Pre-mixed cement and aggregate, dried and sealed in a 25kg hessian bag. Place, wet, and walk away. The concrete sets to form a solid, permanent structure and the hessian breaks down naturally, leaving no residue.
Supplied by Bag Boys. Bulk pricing available for trade, farm and civil contractors.
What they are
Culvert bags are a pre-mixed cement and aggregate product, dried and bagged at 25kg. They are designed to be laid like bricks around culvert inlets and outlets, alongside drainage infrastructure, or wherever you need a fast, formed concrete structure without mixing or formwork.
Once placed and wetted (either by rain or by hand) the mix sets to solid concrete. The bag itself degrades over time, leaving a clean, durable structure.
How to use them
- Stack bags around the culvert inlet, outlet, or area requiring protection, layered like brickwork
- Secure with waratahs, basalt rock, or rebar as needed
- Wet thoroughly, or leave for rainfall to do the work
- Allow to set - initial set within hours, full cure over 28 days
No mixing. No formwork. No concrete truck.
Why hessian
We use hessian for a deliberate reason. These bags go near water - culvert crossings, farm drains, waterways, stormwater infrastructure. Other options like woven polypropylene (or plastic LDPE) do not biodegrade and they photo-degrade, fragmenting into microplastics. For a bag placed at a waterway or drainage structure, that means microplastics going directly into the water the bag is supposed to be protecting.
Hessian is a natural jute fibre. It breaks down completely with no residue, no microplastics, and no environmental liability. For any application near water, it is the right material.
We do not offer woven polypropylene or plastic LDPE in this product for this reason.
Common applications
- Culvert inlet and outlet protection
- Farm track and gateway crossings
- Road drainage stabilisation
- Waterway and stream bank protection
- Scour control beneath bridges and culverts
- Retaining structures for earthwork slippage
- Erosion control on steeper grades where structure is needed
Supplied from Waikato. Available in full pallet quantities. Contact us for bulk pricing and lead times.
Specifications
| Detail | Spec |
|---|---|
| Weight | 25kg per bag |
| Filled dimensions | 400 x 300 x 100mm (approx) |
| Bag material | Natural hessian (jute) |
| Fill | Pre-dried cement and aggregate mix |
| Coverage | Approximately 17-19 bags per m2 |
| Cure time | Initial set within hours; full strength at 28 days |
| Bags per pallet | 40 |
| Supply | Full pallets; bulk pricing available |
| Origin | Filled at Hamilton, Waikato |
FAQ Section
What's the difference between your culvert bags and concrete culvert bags from merchants? Same product, different bag. Other suppliers culvert bags use a paper bag with a similar cement and aggregate mix. Paper and hessian both biodegrade cleanly and either works well near waterways. We use hessian because it handles moisture better during installation and is more forgiving in wet or damp site conditions.
What about woven polypropylene culvert bags? We do not offer them. Woven polypropylene does not biodegrade - in New Zealand's UV conditions it fragments into microplastics. For bags placed at waterways and drainage structures, we do not think that is an acceptable trade-off. Hessian does the same job and leaves nothing behind.
Are these the same as compost or seed-filled erosion control bags? No. Compost socks, silt socks, and coir logs are filled with organic material and are designed for embankment revegetation. The fill retains moisture and seed germinates through the mesh over time. Our culvert bags are a cement and aggregate product that sets to permanent concrete. Different application, different result.
Can I use these on a steep bank or slip-prone area? Yes. Culvert bags work well for earthwork retaining where a heavier structure is needed. For very steep or high-load areas, consult your engineer, but as a first-line retaining measure they are well suited to slips, eroding banks, and drainage channels.
Do you supply to farms and rural contractors? Yes. Most of our culvert bag orders are B2B - farm supplies, rural contractors, and civil contractors. We can quote per pallet or per project. Contact us at tradesales@bagboys.co.nz
How many bags do I need? As a guide, approximately 17-19 bags covers one square metre. For culvert inlet and outlet work, most standard residential or farm culverts require between 20 and 60 bags depending on pipe size and depth of scour protection needed.