building retaining wall with unopened bags of ‘concrete’ – often in the pics we see actually cement bags, looks like. Seems to be a new fashion or something. I see pics of very large areas done like this: very large retaining walls. The expense must be enormous. But they seem to have done it.
Seems crazy to me. So I asked my old friend chatgpt, ‘unreliable’ as he is, what he thought and he said:
Building retaining walls using unopened bags of cement (often mistakenly called “concrete”) is an unusual and highly questionable practice. Here’s a breakdown of the potential worth and risks of this procedure.
What Might Be the Intended Idea?
Cost-saving shortcut: People may think that stacking bags is cheaper or faster than using proper concrete blocks or poured concrete.
Hardening effect: The theory is that over time, rain will soak the bags, causing the cement inside to set and create a solid structure.
Aesthetic improvisation: Some might find it a quick DIY method without needing formwork or professional skills.Serious Problems and Risks
Structural Integrity
Uncontrolled hydration: Cement requires precise mixing ratios with water. Rainfall or moisture may not distribute evenly through the bag, leaving portions soft and useless.
Weak, brittle results: Even if part of the bag hardens, it’s unlikely to achieve the strength of properly mixed concrete.
Erosion over time: Bags won’t bind together reliably, and any hardened parts will still crumble due to poor compaction and inadequate bonding.
Durability and Weathering
The paper or plastic bag material will degrade, leaving exposed cement prone to cracking and erosion.
Rainwater can wash away uncured cement, weakening any structure or introducing voids within the wall.
Load-Bearing Concerns
Retaining walls need to withstand lateral pressure from soil, especially after rain. A “cement-bag wall” won’t handle heavy loads and is prone to collapse, leading to property damage or injuries.
Aesthetic and Environmental Impact
It looks unprofessional and quickly deteriorates into an eyesore.
Cement can also leach alkalines into the soil, which may negatively affect plants or groundwater in the area.
Misuse of Materials
Cement is not concrete—it’s just a component. Without aggregates (like gravel or sand), the mixture won’t achieve proper strength, even if it sets.Situations Where It Could Have Some Limited Use
While this method is generally unsound, there are rare situations where people might find temporary use:
Emergency flood control barriers: As a very temporary solution, stacked cement bags might prevent some water flow.
Landscaping experiments: If the goal is just to create a garden feature that won’t bear significant loads, it might serve briefly—although other options (like rocks or actual concrete blocks) would still be better.What about if it were really ‘concrete’ ? concrete can be bought in bags, just needing water, they advertise. Incredibly expensive way to buy concrete. But:
Bagged ready-mix concrete—which includes cement, sand, and gravel—has become common and only needs water to activate. However, using unopened bags of concrete for retaining walls is still problematic, though it shifts the discussion slightly. Below are the specific considerations if someone were to use unopened bags of concrete for such a project.
What Happens if Unopened Bags of Concrete Are Used?
Hydration Still Uncontrolled
Rainwater won't permeate the bag evenly. Some areas of the concrete mix will harden, while others might remain dry or poorly cured.
Even if part of the bag sets, it’s likely to form brittle and weak sections that don’t bond together properly. Proper concrete needs controlled water content and proper compaction to achieve strength.
Bag Decomposition Issues
Whether paper or plastic, the bag’s material will eventually degrade, exposing the semi-hardened chunks inside to weathering and erosion. Once exposed, these sections will crack or crumble, weakening the wall.
Lack of Compaction and Bonding
In poured concrete, compaction (removal of air pockets) and continuous bonding between layers are crucial for strength. Stacked bags won’t achieve this; instead, you'll get a pile of poorly bonded lumps.
Failure to Withstand Lateral Pressure
Retaining walls are subject to lateral earth pressure, especially when soil becomes saturated with water. A bag-wall won't be able to handle these loads, leading to shifting, bulging, or collapse over time.Would There Be Any Value in Using Unopened Bags of Concrete?
Temporary Use
In temporary projects, such as flood control barriers or very small garden beds, using unopened bags might offer a short-term solution. For example:
If stacked securely and left undisturbed, the bags could act as a low barrier for a season or two.
However, this is not a proper long-term solution since degradation will start relatively quickly.Can This Method Be Improved?
If someone is set on using bagged concrete for convenience, here are a few better alternatives:
Open the Bags and Add Water Properly
Dump the concrete into a wheelbarrow or mixer, mix thoroughly with water, and pour it into molds or stackable forms.
Use Bags as Formwork (Temporary Molds)
You could use the unopened bags as temporary molds. After stacking them, pierce holes to add water manually, and let the bags cure for a short period.
Later, peel off the bags (before they degrade) to leave hardened blocks behind. Even so, the blocks will be imperfect without proper mixing or compaction.
Dry-Stack Blocks and Mortar Fill the Gaps
If ease of use is the goal, concrete blocks with mortar or dry-stack blocks would be much more reliable and durable than using unopened bags.Conclusion
Even with ready-mix concrete, using unopened bags to build a retaining wall is not advisable. While this approach might result in some sections hardening, the lack of controlled hydration, compaction, and bonding makes it structurally unreliable for anything beyond short-term, low-load situations.
If you want to build a lasting and safe retaining wall, properly mixing and pouring concrete or using interlocking blocks is the way to go. This ensures your wall will handle soil pressure and weather exposure without crumbling away.
Verdict
Building a retaining wall from unopened cement bags is not advisable. It’s an unsound practice, both structurally and aesthetically. If you’re looking for a cost-effective retaining wall, alternatives such as:
Dry-stacked stones or interlocking blocks
Gabion walls
Railroad ties (for small projects)will be far more reliable, visually appealing, and safer in the long run.