Thin High-Strength Concrete Garden Bed Molds

Dress the Cured Concrete Castings

After curing, I take them outside to sand down any sharp edges left from the mold. And I’ll use a rub brick for this. It only takes a minute or two per casting. The rub brick is made from silicone carbide and it’s perfect for rounding and smoothing these edges.

thin concrete garden panel casting lined up — A close up of the thin castings showing a sharp edge left from the mold

Sanding concrete with a rub brick — Using the rub brick to smooth the edges on this 24″ thin concrete garden panel

Weight Reduction of Going Thin

After I’ll weight the castings to compare them to my original 2-1/2″ thick ones. The 24″ thin panels averaged 22 pounds and were 33 percent lighter.

The 36″ ones averaged 34 pounds and were about the same at 32 percent lighter.

weighing cast concrete panels on a digital scale — The 24″ thin panels weigh, on average, 22 pounds

weighing cast concrete panels on a digital scale — The thin 24″ panels are on average 33% lighter than my original ones

weighing cast concrete panels on a digital scale — The 36″ thin panels weigh, on average, 34 pounds

weighing cast concrete panels on a digital scale — The thin 36″ panels are on average 32% lighter than my original ones

Assemble the Raised Beds

To make a raised bed from these panels I use a spirit level, framing square, rubber mallet, and galvanized landscape spikes.

Tools to assemble the thin panel concrete garden bed

A Square 36″ Thin Concrete Raised Garden Bed

For this demo I’ll quickly put together a 36″ by 36″ square bed.
This spot was fairly level so I put it together over the wood chips between some existing beds.

a man assembling cast concrete panels to make a raised bed in the garden — Using a spirit level on the first panel of the raised bed assembly

a man assembling cast concrete panels to make a raised bed in the garden — Using a framing square to check the first corner of the box

a man assembling cast concrete panels to make a raised bed in the garden — Bringing in the side wall 36″ thin concrete panel

It’s good practice to ensure the panels are level and well supported on a layer of sand or fine gravel. And that they are set 90 degrees to each other so the holes line up.

As I set them in place I slide in a landscape spike to pin the corners together. The spikes should slide in without much effort. When I have the four panels pinned together I checked it again for level then tapped the spikes into the ground with the rubber mallet.

a man assembling cast concrete panels to make a raised bed in the garden — Tapping the steel rods into the ground with a rubber mallet

And that’s it. The thin concrete raised bed is done.

A 24″ x 36″ Thin Concrete Raised Garden Bed

Here’s a 24″ x 36″ box.

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I swapped out two of the 36″ panels for two 24’s. Then moved one wall in. And checked it for square and level before tapping in the spikes. And that’s a 2 foot by 3 foot box.

a man assembling cast concrete panels to make a raised bed in the garden — Setting the rear 24″ panel in place

a man assembling cast concrete panels to make a raised bed in the garden — Lining up a 24″ panel with a 36″

a man assembling cast concrete panels to make a raised bed in the garden — Bringing the overlapping corners together

a man assembling cast concrete panels to make a raised bed in the garden — Checking that the bed is square

a man assembling cast concrete panels to make a raised bed in the garden — Tapping the steel rods into the ground with a rubber mallet

a man assembling cast concrete panels to make a raised bed in the garden — A finished 24″ x 36″ concrete raised garden bed

Making a Taller Garden box by Stacking Panels

And this is the same size with a layer stacked on top. And I used some 3/8″ steel rod to secure the corners. And I cut that rod to 24″ lengths.

This steel rod I bought at a farm supply store. It’s used for electric fencing and came in 4 foot lengths. The diameter was exactly what I needed although I would prefer that it was galvanized. But, it’s fine for this demo bed.

a man assembling cast concrete panels to make a raised bed in the garden — Placing the first panel for the second row

a man assembling cast concrete panels to make a raised bed in the garden — Sliding a steel rod into the corner of the stacked garden bed

a man assembling cast concrete panels to make a raised bed in the garden — Sliding a steel rod to temporarily hold the front 24″ panel in place

a man assembling cast concrete panels to make a raised bed in the garden — Setting the back wall 24″ panel into place

That second steel rod was inserted just to temporarily hold that first panel in place as I worked my way around the box.

I find that stacking the second row is easiest if I already have a one row box completed and pined together. I’m starting with a layer that’s already level and square with holes lined up.

a man assembling cast concrete panels to make a raised bed in the garden — Sliding the last panel into place

a man assembling cast concrete panels to make a raised bed in the garden — Tapping the steel rods into the ground with a rubber mallet

a man assembling cast concrete panels to make a raised bed in the garden — Tapping the steel rods into the ground with a rubber mallet

thin concrete panels creating a raised garden bed — A 24″ x 36″ stacked garden bed

And if you don’t mind me saying, I think that looks pretty sharp.

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