Device to Replace Concrete Weights in Washing Machines
Washing machines are surprisingly heavy – and most of that weight is deliberate. Concrete blocks inside the machine serve a critical engineering function. A proposal to replace them with water-filled plastic containers sparked considerable debate. Here is a detailed look at why the weights are needed, what the proposal involves, and whether it could ever work in practice.
Concrete weights inside washing machines stabilise the drum during high-speed spin cycles, preventing the machine from walking, bouncing, or vibrating excessively. A concept to replace them with water-filled plastic containers would reduce shipping weight and carbon emissions – but faces significant engineering obstacles including space constraints, density differences, installation complexity, and the serious risk of internal water leakage.
Why Do Washing Machines Have Concrete Weights?
Opening the top or front panel of a washing machine reveals something that surprises most people – large concrete blocks, typically weighing around 25kg in total, bolted directly to the outer drum. To understand why they are there, it helps to understand what happens during a spin cycle.
When a washing machine spins at 1,200 or 1,400 rpm, the drum and its contents become a rapidly rotating mass. Even a small imbalance – a single wet towel on one side – generates significant centrifugal force. Without stabilisation, the outer drum would move violently, banging against the machine’s casing and potentially walking across the floor.
The concrete weights add mass to the drum assembly, reducing the ratio of imbalance to total weight. A 3kg imbalance in a 25kg drum assembly is proportionally much smaller than the same imbalance in a 5kg assembly – meaning less movement and vibration.
The combined weight of the drum assembly – drum, concrete blocks, bearings, and motor – makes the whole system harder to move. This prevents the machine from “walking” across the floor during spin.
Modern washing machines typically carry one weight on top of the drum and one either underneath or around the front. This distribution balances the assembly in multiple axes, not just left-to-right.
Older machines had metal outer drums, aluminium backplates, and cast iron bearing assemblies – all heavy in their own right. Modern plastic outer drums are much lighter, requiring more concrete to compensate. The shift to plastic is largely why current machines carry so much ballast.
The Environmental Cost of Concrete Weights
Twenty-five kilograms of concrete per machine adds up to an enormous cumulative weight across an industry that ships millions of units globally every year. The environmental argument for reducing this weight is genuinely compelling:
Heavier loads require more fuel to ship. Reducing each machine by up to 25kg – roughly a third of total machine weight – across millions of units represents a significant reduction in transport energy.
Industry estimates have suggested that replacing concrete weights with lighter alternatives could reduce CO₂ emissions by tens of thousands of tonnes annually across global appliance logistics.
Concrete production itself has a carbon footprint. Eliminating concrete weights entirely would reduce the embodied carbon of each machine – a benefit that compounds over the millions of units manufactured annually.
Lighter machines are easier and safer to handle throughout the supply chain – reducing injury risk for warehouse and delivery workers, and potentially enabling more efficient packing in shipping containers.
The Water-Filled Replacement Concept
The proposed solution is elegantly simple in principle: replace the concrete blocks with empty plastic containers during manufacturing and shipping. Once delivered to the customer’s home, the containers are filled with water to restore the ballast weight the machine needs to function correctly.
Water is freely available at the point of installation. Empty containers are lightweight and take up the same space as filled ones. The concept eliminates the need to transport 25kg of concrete per machine. It is a creative, low-tech solution to a genuine environmental problem.
Water is significantly less dense than concrete. Concrete has a density of approximately 2,300 kg/m³ – water has a density of just 1,000 kg/m³. A water-filled container providing the same mass as a concrete block would need to be more than twice the volume. Inside a machine with no spare space, this is a serious problem.
A typical 25kg concrete weight would need to be replaced with 25 litres of water – roughly equivalent to two and a half full washing-up bowls. Modern washing machines have no spare internal space of this scale. The outer drum already sits very close to the machine’s casing to accommodate larger drum capacities.
The Engineering Obstacles – In Detail
1. There is no room inside modern washing machines
The trend towards larger drum capacities has pushed the outer drum progressively closer to the machine’s cabinet walls. There is very little clearance between the drum and the casing – and this gap must be maintained to allow the drum to move on its suspension during wash and spin without striking internal components or the casing itself.
Fitting water containers large enough to provide equivalent ballast would require either a substantially larger machine cabinet – adding cost and negating some transport benefits – or a fundamental redesign of the internal layout. Washer-dryers are even more constrained, with additional drying components occupying space that washing machines do not need.
2. Filling the weights at point of delivery is impractical
Access to the drum weights in a fitted washing machine is extremely limited. The bottom weight, in particular, sits beneath the drum in the tightest part of the machine – completely inaccessible without partial disassembly. For the concept to work, weights would need to be repositioned to the top and front of the drum where a lid could be removed to add water. This itself requires redesigning where and how the weights attach.
There are also practical risks: water spilled during filling could contact electrical components inside the machine. If a container is not filled completely, the remaining air pocket allows water to move during the spin cycle – creating a shifting, unpredictable imbalance rather than a stable counterweight.
3. Water leakage could cause catastrophic damage
This is the most serious engineering concern. Drum weights are subjected to enormous centrifugal forces during high-speed spin. Even the current concrete weights are known to crack and come loose over time – a well-documented failure mode that can damage machines and cause significant vibration problems.
A plastic water container subjected to the same forces – and carrying 10-12 litres of water – would need to remain completely sealed and mechanically attached under all conditions for the entire life of the machine. If it cracked, split, or came loose, the resulting water release inside the machine could cause electrical shorts, corrosion, flooding, and potentially fire. The risk profile is significantly worse than a concrete weight simply cracking.
4. Sloshing water creates dynamic imbalance
A concrete weight is a static, fixed mass. A water-filled container introduces a dynamic element – the water can move within the container as the drum accelerates and decelerates. Road tankers address this problem with internal baffles specifically designed to prevent liquid surge. Without equivalent internal structure, a water-filled drum weight could actively worsen machine vibration rather than reducing it – the opposite of what is needed.
5. Freezing risk in cold environments
Many UK washing machines are installed in garages, outbuildings, or unheated utility spaces. In cold winters, water inside the ballast containers could freeze, expanding and potentially cracking the plastic. Any antifreeze additive would introduce a toxic chemical into a sealed system inside a domestic appliance – raising significant safety concerns.
6. Transit packaging conflicts
New appliances are shipped with polystyrene or cardboard transit packaging fitted inside the machine to protect the drum during transport. The additional space required for larger water containers would reduce or eliminate the room available for this packaging – potentially increasing transit damage rates and adding cost.
Could the Concept Be Made to Work?
Despite the obstacles, the engineering challenges are not necessarily insurmountable – they would simply require a fundamental redesign of how washing machines are built, rather than a retrofit of the current design.
If the outer drum were manufactured as a hollow double-skinned structure, the space between the skins could serve as the water reservoir – eliminating the need for separate containers entirely. This would be the most structurally sound approach, integrating the water reservoir into the drum’s mould rather than bolting separate components onto it.
One alternative suggested is using containers filled with a reactive compound – a material that absorbs water and then sets hard. This would deliver the installation convenience of water filling while eliminating the long-term risks of liquid under centrifugal stress. The result would effectively be a cast-in-place weight rather than a permanent liquid reservoir.
A simpler alternative to both water and concrete is using denser materials – cast iron or recycled metal – for the weights. These would be heavier per unit volume than concrete, potentially allowing smaller weights that take up less space. They could also be designed for recovery and recycling at end of appliance life, reducing the environmental impact of manufacture.
Perhaps the most effective long-term approach is to build machines that last significantly longer. A machine lasting 20 years has its manufacturing carbon – including concrete weights – amortised over twice as many wash cycles as one lasting 10 years. Durability is inherently the most eco-friendly design choice. Read our analysis: right to repair and appliance lifespan.
Why Does My Washing Machine Vibrate So Much?
Understanding drum weights also helps explain some common washing machine problems. Excessive vibration and noise during spin are among the most frequently reported faults – and the drum weight system plays a direct role.
| Symptom | Likely cause | What to do |
|---|---|---|
| Loud banging on spin | Unbalanced load, or drum weight loose or cracked | Redistribute laundry; inspect drum weights if banging persists |
| Machine walking across the floor | Uneven floor, worn shock absorbers, or severely unbalanced load | Level the machine; check shock absorbers |
| Vibration transmitted through floor | Suspended wooden floor, inadequate isolation | Use an anti-vibration mat; avoid spinning on suspended floors where possible |
| Drum weight cracked or broken | Normal wear, impact, or age – particularly common with concrete weights | Replace the drum weight – see our spare parts guide |
For more on noisy washing machines and vibration causes, see our dedicated guide: why is my washing machine so noisy? and our article on causes of a noisy washing machine.
Frequently Asked Questions
Why is my washing machine so heavy?
Most of the weight in a modern washing machine comes from concrete ballast blocks – typically around 25kg – bolted to the outer drum. These are needed to stabilise the drum during high-speed spin cycles. Without them, the drum would move violently, banging against the machine’s casing and potentially walking across the floor. The motor, drum, bearings, and casing add further weight, but the concrete blocks are the single largest contributor in most machines.
Could water-filled weights actually work in a washing machine?
In principle, yes – but in practice the engineering challenges are significant. Water is less than half the density of concrete, meaning a water-filled container providing the same mass would need to be more than twice the volume. Modern machines have no spare internal space for containers of that size. Additional risks include internal water leakage if a container cracks under centrifugal stress, dynamic imbalance from water sloshing inside the container, and freezing in cold environments. A double-skinned drum design that incorporates water as an integral part of the drum structure is the most technically plausible route.
Why do modern machines need more concrete than older ones?
Older washing machines had metal outer drums, heavy aluminium bearing backplates, and cast iron components – all of which contributed significant mass to the drum assembly without needing separate ballast blocks. The switch to lightweight plastic outer drums, driven by cost and manufacturing efficiency, removed this inherent mass – requiring it to be replaced with concrete ballast. Ironically, a return to heavier metal components would reduce the need for dedicated ballast entirely.
What happens if a drum weight breaks?
A cracked or broken drum weight – which is a known failure mode, particularly with concrete weights subjected to years of vibration – causes significantly increased noise and vibration during spin. In severe cases it can bang against the inner drum or casing, potentially causing further damage. If you hear loud banging that is not resolved by redistributing the load, a broken drum weight may be the cause. Drum weights can be replaced – see our spare parts guide or book a repair engineer.
Is there a better alternative to concrete for drum weights?
Several alternatives have been proposed or used. Cast iron or recycled metal weights are denser than concrete, meaning smaller weights could provide the same mass – potentially easing the space problem. Some manufacturers have experimented with composite materials. The double-skinned drum concept – using the drum structure itself as a water reservoir – remains the most elegant theoretical solution but would require a fundamental redesign of how washing machines are engineered. For now, concrete remains the industry standard because it is cheap, dense enough to be practical, and well-understood.
My washing machine vibrates badly on spin – is it the drum weight?
Excessive vibration on spin can have several causes – an unbalanced load, a worn or failed shock absorber, a machine that is not level, or a cracked or loose drum weight. Start by redistributing the laundry and checking the machine is level on stable, solid flooring. If the problem persists, it may be worth having the machine inspected. Read our full guide on noisy washing machines and washing machines that jump and bang on spin for more detailed diagnosis.
Whether it is a drum weight issue, shock absorber fault, or something else, our engineers can diagnose and fix the problem.
Hello Liz. Unfortunately all washing machines will have problems on a suspended wooden floor. Miele are without doubt the least likely washing machines to shake about but even they are not designed or recommended to be used on a suspended wooden floor. It’s even possible (ironically) that with the Miele being so heavy it could cause even more vibration. Washing machines need to be on a solid well supported floor.
Hi. This is all very interesting as I have a problem that relates to this. I am currently looking to replace a washing machine in an upstairs converted flat with suspended wooden floors and have been searching and enquiring about this to try and find the least vibrating machine on spin as the person below has complained that the whole place shakes and also the kitchen wall cupboards in my flat rattle away when the machine has been spinning. Do you think it’s worth paying the extra for a Miele or maybe Bosch machine to try and minimise the vibration noise? or in this situation will any machine be as bad ? I would appreciate your input if you can help advise. Thanks
Indeed Riccardo. If all washing machines were only made as well as Miele it would reduce far more carbon emissions than this weight replacement idea.
The CO2 from transport is, essentially, a one-off that happens once per new machine. The CO2 from producing the concrete block is also a one-off, unless the concrete block breaks.
I think a good solution to the problem is to use a weight that doesn’t break, can be recycled or even re-used, and a washing machine that lasts longer, thus meaning the environmental impact takes place one per 15 or 20 years instead of once every 4 years.
Perhaps the weights could be made of cast iron and the machine built to last a couple of decades, as some manufacturers are already doing. This water weight idea sounds like a ‘solution’ to a non-problem. Probably water weights will be even less reliable than concrete weights, which in turn were less reliable than the iron weights they have largely replaced.
Hello Geoff. The Hoover washing machines I specialised in (and used for one of the photos) had just one tub weight hung at the bottom of the metal tub. That weight combined with the metal outer drum (tub) and the aluminium backplate was enough to keep the machines steady. Some brands might have chosen to have smaller weights distributed around the tub. Many washing machines also had big cast iron spiders with bearings in attached to the back of the tub that were as heavy as a drum weight. Since they all moved onto plastic outer drums they all need a lot more weights.
If the shock absorbers could be good enough to dampen virtually all outer drum movement then they could have the outer drum and weights closer to other parts and the casing. However, that would also increase costs. The whole idea could end up adding quite a lot to the cost of a washing machine because of all the redesign and installation costs. The only way I can see it taking off is if the government really needs it to happen to offset carbon emissions. Then increases in costs to consumers becomes collateral damage so to speak.
I also mention the moving water problem in my article although I only give it one sentence. The freezing water issue is one I hadn’t thought of. Many washing machines are kept in garages or out buildings. It would need to get pretty cold to freeze water inside the blocks but it’s not impossible and it would potentially be a problem if it cracked the blocks.
Yes Bob, that’s an interesting possible solution to the leak concern.
The concrete weight is used for damping, but I can also recall years ago with smaller metal drums that they still required two and occasionally three concrete block to absorb the energy. However there maybe a way of reducing some of these blocks weights by using a combination of a shock absorber, similar to those used on vehicles and on some industrial equipment, and a concrete weight.
There is also the fact with water that unless the container was completely full then the water sloshing around could exacerbate the problem. (Road tankers have dividers inside the tank to prevent liquids sloshing around, besides making the vehicle uncontrollable but also can tip it over.) There is also the fact that if in a cold area in certain parts of the country, and particularly more northern parts of the world, the water could freeze and rapture the container. Some form of antifreeze would be required that is likely to be toxic. The whole thing gets messy, from filling and installation perspectives as well as from possible leaks.
Maybe the answer is a quick setting concrete mixture contained within containment that water is added to and allowed to cure. This would get over the transit and locating the machine problem with weight, but does not get over the issue of lack of room within the machine’s casing.
The “tanks” that are to be filled with water could have a reactive compound inside that absorbs the water and then sets hard thereby avoiding the chance of leaks.I seem to remember such a system being described to me a few years ago but at the moment i can’t recall what the aplication was used for.