Trimming a Houseful of Windows — Production Style -
Hot-melt glue is plenty strong for this application — it
takes a hammer and chisel to remove the fence when I'm done
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
Head and Sill Assembly
I spot-glued the parting bead in the grooved extension heads,
using a gauge block to determine the offsets (Figure 7). 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.
Figure 7.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 (B). The author "tacks" and squares the sill to the jamb
ends with two dots of hot-melt (C), then makes it permanent
with a pair of countersunk drywall screws (D).
Two-inch coarse-thread drywall screws completed the
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 (Figure 8). 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.
Figure 8.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 (top).
Cardboard hot-melt-glued to the biscuit joiner deflects chip
exhaust onto the floor (above).
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 (Figure
9). The biscuits thus maintained the precise reveal.
Figure 9.With a completed jamb assembly on the
bench, the author prepares to attach the side casings. Hot-melt
holds the biscuits in the slots (top) and the casing against
the side jambs' exterior face, automatically governing the
finish reveal (middle). 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
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 (Figure 10).
Figure 10.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.
I installed all the stand-alone units first, working
It's common to install extension jambs to window frames with
long screws or nails, but instead I used Excel Xpress (AmBel,
fast-setting polyurethane adhesive (Figure 11). 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.
Figure 11.Here, the author applies a bead of
fast-curing polyurethane glue to the edge of the extension
jambs for a mulled window unit (top). Bar clamps squeeze the
trim kit against the window jambs and plaster (bottom left).
The glue foams as it cures and the excess must be cut away
while still pliable (bottom right).
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
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.