Make Lightweight Concrete Garden Boxes – Vermiculite Aircrete PART 3

Make your own Lightweight Concrete Garden Boxes! This is PART 3, showing options to make your garden boxes from lightweight concrete.  You can build these forms and precast your own 48″, 36″, or 24″ reinforced lightweight concrete panels that link together to make long lasting and durable concrete garden boxes. See the complete build video that shows step-by-step how to make the wooden molds for the precast garden boxes.

Here is the weight of 3 cured panels made from regular concrete: . 48″ – 69lbs, 36″ – 50lbs, 24″ – 33lbs.

See the Youtube Video and download the Plans.

This is part three of my series on casting your own reinforced concrete garden box panels. These panels link together to make long lasting rot proof garden boxes.

make Lightweight Concrete Garden Boxes PART 3 - Aircrete Vermiculite Lava Rock
Watch this video on YouTube.

Background for the Cast Concrete Garden Box Project – PART 3

Link-together concrete garden boxes
These garden panels link together with rebar

In Part 1 I made the forms from plywood. In Part 2 I simplified the design to make the forms easier to build. And for this video, I’ll cast the panels with lightweight concrete.

Lightweight concrete garden panels
One of the aircrete test panels

I had many viewer requests to make the panels lighter so I did some research into this. It turns out there are MANY ways to make lightweight concrete so, to simplify things, I decided to focus on just three formulations.

I wanted to use readily available materials that you could pick up at any big box, building, or garden supply store. Or that you could easily order online.

Main Formulations

Three lightweight options covered: Lava Rock, Vermiculite, and Aircrete
Three lightweight options covered: Lava Rock, Vermiculite, and Aircrete

For the first mix I substituted the gravel aggregate for lava rock, in the second mix I used fine vermiculite. And in the third I’ll replace the sand AND gravel aggregate for foam and try an aircrete version of the garden panel.

I’ll show the mixing, pouring, and unmolding, then look at the weight and durability results.

If you haven’t seen Part 1 and Part 2 of this series then you might get more from this video if you watch them first.

I’ll be using the forms I built in Part 1 and Part 2.

I let all the test panels fully cure for a month, keeping them damp and covered. Then I let them dry for a week or so before weighing.

So here’s the first formulation.

Lava Rock Lightweight Concrete

So this will be my first attempt at making some lightweight concrete. This blend uses portland cement, lava rock, sand and some glass fiber for reinforcement.

Ingredients for the Lava Rock Concrete Tests
Ingredients for the Lava Concrete Tests

You add about one pound of this fiber per cubic yard of concrete.

Glass Fiber for concrete reinforcement
Glass Fiber for concrete reinforcement

So when I calculated how much I needed per batch it came down to a third of an ounce per 48″ panel. So I just used a pinch. So here’s the proportions I used for the first attempt at Lava concrete:

one part Portland Cement

three parts Lava Rock

two parts Sand

a pinch of Glass Fiber

Lava Rock – 1st test

Lava Rock Concrete - 1st Test

These proportions are by volume.

I put the sand, lava rock, and fiber in the wheelbarrow first, and blended that before I added the Portland cement. Once that was well mixed, I slowly added water. I realized as I was doing this that it wasn’t looking as smooth as I wanted and it looked quite lumpy. I thought well, I’ll go ahead with it and put it in the form.

Shovelling Lavarock concrete into a form

I used a reciprocating saw, without the blade, to vibrate the form and settle the concrete mix. Then I laid in a piece of reinforcing wire mesh.

Lava Rock Concrete with embedded galvanized hog fence of reinforcement
Lava Rock Concrete with embedded galvanized hog fence of reinforcement

This galvanized wire mesh is cut from a large hog panel fence I bought from my local farm supply store. Then I topped up the rest of this and vibrated it some more. I tried to smooth it out with a trowel and it wasn’t coming out very well. But in the bottom of the wheelbarrow I had lots of sand mixture left over, so I just did the best I could with that.

For my second attempt I changed the ratio a bit. I went with one part portland cement, two parts lava rock, and three parts sand and again a pinch of glass fiber.

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