In Raiders of the Lost Ark, Dr. Jones uses a crystal-topped staff to focus a beam of sunlight on a scale model of ancient Tanis. As the sun moves, it eventually pinpoints the location of the lost Ark of the Covenant. The Staff of Ra—which looks a lot like a type of sundial called a noon mark—works because the sun’s path is predictable. I’ve always been fascinated by how sunlight could be harnessed so precisely. Sundials rely on the same principle as Indy’s staff: as the sun moves, a cast shadow shows what time it is. This project brings that ancient idea to the cottage, combining slipform stone masonry with cast concrete to make an enduring sundial.
In masonry, slipforming is a method of stone construction using a form— typically a box open on the top and bottom—that moves up as the structure is built. It’s ideal for beginner projects, since you can easily keep the structure plumb and level, even if your mortar work is a little sloppy and your stones are not perfectly positioned. Dressing the stones (adjusting their size and shape with various tools) is also unnecessary. Once mastered, this method can be scaled up to produce larger walls.
Start at the bottom
Like any good masonry project, this one needs a solid base. For a 12″ by 12″ column, dig a 12″ deep hole about 20″ in diameter. Compact the dirt at the bottom of the hole, and fill with 8″ of gravel. Top the gravel with 4″ of sand, compacted so it’s level with the surrounding grade. This may seem like overkill for such a small project, but a proper base helps water drain away from the column. Water trapped underneath the column can freeze and heave—sending the sundial tumbling.
Get your stones in a row
You need three components to make the column: the form, stones, and mortar. This slipform is simple to build. Cut ½” plywood panels and 2×2 braces to size, then fasten together with deck screws. Clamp or screw the panels together into a box, and centre and level it on the compacted base.
You can also coat the inner surface with vegetable oil (or seal it with varnish or paint). This acts as a release agent so the concrete doesn’t stick to the form. I don’t find a release agent necessary with such a small, easily dissembled form, but there’s no harm in using it if you like.
I’m lucky to have lots of small (3″ to 5″) diameter stones on my cottage property. But you can also get stones at a landscape supply yard. Either way, you’ll need about 30 to 50 per cent more than it takes to fill the column. That way, you can pick and choose for the best fit and appearance as you build. Regular mortar mix is fine for this project. You’ll have about 90 minutes of working time with the mortar, so mix a small amount at first to gauge how many stones you can comfortably set in that time. Start the stonework by laying a 2″ to 3″ bed of mortar at the base of the form.
Now place stones in a single layer, or course, around the inside perimeter of the form. As you do, examine each stone carefully to determine which face of the stone will look best exposed. Tuck the stones up tightly to the plywood form. Fill the space in the middle with less attractive stones, leaving gaps of about 1″ between each. Once the first course is placed, trowel some mortar overtop and work it between the stones— pushing it right up to the form. Hands are the best tools for this step, but wear rubber or nitrile gloves to protect from the caustic mortar. Finish the layer with a new bed of mortar on which to lay the next course of stones.
Repeat, course by course, until you get to the top of the form, then let it cure for 24 hours. Unscrew or unclamp the form to remove it, then reassemble it higher up the column, overlapping a course or two of stones below, enough to help stabilize the form. Since the form is no longer resting on the ground, screw some extra 2×2 braces on the corners, like chair legs, for support. Now, repeat the stone layering process until the column is as high as you like.
Illustration by Paul Lewis
Ace the base with slipforming or stonemasonry made easy
Illustration by Paul Lewis
Ace the base with slipforming or stonemasonry made easy
Illustration by Paul Lewis
Ace the base with slipforming or stonemasonry made easy
Noon marks
The most basic form of sundial, the noon mark, can be as simple as a rod poking south, out of a south-facing wall. When it’s precisely solar noon—the time when the sun is highest in the sky—mark the tip of the shadow on the wall and draw a vertical line. When the shadow hits that line, on any other day of the year, it’s also solar noon. Noon on modern clocks—“civil noon”—is not the same time as solar noon.
That’s mostly because the time zones we’ve invented mean we share the same civil noon over a zone that has a range of solar noons. But it’s easy to find when solar noon is happening: just search online for “solar noon today” and your cottage’s location.
Noon marks were added to historic buildings, often as a rod with a stylized sun on the end that casts a decorative shadow. They were used to calibrate mechanical clocks, back when civil noon and solar noon were the same—if you could see exactly when noon occurs, you could set your watch by it.
Cast the dial
For longevity, the sundial face is cast in concrete. The gnomon, the triangular piece, is metal. Like me, you probably have scrap metal bits that would work well with a bit of finishing. Or you can enlist the help of a local metal shop to fabricate what you need. There are even online services—readysetcut.ca and cutmyparts.ca are two—that will cut and dress custom metal shapes from a sketch or a digital file.
Why metal, not wood? Metal lasts longer no matter the weather, and, if it’s thick enough, will resist bending. Steel, stainless steel, brass, or copper can all work, depending on the look and patina you like. To cast the concrete top, build a square mould cut from ¾” melamine-surfaced particleboard. I use cheap white shelving for small concrete moulds like this. Cut the pieces according to the plan, and fasten with 1½” screws. Coarse-thread particle board screws work great here because they don’t require pilot holes and won’t deform the shape of the mould.
The markings on the surface of the sundial can be created in the mould before the concrete is poured or can be applied to the surface after casting. One way to add the markings to the mould is to use 100 per cent silicone caulk to draw the lines in the mould. You could also set small stones—maybe beach glass—in place, using a small dab of hot glue, to mark the hours.
But how do you know exactly where the lines should go? You can use complex math to compute angles and positions, or you can find an online calculator, like the one at blocklayer.com/sundial. With your cottage’s latitude, the diameter in millimetres of the sundial face, and the thickness of the gnomon, the calculator will produce a printable template. The gnomon itself can vary in size, as long as its angle matches your latitude.
Illustration by Paul Lewis
Face time: cast a sundial in concrete
Illustration by Paul Lewis
Face time: cast a sundial in concrete
This ain't your grandma's gnomon. Unless grandma’s cottage is on the same latitude as Paul’s place near Parry Sound, Ont. Sundial faces and gnomon angles are latitude-specific. To get a template for your cottage sundial, visit blocklayer.com/sundial.
Illustration by Paul Lewis
Face time: cast a sundial in concrete
Once the mould is ready, mix up some sand-mix concrete (no gravel; see “Solid Info on Bagged Mix,”) and fill the mould. Screed the top flat with a short length of 2×2 riding on the top edges of the mould. Tap the mould with a hammer as you go to help the concrete settle and release any air bubbles. Allow the sundial to cure for a few days before carefully removing the mould.
To complete the project, trowel a thin bed of mortar on the stone column and set the sundial on top. Point the gnomon to true north (not magnetic north) and level the surface. There’s no need to apply a finish on the project—concrete acquires a beautiful patina over time.
Georgian Bay cottager Paul Lewis wrote about building a French cleat wall storage system in the Sept/Oct ’24 issue.
This story originally appeared in our June/July ’25 issue.
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