Interior Trim Work Basics

All the trim basics-start to finish-plus a clever way to get those miters tight

We show you how to make crisp, sharp corners and tight joints when installing door trim, window trim and a three-piece baseboard. With a few basic carpentry tools and a little patience, you can trim out a room in a weekend. With a little practice you can master the two key trim techniques, mitering and coping.

By the DIY experts of The Family Handyman Magazine

TIME

Weekend

COMPLEXITY

Moderate

COST

$100 - $500

Gather your tools and materials

In this article we'll show you the basic steps for installing a wide trim around a door and window, complete with mitered corners. We'll also show you how to put in a built-up baseboard made from a combination of three types of moldings.

You'll need several key tools to do a first class job. Use a power miter SAW for clean angle cuts. A power miter saw (Photo 2) vastly simplifies the job because it allows you to make incredibly accurate cuts in a matter of seconds. Even professionals admit they couldn't do the same quality of work without one. If you don't have a power miter saw, you can rent one.

TIP: If you're renting a miter saw, cut several scrap pieces to get the feel of the tool before cutting your trim.

Buy a good-quality blade for your miter saw. The more teeth a blade has, the crisper the cut. Choose a blade with a minimum of 40 teeth, although I prefer a blade with 80 teeth. It leaves a cut that's as smooth as glass, making it well worth the investment.

You'll also need a coping saw. This saw (Photo 18) has a narrow blade and tiny teeth that allow you to cut tight curves; it's available at any hardware store.

TIP: Avoid that annoying trip to the hardware store in the middle of your project—pick up a couple of spare blades in case you break one.

The only other tools you'll need are basic carpentry tools: a sharp pencil, a tape measure and a combination square. A wood file also is a must for fine-tuning joints (Photo 20). Use a round file, called a rattail file, for fitting tight curved profiles, and a combination flat/half round for all other trim (Photo 19). In this project, we predrilled our nail holes. If you have more than one room to trim, consider using an air-powered finish nailer to speed up the process.

If sawdust isn't a problem, cut your trim in the room where you plan to install it (Photo). This will reduce legwork and save a lot of time. Set up the miter saw in the middle of the floor with plenty of room on either side. Cover the floor with a tarp to prevent scuff marks and scratches. Use blocks the same height as the miter saw table to support long lengths of trim.

Prefinishing saves a ton of time

Once you get your trim home, sand and stain or paint the trim before you install it. To be perfectly honest, this part of the project isn't much fun. But it's a lot easier to finish trim before installation, working on sawhorses, than afterward, lying on the floor with sandpaper and a staining rag. Plus you can do a better job of sanding and finishing the pieces. After you've installed the pieces, be prepared to touch them up a bit. Do all the finish work in a well-ventilated area.

We applied a Salem maple stain to our trim and three coats of low-sheen varnish to protect it. Dispose of any staining rags carefully to avoid spontaneous combustion: Open up the oil-soaked rags and hang them up until they're completely dry. Then dispose of them in the trash.

Figure A: Trim Terms

Technical terms can be confusing. Here's a guide to trim carpenter lingo

Figure A: Trim terms
CAUTION

A miter saw is powerful and loud. Be sure to keep your hands well away from the blade and wear hearing protection and safety glasses when using it.

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Video: How to Trim a Door

Travis Larson, senior editor at The Family Handyman, will show you how to trim a door in about 10 minutes per side. The first time you do it, it will take a longer but once you get the hang of it, you'll be trimming out doors like a pro. If you are already a pro, you can still pick up some tips.

 

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Project 1: Case a door
Step 1: Fit one side casing

Start with the casing around the doors and windows. The first few times you install casing, we suggest drawing light lines (called “reveal lines”) 3/16 in. from the edge of the jamb to align the casing to the door jamb and windows (Photo 1). With experience, you'll skip this step and simply “eyeball” the reveal when you put up the trim.

Check the miters at the corners with two 12-in. sections of casing cut at exactly 45 degrees (Photo 3). Even though the corners should be a perfect 90 degrees, often they're not. In addition, if the jamb sticks out or is set back slightly from the wall, a 45-degree miter cut won't fit tight. By holding the test pieces at the corner you can see exactly how your casings will fit. If you see a gap, adjust the saw slightly and cut both pieces at the new angle (Photo 3).

TIP: Make small adjustments. Even one-quarter of a degree makes a big difference.

If the angle of the miter is accurate but a gap still appears along the face, the pieces are probably tipping back against the wall. Cut or file the backside of the miter (back cut). This allows the joint to fit tight on the face of the miter. Don't worry about taking too much off the back; it won't be visible. Mark and cut the first side casing at the angle you established with your test pieces (Photo 4). Always cut the pieces a little long and check the fit; the power miter saw gives you the ability to cut very slight amounts off with a high degree of accuracy. When the inside angle of the miter lines up with the reveal mark on the top of the jamb, tack the casing in place.

Don't split that perfect miter—predrill nail holes. With maple, oak and other dense wood, predrilling your nail holes in the casing is a must (Photo 5). Even with a softwood like pine, I prefer to predrill to avoid splitting a perfectly fit piece. Use a 1/16-in. bit for 4d nails, 3/32-in. for 6d nails and 1/8-in. for 8d nails.

TIP: Use a nail with the head snipped off as a substitute for a drill bit. The same size nail you're driving works best.

Tack the casing into the jamb first, then to the wall. Wait until you've fit all the casings before you drive the nails in completely in case something doesn't fit right and you have to remove the trim to recut it. We used 4d nails for the jamb and 6d nails for walls. If you're using thicker casing, increase your nail size one increment, using 6d nails in the jamb and 8d nails in he wall. Your nails should penetrate the studs and the jamb at least 3/4 in.

TIP On wood with a strong grain pattern, place your nails in the dark portion of the grain to make them less noticeable.

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Project 1: Case a door
Step 2: Install the top and second side

With your first corner fit perfectly, set the top casing aside and check the second corner with your test pieces the same way you did the first. Once you have established the angle of the miter, hold your top casing in place and transfer the reveal mark from the side jamb to your top casing (Photo 6). Cut the miter, check your fit and tack in place.

TIP: Match your pieces of wood so the grain pattern and color are similar at the joints.

Then mark and cut the second side casing, leaving an extra 1/32 in. for fitting purposes (Photo 7). Slide the casing into place parallel to your reveal marks and check your fit. If the miter is tight and the length is a little long, trim a hair off the bottom at a 90-degree angle until you get a perfect fit.

When your miters fit perfectly, “pin” the corners (Photos 8 and 9) to help align the two casings and keep the joint tight. Use your finger to press the casings flush with each other. You may have to slip a small shim behind one of the casings to align them. Next predrill the corners for 3d finishing nails, one from the top and one from the side (Photo 8). If your casing is less than 1/2 in. thick, you'll have to predrill the corners before tacking the casing up. Finally, work around the door, driving the nailheads slightly below the surface with a hammer and a nail set (Photo 10). Nail sets are sold in various sizes; choose one that matches the size of the nailhead you're using. Set the nails deep enough to hold nail putty: A good rule of thumb is half the diameter of the nailhead.

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Project 2: Case a window

There are two basic ways to trim a window. One way is to “picture frame” the window, so that all four corners are mitered to 90 degrees. This method is common on most newer homes, especially with casement windows. The second way is to install a stool and apron. Basically, this is a small ledge (a stool) at the bottom of the window with a piece of casing (an apron) under it. This method is normally found in older homes and is more often used on double-hung windows.

Trim a window using the same techniques as with a door. Mark your reveal lines, use test pieces to check your corners, and transfer the reveal lines to the casings for cutting and nailing. When you “picture frame” a window, however, install the top casing first (Photo 11), then the two sides, and finally, the bottom. Fitting the bottom is the toughest part, because you have to fit both corners at once (Photo 12). But if you use your test pieces and always cut the casing a little long, you shouldn't have any problem. Cutting the piece long allows you to adjust the miters if you have to. Once the miters are tight, gradually trim a small amount off with your miter saw until you have the proper length.

Trim out a window with a stool in the same order as you would a door, but with a few added steps. Install the stool first, then one side, the top and the other side. Install the apron under the stool last.

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Project 3: Install baseboard
Step 1: Nail up the large base

Begin by using a stud finder to locate the studs, and mark their location on the wall with a narrow piece of painter's tape (Photo 13). You can pull the tape off without leaving a mark. Rough-cut the baseboard about 2 in. overlong and lay the pieces along the wall. Install the longest section first and work away from the ends until you reach an opening or door. This ensures that the last cut will be a simple 90-degree cut.

In general, measure and cut each piece about 1/16 in. overlong to ensure a tight fit. If you don't have a piece of baseboard long enough to cover the entire wall, splice two pieces with a “scarf joint” (see Close-up of photo13). Bow the casing slightly to fit between the walls and press it into place. This ensures a nice, tight fit. But don't force the piece in. Trim a bit off and try the fit again. Continue around the room butting the inside corners at 90 degrees. When you come to an outside corner, use test pieces to find exact angles (Photo 14).

TIP: If you're adding a base cap, as we are, overcut the miter slightly, leaving the backside slightly open (Photo 16). The front side will be tight and the cap will cover the gap.

Nail the pieces in place using 6d finishing nails. You can also put a small amount of glue at the miters and cross-nail them with 4d finishing nails. But remember to predrill to avoid splitting the ends (Photo 16).

Corner Fitting Trick

If the drywall tapers in at the bottom of the wall or stops short of the floor, simply drive a screw at the bottom of the wall and turn it in until the head of the screw is at the same plane as the main wall. The head will prevent the baseboard from tipping in.

Support trim with screw
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Project 3: Install baseboard
Step 2: Nail the cap and shoe

Install the base cap pieces in the same order as the baseboard. However, because base cap has a curved profile, you can't butt the inside corners. Instead, make a “coped joint” by cutting off one piece square and cutting the adjoining piece to match the profile of the molding (Photo 19). Just follow the steps in Photos 17 – 20 and you'll find it's easier than it looks. (Actually, coping is kind of fun once you get the hang of it.) Practice a few times on scrap pieces to get used to it.

Install the base shoe last. Base shoe is usually used on hard-surface floors to conceal any irregularities or gaps between the floor and the baseboard. Even if your baseboards fit perfectly tight to the floor, you can install the shoe to add another dimension to your trim. Install the shoe the same as the cap, mitering outside corners and coping inside corners (Photo 21). Be sure to nail the shoe into the baseboard, not the floor, so it won't pull away from the baseboard when the flooring expands and contracts. Finally, set all your nails and fill them with putty. We couldn't find a putty color to exactly match the stain we chose, so we mixed two shades together (Photo 22).

TIP: With light-colored wood, always mix the color on the light side; darker putty stands out.

How to Shop for Trim

Stock trim is available in a wide range of styles from most lumberyards and home centers. We chose a relatively wide (3-1/4 in.) beaded casing to go around our doors and windows. It's 11/16 in. thick. We used three components to create the base: a 1/2-in. x 3-1/4 in. “hook strip,” a 9/16-in. x 1-3/8 in. base cap, and a 7/16-in. x 3/4-in. base shoe (see “Trim Terms,” above). Combine other standard trim types to create wider and more detailed shapes.

If you don't find a trim style you like or you're trying to match a molding in an older house, look in the Yellow Pages under “Millwork.” Millwork shops can custom-produce almost any type of trim from most species of wood. Custom work, however, comes at a price; be prepared to pay as much as three times the cost of stock moldings, plus setup charges. In addition, you may have to wait four to eight weeks.

Most trim is made of solid wood or medium density fiberboard with a wood veneer. Oak, pine, birch, maple and poplar are the most common types available. We chose maple for our project.

Sometimes you can find trim made of various types of plastic, most often prefinished in white, brown or simulated wood. This trim is far more stable than wood but cuts much the same, if not easier. What it lacks, however, is the warmth and varied grain pattern you can only find in real wood.

Purchase your trim in lengths long enough to cover each wall. If you can't purchase the trim in long enough lengths, don't worry. In the Close-up of Photo 13 above we show you how to splice two pieces to cover the length of a long wall.

Stock trim is available in a wide range of styles from most lumberyards and home centers. We chose a relatively wide (3-1/4 in.) beaded casing to go around our doors and windows. It's 11/16 in. thick. We used three components to create the base: a 1/2-in. x 3-1/4 in. “hook strip,” a 9/16-in. x 1-3/8 in. base cap, and a 7/16-in. x 3/4-in. base shoe (see “Trim Terms,” above). Combine other standard trim types to create wider and more detailed shapes.

If you don't find a trim style you like or you're trying to match a molding in an older house, look in the Yellow Pages under “Millwork.” Millwork shops can custom-produce almost any type of trim from most species of wood. Custom work, however, comes at a price; be prepared to pay as much as three times the cost of stock moldings, plus setup charges. In addition, you may have to wait four to eight weeks.

Most trim is made of solid wood or medium density fiberboard with a wood veneer. Oak, pine, birch, maple and poplar are the most common types available. We chose maple for our project.

Sometimes you can find trim made of various types of plastic, most often prefinished in white, brown or simulated wood. This trim is far more stable than wood but cuts much the same, if not easier. What it lacks, however, is the warmth and varied grain pattern you can only find in real wood.

Purchase your trim in lengths long enough to cover each wall. If you can't purchase the trim in long enough lengths, don't worry. In the Close-up of Photo 13 above we show you how to splice two pieces to cover the length of a long wall.

Trim adds style to a room
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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Hammer
  • Miter saw
  • Coping saw
  • 4-in-1 screwdriver
  • Drill/driver, cordless
  • Combination square
  • Nail set
  • Drill bit set
  • File
  • Glue
  • Putty knife

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Wood trim
  • Wood putty
  • Finish nails, 3d, 4d, 6d, 8d