Concrete Raised Garden Bed Molds- Plastic ABS

Leave to Cure for Two Days

I like to leave the concrete in the forms for 2 days at least. Longer if your temperatures are cooler.

Adding Additional Strength

If you want to add more strength then you can embed some wire in the concrete in the form of a stiff wire grid down the middle. I use some concrete mesh sections that I cut with small bolt cutters. This mesh is 6″ x 6″ – 9 gauge (0.15″ diameter, 4mm)

a section of wire grid is sized to the mold cavity space

I also add a spiralling wrap of galvanized fence wire around the pipes. This wire is 12 gauge (0.10″ diameter, 2.5mm)

You can wrap this wire around a section of larger diameter pipe, then I bend the ends for safety. I run the pipe through the center of this spiral when I’m prepping my molds.

wrapping galvanized fence wire around a larger pipe to create a spiral

bending the ends of the sharp cut fence wire — wrapping galvanized fence wire around a larger pipe to create a spiral

These additional steps are optional. But, they are easy to do and not very costly. I have a blog post link here for all the details of any additional items or tools you might need.

close up of the galvanized fench wire wrapped in a spiral around the hole forming pipes — close up of the galvanized fence wire wrapped in a spiral around the hole forming pipes

For a few dollars more per bag you can buy high strength concrete mix.

high strength concrete is a good idea

High Strength Concrete

And with or without this additional wire and grid I think it’s a good idea to upgrade your concrete mix to a high strength blend. You end up with a stronger panel and a tough, smooth finish.

I rotate the wrap wire upwards while I fill the form half way. Then shake and vibrate it.

rotating the wrap wire up and out of the way in preparation for filling the concrete form

adding concrete to the mold with a shovel — rotating the wrap wire up and out of the way in preparation for filling the concrete form

And this small trowel helps me get some concrete in behind the pipe where the wire wrap is.

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using a small trowel to move wet concrete behind the wire wrapped pipes

Then lay in the grid before topping up the form with more concrete.

setting the wire grid onto the wet concrete

Instead of the wire mesh you could use a section of galvanized hog panel or some pieces of rebar layed down the middle.

adding more concrete over the wire grid to top up the mold

troweling the surface of the wet concrete smooth

Unmold the Concrete Panels

So, the first concrete pour sat for two days.

uncovering the molds after two days

Now we need to flip the molds upside down on your workspace.

lifting the loaded mold underneath while gripping the lapped corners

It’s best to lift the mold from underneath and place the concrete against the edge of the bench. Then slowly and gently rotate it over.

rotating the loaded mold over on the bench while maintaining contact with the edge

You don’t want to stand the form on its thin edge or flange with 50 pounds of concrete in it.

Now gently lift the ends in an alternating fashion to free the casting from the mold.

gently flexing the plastic mold from end to end to free the casting

Any excess oil on the concrete can be wiped away with a clean rag. I’ll set this first one aside for now.

a good concrete casting will come out of the mold cleanly

When pulling upwards on an end, apply a little downward pressure with your other hand toward the middle of the form. The casting should come out clean.

wiping any excess oil from the fresh concrete casting

The mold can then be wiped down with a clean cloth to remove any concrete dust or pieces and any leftover mineral oil.

the mold can be quickly cleaned with a dry clean cloth

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