Why does the mulch always disappear under the swings?

Because three forces work on the same spot. Feet dig in on every launch and landing, the seat scuffs the surface at the bottom of the arc, and children drag material outward as they slow down. The loose fill does not vanish, it moves. You will usually find it piled at the ends of the swing arc and against the border.

Do rubber swing mats actually help?

They help with wear and they can hurt with depth. A mat stops the seat and feet from scouring the material directly, which slows the loss. But a mat laid on top of loose fill gets undermined, lifts at the corners and becomes a trip edge, and it can reduce effective depth beneath it. Recessed, anchored mats rated for the fall height work. Loose mats do not.

How often should you rake under a swing set?

Weekly during the busy season for a well used public bay, and at minimum monthly everywhere else. Raking is not cosmetic. It moves the berm at the ends of the arc back under the seat, which is the cheapest depth you will ever recover. Measure with a probe at the same time rather than judging the level by eye.

Can you put poured rubber only under the swings?

Yes, and it is a common hybrid. A poured-in-place or tile insert covering the scour zone inside a loose-fill playground removes the worst maintenance point. The catch is the joint: the insert must be flush with the surrounding loose fill, the loose fill must be kept topped up to stay flush, and the insert needs its own ASTM F1292 rating at the swing fall height.

Why is there a puddle under my swings?

Because the hollow is now the low point of the play area and water runs to it. A scoured bay collects runoff, the loose fill sits wet, and wet wood fiber breaks down into soil faster and loses impact performance. Fix the depth, then check that the base under the bay still drains and that the geotextile has not been torn through.

Surfacing under swings: scour, mats and depth loss

Why the swing bay is always the worst spot

Every other piece of equipment loses surfacing gradually. A swing bay loses it systematically, because the activity itself is a material-moving machine.

Three things happen at once. Children dig their feet in to launch and again to stop, which excavates the spot directly under the seat. The seat itself scuffs the surface at the bottom of the arc, especially with older children who ride low. And feet dragging forward and back push material outward along the line of travel. The result is a consistent, recognizable pattern: a hollow under each seat, and a berm of displaced material at each end of the arc and against the containment border.

That pattern matters because the hollow is exactly where the fall is most likely. A child who comes off a swing leaves it at the bottom or at the ends of the arc, over ground from which the surfacing has already been removed. The swing safety page covers the rest of the swing hazard picture, and swings covers seat types and bay layout.

How fast depth goes

Depth loss is driven by use, not by time, so calendar rules are weak. A single busy elementary school bay at recess can move visible quantities of material in a week, while a lightly used bay in a private yard holds depth for a season. Treat these as planning assumptions to be replaced by your own probe readings:

Setting	Realistic depth check interval	Realistic top-up interval
School or park, heavy daily use	Weekly in season	Monthly redistribution, quarterly new material
Childcare or church, moderate use	Every two weeks	Quarterly redistribution, annual new material
Backyard, family use	Monthly	Twice yearly redistribution, annual new material

Suggested starting intervals for swing bay depth checks and top-ups. Replace them with your own probe data after one season, because usage, drainage and material all shift the numbers.

The distinction between redistribution and new material is worth keeping. Most of what you have lost is still on site, in the berm. Raking it back is free and it restores real depth. New material is only needed once the total volume in the bay has genuinely dropped, through breakdown, wind, or migration past the border. Surfacing upkeep sets both tasks against a schedule.

Swing mats and wear pads

A swing mat is a rubber pad placed in the scour zone under a seat. The intent is sound: put something durable between the wear and the loose fill. Whether it helps depends almost entirely on how it is installed.

What goes wrong with a loose mat. Laid on top of loose fill, a mat is undermined within weeks. Material washes and kicks out from beneath it, the mat sags into the hollow, and the edges lift. A lifted edge inside a use zone is a trip hazard and an obstruction, and it is one of the most common findings on swing bays that have a mat. It also hides the problem: the hollow keeps deepening under a pad nobody removes to check.

What works. A mat that is set flush, anchored, and rated for the job. That means recessing it so the top sits level with the surrounding compressed surfacing, fixing it with the manufacturer's anchors or stakes driven below the surface, and checking that the mat plus whatever is beneath it carries an ASTM F1292 rating at the swing's fall height. Some mats are tested as a system with a specified base. A mat is not automatically a safety surface just because it is rubber.

Mat approach	What it does well	What to watch
Loose mat on top of loose fill	Nothing durable	Undermining, lifted edges, hidden hollow
Recessed, anchored wear pad	Stops direct scour, keeps the level	Needs re-leveling as surrounding fill settles
Unitary insert across the bay	Removes the maintenance point entirely	Joint detail, cost, its own F1292 rating

Three ways of protecting a swing bay, and the failure mode of each. The middle row is the common compromise and it needs the most ongoing attention.

Trip hazards and edging covers how a raised edge is assessed, which is the test any mat has to pass at every inspection, not just on the day it goes in.

Unitary inserts under swings

The durable answer is to stop using loose fill in the scour zone. A poured-in-place or tile insert, sized to cover the full swing use zone or at least the scour band under the seats, ends the raking cycle for that bay.

Three details decide whether it works.

The rating. The insert needs its own ASTM F1292 report at the swing fall height, which for a to-fro swing is measured from the pivot down to the surfacing. That is often the highest fall height on the whole structure. Poured-in-place rubber covers how that thickness is specified and tested.
The joint. Where the insert meets loose fill, the loose fill will settle and the insert will not. That leaves a step. The only maintainable detail is one where the surrounding fill is kept topped up above the insert edge, so any transition is buried rather than exposed.
The base. A unitary insert needs a prepared, drained base to sit on. Pouring rubber into a hollow scraped out of a loose-fill playground is a guaranteed failure. Drainage and base layers covers what goes underneath.

Inserts are also the usual answer under inclusive swings, where a platform or harness seat is used by a child transferring from a wheelchair and the approach route has to stay firm and stable under ASTM F1951³.

Drainage in a scoured hollow

Once a hollow forms, it becomes the low point of the play area, and water follows the low point. That turns a maintenance problem into a materials problem.

Wet loose fill compacts harder, breaks down faster, and in cold climates freezes into a solid mass that offers almost no impact attenuation. Wood fiber sitting in standing water composts into soil, and the bottom two or three inches quietly stop counting as surfacing even though a probe still reads full depth.

So when you fix a hollow, check three things below the surface: whether the geotextile has been torn or worn through, whether the aggregate base beneath is still open or has silted up, and whether water leaving the bay has anywhere to go. Fixing the depth without fixing the drainage buys you one season.

The fix order when a hollow has formed

Work in this sequence. Doing it out of order wastes material.

Measure before you touch it. Probe under each seat, at both arc ends and at the border. Write the readings down so you can tell next season whether anything changed.
Rake the berms back. Most of the missing depth is within six feet of the hollow. Pull it back under the seats before ordering anything.
Inspect what you have exposed. Geotextile condition, base condition, standing water, exposed footings, exposed hardware, anything sharp.
Repair the base and drainage. Patch or replace torn fabric, restore the aggregate, and make sure the bay is not the sump for the whole site.
Top up to installed depth, not compressed depth. Order using the coverage figures in how much mulch do I need and allow for settling.
Water and let it knit. Fresh wood fiber is loose and does not perform or propel like settled material until it consolidates.
Set the cadence and the marker. A weekly or monthly rake, a depth probe at the same points, and a visible mark showing the target. Add it to daily and weekly checks.

What to do next

If you are maintaining an existing bay, the highest value change is not a product, it is a rake and a probe on a schedule. Most swing bays that fail a depth check are not short of material, they are short of redistribution.

If you are rebuilding or designing, decide the swing surfacing separately from the rest of the site. Swings carry the highest fall height and the highest wear on most playgrounds, which is a reasonable argument for spending unitary money on that bay and loose-fill money everywhere else. Confirm the fall height and the use zone dimensions with fall height and use zones, then price both options against each other in the surfacing cost comparison.

Surfacing under swings