Building a retaining wall in the conventional ways (above) is not a trivial matter. So DIYers have come up with an interesting trick: Rather than messing around with mortar, they lay the walls down like Lego pieces, using concrete while it’s still in the bag.
That’s right, the idea is that you don’t open the packaging. Once the bags are laid, you wet everything down thoroughly with a hose, saturating all of the bags.
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Once the concrete sets up, you can either wait for the paper to biodegrade, peel it off, or burn it off.
Prior to wetting the concrete, you can easily drive rebar into the bags as reinforcement.
You can also use the technique to build sunken fire pits.
Once cured, you can tell that these were made using bags, but I don’t find the effect unpleasing.
If you want to use “bricks” that are smaller in size than your standard concrete bags, you can put in some extra work and re-bag the concrete in smaller lunch bags. That’s what the fellow below did to create a retaining wall, and even a short series of steps, to brick in this culvert:
I wonder if, as in the entry about fenceposts, you can simply wait for a thunderstorm and forgo the hose step.
Source: core77