Rock bags from different makers can look alike and be built very differently. Before a product goes into your specification, ask each manufacturer for the same evidence and compare the answers line by line.
In short: ask what each published figure means, how it was measured, and which documents come with the product. The checklist below works with any supplier, including us.
Checklist: what to ask a rock bag manufacturer
- A data sheet for each size. Dimensions, volume, mesh opening, recommended rock grading and empty weight, in the units your project uses.
- What each rating means. A current rating should say whether it is for a single bag or for bags placed as a group, and what was measured (for example, the velocity at which the bags show no movement).
- The test behind each claim. For every strength, UV or abrasion statement, ask which test method was used and who carried it out. A claim with no method behind it is hard to defend in a submittal.
- Currents or waves. Ask whether the ratings cover currents only, or waves as well. Wave loading needs its own evidence.
- Net, closing rope and lifting ring. What each is made of, and how the ring is joined to the net. The ring carries the full weight of the filled bag on every lift.
- Durability evidence. What the maker can show for exposure to sunlight, abrasion and long periods in water, and for which design life.
- Fill and installation instructions. A written manual for filling, closing, lifting and placing, so that your contractor works to the same method the figures assume.
- Quality control and traceability. How a delivered bag can be traced back to its production batch and the records for that batch.
- References for the same use. Projects with a similar application and similar conditions, with someone you can ask.
- What is supplied. Empty nets, filled bags, filling frames, lifting gear or site support: which of these the maker provides, and which your contractor has to source.
Warning signs
- A velocity rating that does not say single or grouped, or currents or waves
- Strength or durability statements with no test method named
- No written filling and installation instructions
- Figures that differ between the data sheet, the brochure and the website
- Claims that a product suits every site; no erosion product does
Write the checks into the specification
You do not have to name a brand to get these answers. Specify the size, the rating you need and the documents to be submitted, and any maker who meets them can bid. Our specification clause is written that way and lists the submittals a reviewer will ask for.
What EVOSNT provides
Ask us every question on the checklist above, the same as you would ask anyone else.
- We manufacture EVO Rock Bags, so questions about the product come straight to the maker.
- A published size table for the 2, 4 and 8 ton bags: mesh, recommended rock size, height, diameter, volume, empty weight with ring, and current ratings for single and grouped placement. See the specifications.
- Each rating is stated as the flow velocity at which the bags show no movement, placed singly and grouped. The ratings are for currents only; for waves, send the site conditions and we will advise.
- Technical specifications, a Fill and Installation Manual, a Service Life & Durability Summary and a document on windfarms and rock bags, sent on request from the documents list.
Questions
- Can I specify rock bags by performance instead of by brand?
- Yes. State the nominal size, the current velocity the bags must be rated for in single or grouped placement, and the documents to be submitted. Any manufacturer who meets those can bid.
- Why ask how the lifting ring is joined to the net?
- Every lift puts the full weight of the filled bag on the ring and its connection to the net. Ask what they are made of and how the connection is designed and checked.
- Should references be for the same application?
- Ideally, yes. A bag that performs well on a riverbank tells you less about an exposed coast or a quay toe under propeller wash. Ask for projects with similar conditions.
Published by EVOSNT Trading FZCO, manufacturer of EVO Rock Bags. Product figures are from our technical specifications. General guidance only; the project engineer is responsible for the final design.
