Aluminum oxide is an additive to water-based urethane finishes, while polyurethane is an old-school, oil-based finish that doesn't contain aluminum oxide. The application of either product has definite benefits, with some disadvantages. In some instances, the softer polyurethane is more appropriate than the glassy, hard surface offered by aluminum oxide urethane.
Urethane and polyurethane are sometimes confused with each other, because both products contain urethane. The differences are in the formulations between the two. When additives such as aluminum oxide are added to urethane, it becomes high-performance urethane, with different characteristics than polyurethane, or basic urethane.
Aluminum Oxide Explained
Aluminum oxide is a naturally occurring element, typically found in a crystal form, and used as an abrasive for sandpaper. When ground into a white powder, it's used as a filler ingredient for paints, plastics, sunscreen, and cosmetics. It's also used as a fortifier for urethane, imparting hardness and abrasion-resistant qualities lacking in polyurethane.
Polyurethane has additives that resemble the elasticity and physical properties of rubber or plastic. Polyurethane provides greater flexibility, but less wear resistance than aluminum oxide urethane. Polyurethane is available in two basic types, water and oil-based. For the sake of comparison, old-school, oil-based polyurethane is typically compared to water-based aluminum oxide urethane, because oil-based polyurethane performs better than water-based polyurethane.
Differences, in Layman Terms
Aside from the chemical differences between aluminum oxide and polyurethane, there are obvious differences in performance that have a direct effect on your floor.
Polyurethane ages to a warm, amber tint, bringing out the natural beauty and grain of a particular wood species. Aluminum oxide urethane dries clear, with minimal changes in color, enhancing grain patterns to a lesser extent. If you prize the old school appearance of golden hues and grain patterns, polyurethane is a better choice.
Glassy or Dull
Aluminum oxide urethane dries to a glassy shine. Polyurethane, even though shiny, dries with less sheen.
Polyurethane scratches can often be buffed out, and are not highly visible. The scratches in aluminum oxide show up with a whitish powdery look, and are harder to repair because of the hardness of the material.
Paws and Feet
Polyurethane finishes are softer than aluminum oxide urethane, and feel better on bare feet and paws, which makes them more appropriate for children and pets.
Re-coating and Refurbishing
Polyurethane finishes are easier to redo than aluminum oxide urethane, which typically requires a complete stripping before the addition of new coats.
Because aluminum oxide urethane is more durable than polyurethane, it's used more often commercially than polyurethane.
The majority of pre-finished, engineered wood has an aluminum oxide finish, with high-end grades almost always finished with aluminum oxide urethane. Polyurethane on engineered wood is not as common.
Residential on-site applications of polyurethane are more common than aluminum oxide urethane, partly because it's been the DIY choice for many years. It's more user-friendly and allows first-timers trying to refinish their own floors a better chance to get it right.