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Trimming a Houseful of Windows — Production Style - Continued

Hot-melt glue is plenty strong for this application — it takes a hammer and chisel to remove the fence when I'm done with it.

After I'd bullnosed all the ends in one operation, I ran all the long edges. Working in this order cleans up any minor blowout that may have occurred in end milling.

Notching Sill Horns

My next step was to notch the sill horns.

I clamped a stop block to my table-saw fence and raised the blade all the way to minimize overcutting. Although I crosscut the waste pieces on my band saw, this could also be done on site with a table saw or chop box.

I notched the parting bead the same way; it's recessed in the extension head jamb but extends past the side casings on both sides.

Head and Sill Assembly

I spot-glued the parting bead in the grooved extension heads, using a gauge block to determine the offsets. Then, using a temporary spreader and parallel-jaw clamps to hold the sides the exact distance apart, I glued the sills to the bottom ends of the jambs.


A spot of hot-melt adhesive (A) at either end of the parting bead groove provides fast installation of the bead.


Which — like the sill — has horns. A wood stop-gauge sets an accurate casing overhang for the parting bead.


The author "tacks" and squares the sill to the jamb ends with two dots of hot-melt.


He then makes it permanent with a pair of countersunk drywall screws.

Two-inch coarse-thread drywall screws completed the connection.

At this point, I had an actual fixed distance between the parting bead and sill horns. I checked it against my layout stick, made adjustments where needed, then cut all the side casings to length.

Adding the Casing

There was a 1/8-inch finish reveal between the casing and the edge of the extension jamb in this house. Over time, I've developed a technique involving wood biscuits to quickly maintain an even reveal, and I used that technique here.

First, I hot-glued a temporary backer square to my tabletop with a series of 12-inch-on-center reference marks penciled along its top edge. Then I set my biscuit joiner to cut a groove 5/8 inch down from the edge of the casing stock. I stacked the casings on edge, backside out, six at a time, in front of the backer, and I slotted each piece, following the reference marks for consistency.


The author uses wood joining biscuits to govern his casing reveals. The backing fence against which the stock is being pressed is hot-melt-glued to the workbench and has center marks along its top edge to guide the biscuit joiner. Stock stacked five deep in front of the fence receives a series of slots in a single, repetitive operation.


Cardboard hot-melt-glued to the biscuit joiner deflects chip exhaust onto the floor.

With all the casings slotted, I laid out the assembled jamb sets faceup on the table. I glued biscuits into the slots, then hit the exposed face of the biscuits with a dot of hot glue and pressed them against the outside of the extension jambs. The biscuits thus maintained the precise reveal.


With a completed jamb assembly on the bench, the author prepares to attach the side casings. Hot-melt holds the biscuits in the slots.


The casing against the side jambs' exterior face, automatically governing the finish reveal.


Finish nails complete the assembly.

The glue held things together while I shot 2-inch finish nails to permanently fix the casings.

I then screwed the parting beads and sills into the casing ends, using 1 5/8-inch and 2 1/2-inch screws respectively.

This completed the in-shop assembly.

Filling the Fillets

Because the head casings and sill aprons were relief-ploughed to account for plaster irregularities, the back-relief would be visible on the ends. So I used a glue-in fillet to give the installed ends a finished appearance.

I cut and planed the fillet stock to the exact width and depth of the plough, then chopped it into 1-inch lengths. With a stack of casings lying facedown with staggered ends, I applied a bead of HiPur and pressed the fillets down flush with a block of wood.


Fillets hide the gaps at head casing and apron ends. The author uses a block of wood to press the fillets down flush in a bead of hot-melt glue.

I left the fillets slightly proud of the ends, belt-sanded them flush, then wiped spackle into the end grain to fill the pores. I finished by touch-sanding with a 120-grit sanding block, which provided a smooth surface for painting.

For ease of transport and installation, I left the heads and aprons loose. I also left the common side casings off any units to be ganged on site; they would require custom fitting, best done in place.

Site Installation

I installed all the stand-alone units first, working alone.

It's common to install extension jambs to window frames with long screws or nails, but instead I used Excel Xpress (AmBel, 800/779-3935,, a fast-setting polyurethane adhesive. It has an open time of about five minutes and sets in 30 minutes or so. Using this adhesive eliminates the need for fasteners, which really speeds up installation.


Here, the author applies a bead of fast-curing polyurethane glue to the edge of the extension jambs for a mulled window unit.


Bar clamps squeeze the trim kit against the window jambs and plaster.


The glue foams as it cures and the excess must be cut away while still pliable.

Excess glue foams out of the joints as it cures, and this needs to be removed within about 15 minutes, while the adhesive is still relatively soft. Otherwise, it has to be chiseled off, and that's a chore.

To install the trim kits, all I needed was a good supply of bar clamps. I opened the window and added clamps to close the joint; not much clamping force was needed to draw the joints tight. I used gun nails at the top and bottom of the casings, just to hold the frames in alignment. This took took me about 10 minutes per window.

I finished up with hand nails, since they really draw the casing up tight to the plaster. But I waited until the glue had set to do the hand nailing; the clamping force was light, and hammering can shake the clamps loose.

The remainder of the trim packages — either mulled units or corner units — required some on-site assembly and another set of hands to make installation go smoothly.

In preparation, I went around and fit all the combination sills.

To support the sill stock during fitting, I hot-melt-glued temporary 2-by supports to the plaster below the windows. Once I had all the loose sills in the house cut and labeled, I glued and screwed them to their respective ganged jamb sets.

The combination trim kits were then ready to be installed using the same procedure I'd used for single units.

I wrapped up the job by installing the mulled-unit parting beads, head casings, and aprons. I brought my bullnose routers to the site to do all the extension touch-ups.

Mike Randruns a specialty millwork shop for Baud Builders in Narragansett, R.I.