Make your own Lightweight Concrete Garden Boxes! This is PART 3.6, showing options to make your garden boxes from Air Crete. 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.
Here is the weight of 3 cured panels made from regular concrete: . 48″ – 69lbs, 36″ – 50lbs, 24″ – 33lbs.
Background for the Cast Concrete Garden Box Project – PART 3.6
This is another follow up post to Part 3 of my series on making garden box panels from lightweight concrete. And in this episode I’ll be pouring more aircrete.
I’ve been making these link-together concrete panels for rot proof garden boxes for a few years now.
In Part 3, I worked on concrete blends to find a mix that was light, strong, and durable. And the aircrete that I made in that episode had some issues and it failed the durability test. And it also cracked and distorted as it cured and dried.
So in this video I’ll make another attempt at casting a strong and durable garden panel from air crete. And also try some colour additives to see have that looks.
I’ll show the foaming agent, mixing the cement, pouring, and finally unmolding. Then look at the weight and durability results as compared to regular gravel-based concrete.
If you haven’t seen part 1 and 2 of this series then you might get more from this video if you watch them first. As I won’t be covering all the steps needed to make the forms and prep them for casting.
I’ll be using the plywood forms I built in part 1 of the series. I have plans available here.
The aircrete is made from only a few ingredients: Portland cement, shampoo to create a foam, and some glass fiber for extra strength.
So I begin by diluting the shampoo in water. 15 fluid ounces of shampoo to 2.5 gallons of water.
This will be the dilution that I’ll use to create the foam. I use Suave Daily Clarifying Shampoo as my foaming agent.
I like it as it makes a very good dense foam, it’s cheap, and it’s widely available.
I stir this with a paint mixer attachment for my drill on a low setting — just to dissolve the shampoo in the water.
In Part 3 of this series I was able to make foam with window screen attached to an egg-beater style mixing attachment on my drill.
I simply poured some of the shampoo dilution in a pail and whipped it up into a foam with the mixer.
It worked so well right out of the box that I’d recommend it to anyone who wants to get into making aircrete.
I simply poured the shampoo dilution into the tank, connected my air compressor hose and started making a dense shaving-cream-like foam instantly.
I use a digital scale to weigh my gradients. This time around I use 15 pounds of portland cement, about 8 and a half pounds of water, 3/4 of a pound of foam and a pinch of fiber.
I slowly add the portland cement to the water while spinning the slurry with a paint mixing attachment on a drill. I want a smooth, well blended slurry here with no clumps or dry cement on the bottom or sides of the pail.
I’ll add the glass fibre and mix that in.
Then I stop and use an improvised stir stick from a wooden dowel to hand stir the cement mix. This helps free up any clumps.
With the slurry now ready, I connect the air hose to the foam mate and start making foam. Once its flowing thickly I add some to the slurry pail.
I have a mark on my stir stick that approximates the amount of aircrete I need to fill one 36″ form. In this case, using a five gallon pail, I need the pail filled to the 8 inch mark as a minimum.
I’ll use my mixer to blend it all evenly. And hand-stir to make sure that everything was blending right to the bottom of the pail.
Then I poured the aircrete into the form — giving it a bit of a jiggle to help settle it into the corners.
Once the aircrete begins to thicken, I gently lay in a galvanized wire reinforcing grid. Pressing it down so it settles right in the center. And smooth the surface with a trowel.
In the second blend I’ll use the same amount of cement and water, a bit less foam and almost a pound of perlite.
I want to see how this light volcanic sourced rock blends with aircrete and if it adds any strength or durability. Perlite is a hard, highly porous material made by super-heating volcanic glass.
As before, I slowly add the cement to the water. Then add the glass fibre. Hand stirring to free up any clumps from the sides or bottom of the pail. Then add the foam and blend it again with the drill.
This worked very well. The aircrete had a lumpy consistency but poured well into the forms. I jiggled the form to settle it, then added a bit more to top it up. I smoothed it with a trowel and left to thicken.
After a few minutes I laid in a double wire grid. I wanted to see if adding two layers of wire grid worked better than just one. To make this grid I simply folded a section of the galvanized fence in half and wrapped the ends into a flattened tube.
I pressed this in and smoothed with a trowel.
For the next test I’ll add about 1 fluid ounce of red liquid cement colour to the water. I’ll leave out the fibre on this one. I make a smooth cement slurry and add the foam. This air crete came out a light chocolate brown colour. I blend it well and pour it into a form. And I’ll lay in a double wire mesh and smooth with a trowel.
The final test I’ll add black cement colour to the water. Leave out the fibre, but add perlite. I kept the density of the aircrete fairly consistent through these tests. Varying the fibre, perlite, and grid. And a bit of colour additives for fun.
I blend as before and pour into the form. When it starts to solidify I’ll add a single wire grid for reinforcement.
When the aircrete solidified that afternoon I covered the forms with plastic and left them for a couple of days.
I remove all the screws from the form, gently wiggle the sides to free them, then remove the panel from the base and stand it on one side — and then remove the ends. Aircrete is fun to make. It’s involved for sure but not very labour intensive. Everything is blended in a pail with a drill. It’s light by default and has many uses.
All the panels came out of the forms without issue. They all felt sound and solid. There were no cracks or any signs of warpage. I lined them up on sawhorses to get a shot of them before curing.
These panels where submerged in water in an improvised tank that was a recycled bathtub. They soaked for two weeks then pulled out and allowed to slowly dry in my shop for another two weeks.
Then I weighed the panels and lined the first two I cast on the lawn and ran a line trimmer against them as a test of durability. I wanted to see how this denser aircrete held up to impact of the spinning line. And I wanted to see if the perlite helped.
These new panels did very well in the durability test. There was little damage to the surface. The perlite didn’t make much difference in this case, and didn’t increase the durability. Without a hard aggregate in the mix, this form of concrete is always going to be weaker. The trick is to find the right weight to strength balance for your application.
The panels were very close in weight and averaged 56% lighter than regular concrete. This denser aircrete has a very good finish and it faired much better than the previous ones in the durability line trimmer test. There’s some damage, but it looks minimal. And looks to be the same in the panel with perlite added.
I don’t see any cracks or warping of any of these panels so I think the bigger ratio of portland to foam was the answer. It appears if you want strength and durability improvements you really need more cement. If that changes over time I’ll update my blog post.
At this point I don’t see a huge advantage to adding perlite to aircrete. Or to doubling up the wire grid. But, it doesn’t seem to hurt either. So maybe the takeaway here is that it’s easy to add both if you wanted.
The liquid cement dyes worked well and it was easy to add. The next time I’ll even more to get deeper colours.
Darwin’s Foam Mate worked very well. It allowed me to quickly make foam just when I needed it. And just as much as I needed. So I can certainly recommend that.
In the next episode I’m going to make aircrete with CSA cement instead of Portland. And that will be up in about a week or so.
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