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Ideas from Ed: Sill-y me (Volume 5, Issue 7)

Sometimes working on an old house reminds me of fishing. You never know what you’ve caught (or found) until you get things out into the open. If you expect an old house to be built a certain way, you’re bound to be disappointed. Things may have been altered over the years, or perhaps never built properly in the first place.

This month, I tackled the task of replacing a badly rotted windowsill on a garage. I knew the wood was not pressure-treated, like today’s wood might be, but I was hoping that underneath it there would be some type of 2x4 construction that a new sill could be nailed to. Nope! This work would be slightly complicated since I could not access the interior of the garage at that window because of several “built-ins.”

Here’s the sill that’s the object of this project. I could almost literally crush it in my hands, probably from a combination of old-fashioned water damage (rot) and maybe even some termites or other insects.

My plan was to make a duplicate of the “visible” part of the sill, cut out the bad wood, attach the new piece, and caulk around the joints. The first step, then, was to take careful measurements and sketch things out. Here’s my drawing:

Sills should certainly have a slope so that water drains away. On the drawing, you can see I wrote that the sill is 15 degrees off of horizontal. To get that measurement, I used an “app” on my cell phone called “laser level” and took that reading directly.

I cut the replacement piece of wood to width and length, but because it needed to be 1 ¼” thick instead of the normal “2x” size of 1 ½”, I had to run it through my planer to get it to the proper thickness. I cut both long edges 15 degrees off of “square” so the piece would sit straight down in the space and have the proper slope.

I then drew the needed lines onto each end and cut them on a bandsaw.

I set the bandsaw table to 15 degrees, too, for the side-to-side cuts, and tipped the piece forward at roughly the same angle for the front-to-back cuts. Otherwise, a piece cut normally would have edges that would interfere with placement. I rounded the front edge with 2 quick passes of a hand plane.

I did all the above prep work prior to cutting out the old sill, being reasonably sure I’d be able to attach the new one in place somehow. I used a vibrating multi-tool with a combination wood/metal cutting blade, since I knew I would likely encounter a few nails. As I’ve said before, if you don’t own a tool like this, run to the store immediately and get one! It’s absolutely one of the handiest tools you’ll ever have, and it can do things no other tool can do.

I cut vertically down through the old wood, which was even more rotted than I had thought. The cutting went easily, and I did need to cut through 2 nails on each end. To my surprise, there was literally nothing beneath this sill!

The sill I made fit perfectly in place, but with nothing beneath it, I had to drill and countersink screws in each “ear” to hold it in place. I used 4” ceramic-coated screws. Those, or stainless or galvanized ones, must be used in pressure-treated lumber, because the treatment chemicals are corrosive to plain steel fasteners. I was reaching uncompromised wood with the screws, and was confident things would be properly secured.

Satisfied with things, I sealed the joints with a paintable caulk, filled several imperfections in the wood (as well as my screw holes) and slapped on a coat of paint/primer. I glazed the edge of the glass nearest to this work. When I get some time, I’ll scrape and strip the old window paint, re-glaze the rest of the glass, and final paint everything. The window should be good for many more years!

I hope all your projects go well. Thanks for reading, and happy restoring!


If you’d like to download a PDF of this “Ideas” column, click here:

Ideas from Ed 2022_July_sill-y me
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