Silt bags catch sediment before it leaves a construction site, either by filtering pumped water or by holding loose fill at site boundaries.
The name covers two different products. Filter bags sit on the end of a dewatering pump and strain silt out of the water. Sand-filled bags stack along perimeters, drain outlets and bunds to trap sediment-laden runoff before it reaches a waterway.
This guide covers both meanings of silt bags, the different materials, when each works best, and how silt bags fit alongside silt fences and other sediment control products on an Australian job site.
Building an erosion and sediment control plan? Browse the erosion control products or contact the team for trade pricing on bulk sediment control orders.
Silt bags sit in the middle of every erosion and sediment control plan. They trap soil particles in moving water before that water reaches a drain, creek or gutter.
Getting sediment off a site cleanly is not optional. It is required under most council and state environmental rules across Australia.
The two common forms work in different ways. A filter silt bag attaches to a dewatering pump hose and traps fines as the water passes through the geotextile wall.
A sand-filled silt bag holds loose sand or gravel inside a woven fabric bag, and gets stacked on the ground to redirect and slow runoff. Both buy time for soil to settle out rather than ending up downstream.
A filter silt bag is a large woven geotextile bag with a reinforced inlet at one end. The discharge hose from a dewatering pump feeds straight into the bag, and the fabric wall filters out silt and fine sediment as water seeps through.
Clean water drains away. The trapped sediment stays in the bag and goes to spoil when the bag is lifted and tipped.
These bags suit excavations, stormwater pit work, piling jobs and any time water has to come out of a hole and cannot run straight onto the road or into a drain. They are low-cost, fast to deploy and need no power beyond the pump. Most are single-use but some heavy-duty versions handle two or three fills if handled carefully.
For larger dewatering jobs, geotextile filter tubes on the 50 metre roll can be cut to length and used as inline silt traps along a pump line or check dam across a drainage channel.
Sand bags are the other product that gets called a silt bag on Australian sites. They are woven fabric bags filled with sand, used to build quick barriers around drains, along site boundaries and at flow concentration points. Properly stacked, a sand bag wall slows water enough for sediment to drop out before the water moves on.
The three common materials each have a place. Hessian breathes and decomposes, which suits short-term jobs.
Poly is waterproof and UV-stable for longer exposure. Premium green poly handles the longest outdoor life, especially on sites that get repeated rain events.
| Material | UV life | Water resistance | Best for |
|---|---|---|---|
| Hessian | 3 to 6 months | Absorbs water, breathes | Short-term fill, flood response, garden use |
| Poly (white) | 6 to 12 months | Waterproof weave | Medium-term site work, drain protection |
| Premium green poly | 12 to 24 months | Waterproof, UV stable | Long-running sites, permanent bunds |
All Stake Supply keeps all three options in stock at the St Marys warehouse, with hessian sandbags in 50 packs for small jobs and premium green sandbags in 1,000 packs for larger civil projects.
Silt bags and silt fences solve the same problem from different angles. A silt fence is a permeable fabric barrier fixed to stakes, running along the low side of a disturbed area.
Silt bags sit at flow concentration points, drain inlets and pump outlets. Most sites need both.
A silt fence catches sheet flow across a slope. Silt bags deal with concentrated flow that has already been channelled (a pipe outlet, a swale, a driveway edge). Trying to use one where the other belongs is how sediment ends up off-site.
For the fence side of the job, the range of standard green silt fence in 100m rolls covers most residential and commercial sites. Read more on what silt fencing does and how to install a silt fence if fence work is new to the crew.
A sand bag barrier only works if it is built right. Loose stacking lets water find gaps, and overly dense packing stops water moving through and pushes it sideways.
The aim is a stable wall that slows flow without dramatic ponding.
Common mistake: Packing bags too hard. An overfilled bag behaves like a log, while a two-thirds fill bends around its neighbour and actually seals the wall. Most leaks on a sand bag barrier come from bags filled too tight, not too loose.
See how to fight flooding with sandbags for a walk-through of barrier heights and positioning during wet weather events.
Almost every council in Australia requires an erosion and sediment control plan for construction work that disturbs more than a small area. Silt bags appear in those plans as a compliance tool, often alongside silt fencing, stabilised access points and sediment ponds.
State environmental agencies back up council requirements. The Australian Department of the Environment sets national guidance on waterway protection, and most state EPAs publish erosion and sediment control handbooks that specify where filter bags and sand bags belong on a site layout. The NSW EPA stormwater guidance is a useful reference for landscapers and civil contractors working across New South Wales.
The right bag depends on three things: what problem the bag is solving, how long it needs to sit on site, and the volume needed. A small residential landscape job and a major civil project do not need the same product.
A poly sandbag 50 pack handles most small jobs. Light enough to carry, quick to fill, and lasts long enough for a typical two-to-four week residential build.
A premium green sandbag 50 pack suits a site that will stay open for two to six months. The UV stability matters once a bag has been exposed to a full summer.
For major works, premium green sandbags in 1,000 packs are the most cost-effective option. Ordering in bulk also removes the risk of a partial delivery stopping site work when an inspection is due.
For check structures in drainage channels, hay bale bags filled with straw or rice hulls work as natural check dams that trap sediment while letting filtered water pass.
The selection below covers the main silt bag types stocked for Australian sites, from short-term hessian through to long-life premium green poly. Ordering everything from one supplier keeps a sediment control plan tidy and avoids the partial-delivery problem that stalls inspections.
The full sandbag range has all pack sizes, and the broader sediment control category covers silt fence, coir logs, and geotextile filter products. All Stake Supply ships complete orders anywhere in Australia, guaranteed complete and on time.
Silt bags are a small part of a sediment control plan with a big effect on whether a site passes inspection. Pick the right material for how long the site will be open, fill bags two-thirds for stable walls, and match filter bags to the pump rate when dewatering.
Most jobs use a mix of filter bags for pumped water, sand bags for perimeter protection, and silt fence for sheet flow. Ordering the whole kit together from one supplier is faster, cheaper and avoids waiting on a missing item when the rain is already forecast.
Setting up sediment control on a new job? Browse the full range at All Stake Supply or contact the team for trade pricing and bulk orders.
