With a little practice, you can install floor trim like a pro. This column deals with the most common wall angle: 90 degrees.

The first rule of thumb about trim is that once you determine the angle of your corner, the two pieces of trim that are being cut should equal the whole angle. In other words, if you are cutting trim for a corner that is 90 degrees, both angles of the trim should be 45 degrees to equal 90. This sounds a bit elementary but this rule comes in handy for learning to fit angles at any degree. Any two pieces of trim should equal the total determined degree you are working with. If you have a wall that has a turn of only 60 degrees, you must cut miters to equal the whole (20-40=60, 30-30=60 etc). The two miters do not have to be each cut the exact same angle but must equal the total degree of the turn.

This rule is important because as you begin to install floor trim (or any type of trim), you will find that few walls are a perfect 90 degrees. You do not get a good fit on corners that are 91 degrees cutting two 45’s. Use a angle finder to determine the angle of the corner. Some corners (inside or outside) may be off as much as 5 degrees or more. If a corner IS 90 degrees then you know that cutting each piece of trim 45 degrees should fit well. If the corner is 88 degrees, then cutting each piece 44 degrees should give you a good fit (44 44 = 88). Remember the rule above to save a lot of headache and hit-miss cuts: The angles cut should equal the whole.

I have found that when working with 90 degree corners it’s ok to first cut one piece of the trim 45 degrees. Hold the piece of trim in position then use a piece of scrap (cut 45 degrees also) held against it. If you have a good fit, go ahead and cut the next piece 45 degrees to fit. If the fit is not tight then you know the corner is not a true 90 degrees. Use your angle finder to see what degree the corner is. If it is 90 1/2 degrees then you will know to cut you second piece 45 1/2 degrees (45 45 1/2 = 90 1/2). As you use this method, later with more experience you can “eye” how the second piece needs to be cut. For any problem angle, use trim scraps to determine the right cut first.

When cutting these pieces on the power compound miter saw, stand up the trim against the saw fence for a good cut and easy control. Laying the piece flat on the saw table is often hard to control and see your mark. Also the saw tends to work harder and could burn your piece. Before beginning a large project, spend a weekend practicing cutting miters both for outside and inside corners. See how you do by holding your cut pieces against corners of any wall. You will find that by adjusting angles just a little on your saw, you can make a very nice tight looking corner. Once you get the 90 degree angles down, moving on to other angles will be a lot easier!

Tip: When installing floor trim in a room that will have carpet installed, a space of about a half inch to 3/4 inch should be left under the trim to tuck in the carpet. Some people use spacers to hold the trim above the floor while nailing but instead you can simply hold your middle fingers under the trim while nailing which gives good spacing and saves time.