane on exterior wood. While it's tough, its rigidity means it doesn't flex well with wood's natural expansion and contraction due to temperature and humidity changes, leading to cracks and peeling outdoors. Conversely, using varnish on a high-traffic interior floor might not provide the abrasion resistance needed, resulting in premature wear. Another mistake is not considering the desired aesthetic; polyurethane can sometimes look more 'plastic-like,' while varnish typically offers a deeper, more traditional wood finish. Always consider the exposure to sunlight, moisture, and physical impact before making your choice.
Where to buy and what to ask at the store
When you're ready to select your wood finish, visiting a dedicated paint and decorating store like Falls Decor in Smiths Falls is your best bet. We carry a range of MF Paints products, including those suitable for wood finishing. We carry MF Paints, a 100% Canadian brand, developed and manufactured here since 1967. Don't be afraid to ask specific questions about your project: What type of wood is it? Is it indoors or outdoors? How much traffic or wear will it get? Do you prefer a satin, semi-gloss, or gloss finish? These details help our team guide you to the exact product you need, ensuring you leave with the right polyurethane or varnish for a successful project.
Will the staff judge me for not knowing what I'm doing? Absolutely not. Our staff are patient, non-judgmental, and happy to help clients of all experience levels.
The questions we get asked most.
Generally, it's not recommended to apply polyurethane directly over varnish without proper preparation. Varnish is often softer and more flexible than polyurethane, which can lead to adhesion issues and cracking. If you must, sand the varnished surface thoroughly to create a strong mechanical bond, then apply a test patch to ensure compatibility before committing to the entire project.
Water-based polyurethanes are typically the most resistant to yellowing, maintaining a clear finish over time. Oil-based polyurethanes and varnishes, especially those with alkyd resins, tend to amber or yellow with age, which can enhance the warmth of certain wood tones but might be undesirable on lighter woods or when a crystal-clear look is preferred.
Water-based polyurethane is often considered easier for serious DIYers due to faster drying times, lower odor, and easier cleanup with water. Oil-based polyurethane and varnish can be more challenging due to longer drying times, requiring good ventilation, and cleanup with mineral spirits. However, each has a learning curve, and technique plays a big role in a smooth finish.
While some varnishes are formulated for exterior use and offer good UV protection, they might not be the best choice for a high-traffic surface like a deck. Deck stains and sealers are often designed with better penetration and flexibility to handle the extreme weather and foot traffic a deck endures. Always check the product label for specific outdoor/deck recommendations.
Yes, light sanding between coats is generally recommended for both polyurethane and varnish. Use a fine-grit sandpaper (e.g., 220-320 grit) to gently scuff the surface, which creates microscopic scratches for the next coat to adhere to. This also helps smooth out any imperfections or dust nibs. Always wipe clean with a tack cloth before applying the next coat.