A transparent urethane finish with no significant colour added to the wood.

I’ll be teaching you how to succeed with polyurethane (often called just “urethane” for short). Although there are different ways to apply polyurethane, in general it was easier to succeed with a polyurethane finish in the past than it is now. Government regulations have made water-based urethanes far more common and oil-based urethanes much less available. Overall, it’s easier to succeed with oil-based urethanes because they dry more slowly. That said, the methods I’ll teach you here will always deliver excellent results as long as you follow the steps properly. You’ll also increase your odds of success if you use the specific products that I know work well and recommend. I have no reason to recommend them except that they work best.

Creating a smooth, transparent finish on interior trim, doors, furniture and cabinets is easy when you complete the right steps, in the right order and in the right way. What you’ll discover here in this section is one approach I’ve been using to finish wood, simply and successfully for about 35 years. 

There’s one important step, no matter what type of finish you’re applying: surface preparation. It’s a critical step that sometimes takes more time and effort than the actual application of the urethane itself. 

Sidebar: Quick-Start Guide for The Basic Finish

This short guide will get you going fast if you already know something about wood finishing, and just need basic direction. For detailed directions, read on to the end of this section. 

Step 1: Sand wood surfaces so they’re smooth and scratch-free. 

Begin with an 80-grit abrasive if the wood is at all rough, progressing  incrementally through 120-, 150- then 180-grit. Don’t skip any steps.

Step 2: Clean the surface thoroughly with a vacuum.

Any kind of vacuum will do, but you do need a soft brush attachment on the hose. Hard plastic can damage the surface you’re cleaning. Some plastics can even leave behind black streaks.

Step 3: Apply the first coat of urethane.

Your wood will be thirsty at this stage and will soak up urethane quickly. Don’t over-coat. You’ll have opportunities later to build a protective layer. For now, just apply the urethane evenly with medium thickness and let it sit. Be sure to shine a strong light at a shallow angle on the surface so you can see where you’ve coated and where you’ve missed.

Step 4: Sand first coat with 240-grit paper after it has fully dried and vacuum the surface clean.

Your wood will feel rougher at this stage than before you coated it because the urethane caused surface fibers to swell and stand upright before hardening. Use 240-grit paper in a ¼-sheet finishing sander or by hand in the direction of the wood grain only. Be gentle, especially around corners. You don’t want to sand completely through your thin first coat, but you do need to remove all raised-grain roughness.

Step 5: Apply a second and third coat of urethane, sanding with 240-grit paper after the second coat, then vacuum clean.

This is the same procedure as the previous step, except that the wood won’t be nearly so thirsty. You probably only need a thin coat; a thick coat may run. Whenever possible, orient surfaces horizontally while coating and for a little while afterwards. Let this finish begin to harden to prevent runs when you rotate the item to coat another horizontal surface.

Three coats is a minimum. Sand with 240-grit paper and apply a fourth coat if you want even more protection, or you plan to buff the surface.

Optional Step 6: Power buff for a glass-smooth finish.

The process of buffing urethane finishes creates a flawless finish. All the details you need are coming up later in the course.