Canadian Woodworking

Trim frames

Author: Steve Maxwell
Photos: Steve Maxwell
Published: February March 2010

A woodworker’s unique approach to making and installing door and window trim.


As a woodworker you have the chance to make and install better door and window trim than you’ll find in most homes, but you probably don’t realize the extent of your advantage. I’m not talking about simply reproducing the kind of standard trim profiles you’ll find in building supply outlets everywhere (though this a great idea), but rather a whole new way of milling, joining and installing trim that looks better, goes up faster and resists joint gaps much more reliably than usual. I call it the trim frame approach, and it all begins by redefining the way you think about this work and the traditional piece-by-piece installation process.

If you’ve ever installed door and window trim before, you’ve probably learned to hate the imprecise surface of drywall. Since it conforms to underlying irregularities in wall frames, drywall rarely offers a perfectly flat surface to support trim. This means that every piece of trim needs a certain amount of custom cutting to get angles tight, especially if you’re dealing with stained trim that doesn’t allow the use of filler.

Either the opening you’re trimming isn’t square (which means that you can’t simply cut 90º corners) or the drywall is crowned or dished enough that it throws joints out of kilter front-to-back. Sure, you can thrash around with a Surform plane to level out wonky drywall, and tweak your chop saw half a degree one way or the other to finesse an 89º corner joint tight, but why bother? It all takes too much time, and even if you do get the parts meeting perfectly, how long will they stay that way? A little settling and little shrinking, and all your futzing around is worthless as trim joints open up.

Simple solution
 Even with more complicated shapes to trim, this method makes quick work of trimming a door.

Easy yet elegant
 This relatively simple profile will make your doors and windows look great.

Take control
 The beauty of making your own trim is that you have ultimate control of the outcome of your work.

The Trim Frame Concept

Instead of all this trouble, consider the advantages of pre-joining door and window trim permanently into three- or four-sided frames ahead of time, then fastening these frames onto the wall as a single unit. This eliminates any and every hassle caused by wavy drywall and out of square openings, while also allowing you to create absolutely tight and permanent corner joints in the controlled conditions of your shop using biscuits, glue and clamps. The only thing that stands between you and these obvious advantages is an approach to trim design that lends itself well to biscuit joined corners.

What’s the easiest kind of corner to join with biscuits? Butt joints connecting flat pieces of wood. Trouble is, plain, butt-joined trim like this doesn’t look fancy enough for most situations. You need more, and that’s where something called layering comes in. Years ago, when all trim was milled by hand using moulding planes, cabinetmakers fashioned wide, lavish trim installations by layering smaller profiles piece-by-piece around a central frame. This same approach makes perfect sense with the modern biscuit-joined frame we’re talking about here. Start with a plain, pre-joined frame made of flat stock, then add your own shopmilled bullnose, cove or ogee profiles around the inside and outside edges to create as lavish a look as you like. It’s a custom process that can yield astonishing results.

Making Trim Frames Happen

Start by taking careful measurements of the inside dimensions of the door and window frames you’re trimming out, accurate down to 1/32″. These numbers will be quite consistent from one frame to the next if you’re dealing with modern windows and doors, yet may be surprisingly different if you’re working on an older home.

Either way, accuracy matters, though you don’t have to go crazy making allowances for door or window openings that aren’t quite square. As long as they’re accurate to within about ⅛” over their length, then you don’t need to custom cut corner angles.

Trim frames work best when they’re sized to include a piece of moulding on both the outside edges of the frame and the inside edges, added after the frame is fastened to the wall. Now’s the time to make decisions about what size these additional trim elements will be because these specs determine the overall outside and inside trim frame dimensions. Aim for a 3/16″ to ¼”-wide exposure of the door or window jamb (called a “reveal” in the trade) before the inner edge of the trim frame begins.

Cut vertical and horizontal trim frame elements, test-fit them together to double-check for correct size against the appropriate doors and windows, then cut and join as many frames as you need. Got some door trim frames as part of your project? Since they’ll only have three sides, use hammer-driven finishing nails to temporarily fasten a piece of wood across the back face of the bottom edge of the door frame. This lends support to what would otherwise be a hopelessly fragile assembly. Leave this brace on until moments before the trim frame is applied around the door.

The nice thing about using flat stock for the main body of your trim frame is that the face can be sanded smooth and flat. Level up all joints after the glue has dried, then mill all the additional trim profiles you’ll be adding to the frame during installation later. Need some ideas?

A classic approach involves a ½” to 1″-wide bullnose profile capping the outside edge of the trim frame, flanked by cove moulding to cover the joint, with smaller bullnose capping the inside edge. You might also consider routing two or three flutes down the middle of vertical frame members, to add visual details. You’ll also find that Roman ogee and round-over profiles work well milled into thin strips that form the layered trim elements.

When everything has been milled and assembled, it’s time to think about finishing. Now’s the best time to apply primer (if you’re completing a painted installation), or a stain and urethane finish if that’s your plan.

When it comes time to install trim frames, you’ll see firsthand why it makes so much sense. Trim goes up fast, with joints that are as tight and as permanent as you made them in the shop. Use a little glue and some pin nails to fasten the layer trim elements onto the frame and you’ll have a completed installation that boasts classic good looks for the long haul.

Fudge Factor

It’s not unusual for edges of door and window frames to not extend quite far enough out to meet the surface of surrounding drywall. This is a real pain because it means that part of the ugly edge of the drywall remains visible after the trim goes on. Unless you do something about it first, that is.

Instead of the huge and messy hassle involved in removing excess drywall or building up additional lengths of wood on the edge of the door or window frame, add a decorative strip to the inside edge of the trim frame, as part of the deal. Some ¼” or ⅜” diameter bullnose trim works perfectly here. It caps the edge of the trim frame, while extending down to meet flush with the face of the not-quite-long-enough door or window frame.

Biscuit-Joining Milled Profiles

Got your heart set on using a fancy profile that requires mitred corners? This doesn’t mean you need to abandon the trim frame approach. All you need is to switch strategies.

Although you could try and sink biscuit slots into mating faces of a mitred trim joint, this probably won’t work when it comes to profiled trim. The reason is precision. Unless your biscuit slots are aligned absolutely perfectly, the two profiles won’t mesh flawlessly on the surface. And since you’re dealing with various curves and undulations, you can’t expect to sand everything flush and have it look good. That said, there’s another way. Instead of starting the process with biscuit slots, end with them.

Use glue and clamps to join your profiled door and window trim into a frame without biscuits. Aligning the profiles perfectly is much easier since you’re not restricted in any way by a biscuit. After the glue has dried completely, gently flip the frame over (be careful, it’s not very strong yet), then plunge biscuit slots across the back face of each joint, at 90º to the joint line. Set your biscuit joiner for a deeper-than-normal slot depth, though not so deep that it comes through the face of the trim. Saw two, three or four slots across each joint (depending on the width of trim you’re using). Swab glue into the slots and onto the biscuits, then push the biscuits home. Let the glue dry completely, then saw and belt-sand protruding biscuits flush with the back face of the trim frame. Finish your wood, then install.

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