Castor Ratings and Gel Weight: When a Full Bin Stops Being Movable

A 120-litre wheeled bin is rated for about 60 kg of working load on flat ground. Fill it with 30 litres of free liquid, add 7 kg of polymer, and you have put 37 kg of water into a bin that already weighed 20 — then the crew adds another 15 kg of solids because the lid still closes. The castors are the first thing to complain, and they complain by folding.

This is the quiet cost of gelling that nobody puts in the business case. Solidification converts a dripping bin into a heavy one, and heavy bins break equipment, floors and backs.

The weight arithmetic you need on paper

The polymer itself barely adds weight. What adds weight is the water it holds, which was already in the bin but was previously running out the bottom onto the yard. Gelling does not create mass; it stops you losing it. That is the point, and it is also the trap.

What breaks first

Castors, then the bin base, then the person pushing. A 75 kg bin on 75 mm castors needs a real push to start moving, and much more to steer on a slope or a threshold strip. Staff compensate by dragging, which loads one corner, and the base cracks at the insert within a few months.

The floor takes it too. A gelled bin dropped from the tailgate lands with its full mass on two castors. On a tiled or resin floor in a service yard, that is how you get star cracks.

Floor loading and the tailgate drop

Weight does not stop at the castor. A 100 kg bin resting on four 75 mm wheels puts roughly 25 kg through each contact patch, which is fine on concrete and marginal on a suspended slab, a resin coating or a tiled yard. Over a year of daily traffic you get hairline cracks radiating from the bin store doorway.

The tailgate is worse. Every lift ends with the bin coming down, and a full bin dropped from 300 mm lands with a force well above its static weight. Ask the collection crew to set bins down rather than drop them; most will, if someone has told them why.

The case that ended in a written-off bin

A contract caterer’s site had a ramp of about 1:12 between the kitchen door and the bin store. Bins had always been heavy. After gelling started, the crew began leaving bins at the top of the ramp and carrying bags down instead — which defeated the purpose and produced a new drip problem at the ramp head.

One Friday, a 240-litre bin at an estimated 105 kg lost a front castor halfway down. The bin went over, the lid popped, and roughly 25 kg of gelled waste spread across the ramp. Cleanup took two people ninety minutes and a pressure washer. The bin was written off; the base had torn at three of the four castor plates.

Keeping gelled bins inside their rating

• Check the rating plate on the bin — usually moulded into the base, not on a sticker.
• Cap the fill at 80 percent of the rated load and treat free liquid as part of the load, not as something that will drain away.
• Move to 200 mm castors on any route with a ramp, threshold or rough concrete.
• Set a two-person rule above 60 kg, and enforce it with a scale in the yard rather than a sign on the wall.
• Weigh a full bin monthly; a weight ticket is the only argument that survives a dispute about who broke what.

If your route has a ramp, dose to the low end of the range and accept a slightly wetter bin — or split the load into two smaller bins. A second 120-litre bin costs less than a back injury claim, and much less than replacing four bins a year. The polymer product range includes higher-absorption grades, but no grade removes water from the weight equation.