Polyurethane vs. Acrylic Urethane Finish

Strength

• In general, polyester urethane (polyurethane) is stronger than acrylic and better resists chemicals, abrasions, stains and substances like liquor. More flexible than the stiffer acrylic, polyurethane resist chipping and movement stresses. New, more powerful acrylic urethanes on the industrial market resist abrasion and wear almost as well as polyurethane, but these have been slow to come to the general public and as of May 2010 were available only to professionals in the auto, flooring, construction and manufacturing industries.

Drying Time

• Polyurethane finishes take longer to dry than acrylic urethanes. Various brands of each type have different dry and cure times, but acrylic-based finishes set and cure more quickly. Some acrylic formulas dry to the touch in under 10 minutes. Faster drying speeds application dramatically, but can make water-based urethanes trickier to apply successfully.

Application

• Both polyurethane and acrylic urethane may be sprayed on. Brush application of two-part urethanes of either type requires a quick, practiced hand. Acrylic urethane, particularly, gels so quickly after being spread that after two or three brush strokes, you won't be able to continue working on a spot without leaving obvious brush marks. Acrylics must be sprayed on boat hulls and furniture where a smooth surface is essential. Polyurethanes are more forgiving when brushing or rolling. Both types require at least two thin coats to ensure adequate coverage.

Coating

• Polyurethanes typically cover more square footage per gallon than acrylic counterparts. Most polyurethanes are harder to buff to a shine than acrylic-based products, though newer polyester resins have made some polyurethanes easier to buff.

Adhesion

• The more flexibile polyurethanes adhere to surfaces better than acrylics, although both have problems with adhesion. Both are frequently applied over an epoxy primer or have epoxy formulas. Epoxy primers prime the surface and level out imperfections, bumps and ridges that high-gloss urethanes tend to highlight.

Cost

• Acrylic urethanes are more expensive than polyurethanes, more complicated to apply and easier to mess up. Two-part polyurethanes are more expensive than one-part varieties. Brands vary considerably in cost, durability and performance. Acrylic urethanes vary most widely from brand to brand, with some performing as well as polyurethanes and others not doing nearly as well.

Ultraviolet Light Resistance

• Polyurethane clear-coats tend to yellow over time when exposed to UV light--more so than acrylics. Ultraviolet light (UV) breaks down finishes and the surfaces beneath them. Expensive additives can help improve UV protection to underlying surfaces for both polyurethane and acrylic urethane coatings and a few high-end acrylic urethanes come with UV protectants included.