One of the most common questions our sales team receives is: What’s the difference between cast iron covers that are “cast in” and those that are “supplied loose”? Here’s a simple explanation – and how to choose the right option for the installation of your grease arrester, rainwater tank or vertical septic tank.
What does “cast in” mean?
“Cast in” means the cast iron cover is set directly into the concrete lid or ring of your tank during manufacture. This approach is most common when the tank is located in a garden bed, gravel area, or other landscaped space.
The main benefits are:
- Security: The cover is fixed in place and can’t be moved by people or vehicles.
- Durability: It’s better protected from impacts.
- Neat finish: Once landscaping is complete, only the cast iron is visible for a clean, professional look.
Example:
The photo below shows cast iron covers cast into concrete rings for a tank installed in a garden bed. Once landscaping is complete, the result is stable, durable, and visually seamless.
In this next example, you can see a completed landscaped or lay-down area with the cast iron covers cast in, creating a neat, clean finish that vehicles cannot move or dislodge.
What does “supplied loose” mean?
“Supplied loose” means the cast iron cover is provided separately and placed on top of the tank lid during or after installation – not fixed in place. This is usually preferred when the final surface will be concrete, bitumen, or paving.
The main benefits are:
- Flexibility: You can adjust the cover’s position to match the final surface level or slope.
- Better integration: Concrete or bitumen can be poured right up to the edge of the cover, so the tank lid isn’t exposed.
- Easy access: Covers can be removed if needed for maintenance.
Example:
Here, a loose-supplied cast iron grate that sits on a rainwater tank before a driveway is poured. Because it’s loose, the installer can easily raise or tilt the grate to match the gradient and ensure stormwater flows directly into the tank.
Common mistakes to avoid
Getting the levels wrong during installation can create issues later.
Example:
The example below shows a loose cover sitting too high after the bitumen was laid – a costly and difficult mistake to fix.
Example:
Similarly, while cast-in covers can look tidy next to paving like the example below, the finish is cleaner if the pavers extend over the tank lid and only the cast iron is exposed.
Our advice
After many years of supplying our products, we’ve found that cast iron covers are most often supplied loose, but the right choice ultimately depends on where the tank is installed and the type of surface finish around it. If the tank will be located in a garden bed or gravel area, casting the covers into the concrete lids or rings is usually best, as it prevents them from being moved by people or vehicles. However, if the finished surface will be bitumen, paving, or concrete, supplying the covers loose allows you to pour right up to the edge, avoid exposing the tank lid, and easily adjust the level – even raising or tilting the cover with risers or bricks if needed – to suit the final surface.
Whichever option you choose, it won’t affect how your septic tank, rainwater tank, or grease arrester functions. It’s purely about achieving the most practical, secure, and visually neat finish.
If you’re unsure which option is right for your project, contact our sales team on 8444 8100 to help you choose the best solution when you place your order.
Ri-Industries is pleased to announce our new Ri-Treat product called the 
