Sandustry Filter Guide: Allow vs Block, Jams & Sorting

Allow vs Block

A standard Filter acts like a Conveyor Belt with a downward outlet.

Allow
Select one material that is allowed to fall through. Other material continues along the belt.

Block
Select one material that must stay on the belt. Other eligible material falls through.

The current Official Wiki says a standard Filter:

• filters one material type;
• does not block liquids;
• does not block gases;
• blocks the player under normal movement.

Advanced Filters are a separate later unlock and can handle additional material types, including fluids.

What v0.5.7 Changed

Update #4 fixed two Filter-related issues that are easy to confuse with normal mechanics.

Pass-Through Filter Bug Fixed

The v0.5.7 changelog says a bug that could create a pass-through Filter by picking a Filter Wall was fixed.

If an old setup depended on that accidental behavior, do not treat it as a supported Filter mode.

Lava No Longer Leaks Through Advanced Filter Walls

v0.5.7 also fixed Lava leaking through Advanced Filter Walls.

This does not change the ordinary standard Filter rule. Standard Filters still do not block liquids, and the deliberate Cinder/Lava burner setup documented below still uses the standard Filter body with a blocked exit.

Why Is My Filter Jammed?

Check these causes in order.

1. The Output Below Is Blocked

If a solid block or a packed pile closes the space below the Filter, material can enter without having somewhere to leave.

This behavior is useful intentionally for trapping Cinder/Lava, but it is a jam when you expected normal sorting.

2. A Material Changed Inside the Filter

The Official Wiki explicitly documents this failure mode.

If an allowed pixel changes into a different material while passing through the Filter, the new material can become stuck.

Common examples:

• Sand + Water → Wet Sand
• Seed + Water → Wet Seed

Because standard Filters allow Water through, a sorting line that mixes Water with dry Sand or Seed can create a reaction jam inside the Filter body.

Move reaction/wetting steps away from the sorting surface when possible.

3. Density Is Preventing the Right Material from Reaching the Filter

Tall mixed piles separate by density.

A lighter material can sit above a denser layer and fail to reach the Filter even when the rule is correct. The current Wiki says Filters can pull material from roughly 1 block / 4 pixels away through denser material, but also warns that this is not completely reliable.

Use shallow, controlled feed layers rather than assuming a deep pile will sort perfectly.

4. The Rule Is the Opposite of What You Intended

If a line behaves backward, confirm whether you selected Allow or Block.

The official v0.5.4 update improved Filter editing:

• the overlay label / “Edit last placed” can be used to change a Filter more quickly;
• Allow and Block were given clearer visual distinction.

Those UI improvements remain relevant in v0.5.7.

A Reliable Troubleshooting Order

1. Clear the lower output.
2. Inspect the actual material touching the Filter.
3. Remove Water or other reactants from the sorting point.
4. Reduce the depth of mixed input piles.
5. Confirm Allow vs Block.
6. Check whether the setup depended on an old pass-through Filter bug.
7. Re-test with a small known batch before scaling the line.

Lava Holding in a Standard Filter

The Official Wiki documents a deliberate use of the blocked-output behavior:

1. set a Filter to allow Cinder;
2. place a solid block below;
3. fill the Filter with Cinder;
4. ignite the Cinder to create trapped Lava.

That is a special-purpose burner layout, not a normal sorting configuration.

The v0.5.7 Advanced Filter Wall leakage fix should not be read as a change to this standard Filter technique.

Related Sandustry guides

• Wet Seed automation
• Move Lava
• Production recipes