Round Concrete Garden Bed Casting from Molds

Here’s the blog post for the YouTube Video on making round end concrete casting for a raised garden bed using one of our patented ABS plastic molds.

I have a PDF summary of the concrete casting process and tools required for download. Get the Good Casting Practices guide.

Casting the Concrete Raised Garden Bed Panels

The 24″ mold produces a concrete casting that weights approximately 33 lbs and the 36″ panel produces one that weights approximately 50 lbs.

Background of the Garden Bed Mold Development

man with concrete castings on a bench — Kent introducing the new line of concrete garden bed molds

Hi everybody, I’m back with a brand new design for my concrete garden bed panels. And they’ve got curves!

I have three new concrete molds that have curved ends and a rounded inset. I have a 24 inch and a 36 inch length with curves on each end. Plus, I have a 36 inch long transition mold that casts a panel with one round end and a square end like my original design.

concrete castings and molds on a bench — Some of the castings from the new round end molds

overhead view on concrete castings and molds on a workbench — Three new round end mold designs

The transition mold allows you to link the new curved end panels to the square end original ones to make longer beds.

close image of two concrete castings and some tools on a table — The transition mold has a round end and round inset on one end. And a square on the other like our original panels.

I have a PDF summary of the concrete casting process and tools required for download. Get the Good Casting Practices guide.

Here’s some of the new raised garden bed configurations that can be assembled with this new design.

Round End Mold Bed Configurations

The simplest is four 24 inch panels in a square.

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animation still of a round end concrete raised garden bed — Four of the round end 24″ panels assembled in a 2′ x 2′ box

Here’s two 24s and two 36es.

animation still of a round end concrete raised garden bed — Two of the round end 24″ panels plus two 36″ assembled in a 2′ x 3′ box

Or four 36 inch panels in a bigger square.

animation still of a round end concrete raised garden bed — Four of the round end 36″ panels assembled in a 3′ x 3′ box

To make a longer bed you can use two 36 inch round ends with four of the transition panels.

animation still of a round end concrete raised garden bed — A roughly 3’x6′ box from two 36″ and four 36″ transition panels

Then with the addition of my original panels this bed can be made even longer. Here I’ve added two of the 36 inch originals.

animation still of a round end concrete raised garden bed — The original panels will fit the new round end transition panel

And they can be stacked to make deeper beds. (as I’ve covered in two previous videos)

animation still of a round end concrete raised garden bed — An example of the panels stacked to make deeper beds

Casting these new panels is done almost identically to my original design. Since I introduced these ABS plastic molds I have made some changes and improvements to the process to give even better results and I’ll focus more on those here.

I still will go through all the steps in case you are new to my channel and haven’t seen these concrete raised beds before.

Panel Weights

Using regular portland based concrete mix, the 36 inch panels weigh around 50 pounds. The 24 inch ones around 33 pounds.

round garden bed molds 12 — The 24″ panels weigh around 33 pounds

round garden bed molds 11 — The 24″ panels weigh around 33 pounds

Strong Workbench

You will need a stable, strong work table, or bench, that can support the weight for the number of panels you want to pour at a time.

round garden bed molds 13 — Matching benches

My bench is made with 4 by 4 legs, 2 by 6 aprons and stringers, and a 1 inch thick plywood top. It’s also on wheels so I can move it around my shop.

round garden bed molds 14 — A 1″ thick plywood top with hardboard

round garden bed molds 15 — A 1″ thick plywood top with hardboard

Level Workbench

It’s crucial that your workbench be level side-to-side and lengthwise. If not, then you won’t have uniform concrete thickness in your mold. A spirit level and some wooden shims will be needed to ensure your workspace is level.

round garden bed molds 16 — Checking level along the length of my bench

round garden bed molds 17 — Checking level along the length of my bench

Ambient Temperature

Ambient room temperature is important in predicting how fast, or slow, your concrete will solidify and cure. For predicable results I like to pour between 70 and 80 degrees. So, a stretch of consistent warm weather or a heated (or cooled) shop or garage is required.

round garden bed molds 19 — I have a mini split in my shop for temperature control

round garden bed molds 20 — I have a mini split in my shop for temperature control

Separate Work Area

The newly poured concrete will need to sit undisturbed for a few days so, your work area has to be away from other activities. You don’t want to move your molds unless you really need to. Moving them risks cracking the new concrete.

Tools & Supplies Ready

Be sure to have all your tools and supplies at the ready before you start any casting. Here’s a detailed list of everything I use for pouring. I also have a written detailed description of this process you can download and print from my website. Download here.

Alright, on to making the new panels.

Safety Gear

My safety gear includes glasses, gloves, and a P100 respirator or dust mask. Concrete dust and wet concrete is corrosive so always wear your gear.

round garden bed molds 21 — My safety gear

round garden bed molds 22 — Use caution working with concrete dust and wet concrete

Concrete Mixing

For mixing, I use a wheelbarrow, shovel, small trowel, high strength concrete mix, cold clean water, and a pail. This wheelbarrow has seen some heavy use.

round garden bed molds 23 — I mix my concrete in small batches on an old wheelbarrow

Concrete Vibration

To settle the mix I use a rubber mallet and sometimes a reciprocating saw without a blade.

round garden bed molds 24 — Tools to settle and vibrate the wet concrete

Mold Prep Tools

The molds and pipes will need to be prepped before pouring concrete. Tools and supplies include wire cutters, pliers, a tape measure, small bolt cutters, galvanized wire, galvanized wire grid, and a short length of 1 inch diameter pipe or dowel. I like the cutters on the fencing pliers shown here.

round garden bed molds 25 — Mold preparation tools I use

round garden bed molds 26 — The short length of plastic pipe for making a wire coil

Optional Panel Strengthening

This is to make the coil of wire that wraps around the pipes plus the grid that strengthens the concrete panel along it’s length. You may choose not to add these but, it doesn’t cost much or take any significant time to add a little extra insurance. So, I like to do it.

round garden bed molds 27 — The wire and grid are optional additions when casting the panels

Release Agents

To help release the concrete casting, I apply a finishing wax to the plastic mold and petroleum jelly to the pipes. I use paper towel or a cloth to apply the wax and a small brush to apply the petroleum jelly. The wax seems to give a nice smooth finish to the casting and the petroleum jelly really makes pulling the pipes easier.

round garden bed molds 28 — Wax and petroleum jelly as release agents for concrete casting

round garden bed molds 29 — The wax makes for a smooth finish on the concrete castings

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