The difference between water based and solvent based polyurethane

How many types of finish are out there?

Today, we can roughly divide the floor finishing products into three major groups.

• First, there are the surface finishes, which form a protective film on top of the wood - shellac, varnish or lacquer. 

• The second group consists of penetrating oils and sealers represented by the likes of linseed and tung oils. These products are popular in worktops restoration and furniture restoration.

• Third are the wax finishes, which are also penetrating and popular among those who prefer more natural solutions with low toxicity. These are popular in wooden flooring industry, as they are more durable and more suitable for traffic and require re-oiling / waxing service every couple of years.

What is polyurethane?

Polyurethane is a versatile polymer made from the chemical reaction between a diisocyanate and a polyol. It is known for its durability, flexibility, and resistance to abrasion and chemicals. Polyurethane is used in various forms, including flexible and rigid foams, coatings like floor lacquers, adhesives, elastomers, and thermoplastics, finding applications in furniture, insulation, automotive parts, footwear, and more.

Water-based and solvent-based polyurethane are two types of finishes commonly used for wood and other surfaces. Here are the primary differences between them:

Composition

• Water-Based Polyurethane: Uses water as the primary solvent, making it lower in VOCs (volatile organic compounds) and less odorous. It typically has a milky appearance in the can but dries clear.

• Solvent-Based Polyurethane: Uses organic solvents (like mineral spirits) as the primary solvent. This type has higher VOC content, resulting in a stronger odor during application. It usually appears clear or slightly amber in the can and dries to an amber hue.

Drying Time

• Water-Based Polyurethane: Dries faster, often within a few hours. Multiple coats can be applied in a single day.

• Solvent-Based Polyurethane: Takes longer to dry, often requiring 24 hours or more between coats.

Durability and Hardness

• Water-Based Polyurethane: Provides a durable finish that is resistant to scratches and wear, but generally not as hard as solvent-based polyurethane. It is also more flexible, which can be beneficial for certain applications.

• Solvent-Based Polyurethane: Known for its very hard and durable finish. It tends to be more resistant to heat and chemicals compared to water-based finishes.

Appearance

• Water-Based Polyurethane: Dries clear without adding color to the wood, preserving the natural look. It is often preferred for lighter woods and for applications where the natural color of the wood is desired.

• Solvent-Based Polyurethane: Adds a warm, amber tone to the wood, which can enhance the depth and richness of darker woods. This ambering effect can be desirable for certain aesthetics.

Application

• Water-Based Polyurethane: Easier to clean up with soap and water. It tends to be less flammable and less toxic, making it safer for indoor use and for users with sensitivity to fumes.

• Solvent-Based Polyurethane: Requires mineral spirits or other solvents for cleanup. It is more flammable and has stronger fumes, necessitating better ventilation during application.

Environmental Impact

• Water-Based Polyurethane: More environmentally friendly due to its lower VOC content. It complies better with environmental regulations.

• Solvent-Based Polyurethane: Has a higher environmental impact due to its higher VOC content. Some areas have restrictions on its use due to environmental regulations.

Cost

• Water-Based Polyurethane: Generally more expensive than solvent-based versions. However, this cost can be offset by its faster drying time and easier cleanup.

• Solvent-Based Polyurethane: Typically less expensive initially, but may require additional costs for proper ventilation and cleanup materials.

Summary

• Water-Based Polyurethane: Best for indoor applications, lighter woods, and when a clear, non-yellowing finish is desired. It is environmentally friendly and has a quicker drying time.

• Solvent-Based Polyurethane: Best for outdoor applications, darker woods, and when a hard, durable finish with an amber tone is desired. It has a longer drying time and a higher environmental impact.