Slate-gray Window Box

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The color of this elegant window box planter was created by mixing black pigment with the cement. Experiment by adding different colored pigments to the mix to create a unique work of art for your windowsill.

. TIME IT RIGHT This project involves more effort

than some others but is well worth it. Allow one day to construct the mold and cast the concrete, and 48 hours for the concrete to cure. Make under cover if raining and protect the curing concrete from freezing temperatures.

Size Matters

Concrete may crack without reinforcement if the edge width is too narrow for its size. Our box edges were 1in (2.5cm) wide; for boxes larger than the one in this project, include reinforcing mesh or rods in the construction. Melamine-faced particle board makes a good mold: its surface aids unmolding. Particle board or plywood must be sealed with 2-3 coats of shellac.

Adapt the size of the planter to suit your space but consider the weight of the concrete.

TOOLS & equipment

^in (1.5cm) or thinner melamine – coated particle board (see page 184) wooden batten tape measure & pen or pencil handsaw

PVA glue & clamps electric screwdriver & screws safety equipment: surgical or rubber gloves & face mask concrete mix of 4.25kg white or grey cement, 425g black pigment powder, 6.38kg silver sand,

6.38kg stone dust, and 2.125l water metric scales for weighing plastic buckets, bowls, & strainer measuring cup dishwashing liquid (optional) cork stoppers cooking oil & paintbrush trowel or metal scraper sheet of plastic wrap, large enough to enclose the mold metal file &/or sandpaper in various grades


Agapanthus dwarf varieties, such as ‘Peter Pan’ or ‘Blue Baby’

*3h "Project Steps


Calculate and measure the pieces for the outer mold to achieve your desired box size, remembering battens are attached on the outside. Internal dimensions for our box were 8 x 7.5 x 7.5in (46 x 19 x 19cm). Using a handsaw, cut the pieces accurately to size; or you could opt to get them machine cut at a building supply store.


Calculate the size of the inner mold to give a suitable width to base and sides of the box (see p.184), and cut pieces to size; ours measured 16 x 5% x 8Min (41 x 14 x 16.5cm). Note that battens are fixed to the inside and there is no base piece. When constructing the molds, first glue the batten to the boards with PVA glue, clamp together, and leave for one hour before screwing it all together.


Measure out the concrete mix, adapting the quantities listed in proportion to the size of your box (see also page 178). To color it, add pigment up to 10% of the weight of the cement; any more than 10% will weaken the structure. Sift together the cement and pigment to ensure even distribution of color. Mix in the remaining dry ingredients. Add water, erring on a solid mix, and a squirt of dishwashing liquid to aid plasticity, if you like.

4 Cut several corks for drainage holes to the correct depth, space evenly, and glue in place. Brush oil over the corks and base and sides. Build a base layer of concrete level with the tops of the corks. Use a trowel or scraper to spread, pack in, and smooth the concrete.


Once you have filled the mold, tap all around to help remove air bubbles and then smooth the top edge of the concrete with a trowel. Loosely cover the mold with a sheet of plastic and leave to harden on a level surface, out of direct sunlight, for 48 hours.

Make concrete containers in different sizes, shapes, and colors, and group together for a feature effect. Great for small spaces like the tops of walls, steps, shelves, and corners.


Create a changing display of plants for year-round interest. Partner permanent evergreen plants, such as ivy, which gore structure, with seasonal plants for interest at different times of the year Candles create an ambient nighttime display

Two Ways to

Updated: October 12, 2015 — 9:07 am