Sandustry Filter: Wet Sand and Water Guide

Here is the answer most players actually need: a Sandustry filter checks only the single tile directly above it — one block above — and it never blocks water. To pass Wet Sand while holding back Water, you pair two different parts: solid blocks or normal conveyor belts form the waterproof floor (belts block liquids, even though water ignores their travel direction), and a filter set to "allow only wet sand" sorts the slush. Then you narrow the channel so the material column over each filter tile is exactly one pixel deep — any deeper and buried pieces slip through unchecked. Wet sand is a slushy solid that rides this geometry; water is a liquid that ignores the Sandustry filter entirely.

What a filter is

Filters arrive early in the logistics research — recorded Early Access runs unlock them right after the first shaker line works — and do exactly two jobs, chosen in a small popup when you place them:

• Allow only the selected element — one chosen pixel type passes; everything else is held.
• Block the selected element — the chosen type is held; everything else passes.

A placed Sandustry filter also shows an arrow: like a conveyor belt, it nudges material in that direction. Players exploit this constantly — a filter row is simultaneously a sorter and a slow belt. Official documentation describes the behavior as type-based pass/block, which is worth remembering when fan sites talk about "density bands": those charts are unofficial community framing, not how the machine decides anything. A Sandustry filter never weighs or measures a stream — it pattern-matches one pixel type on one tile.

The one-block rule, and the bottleneck that fixes it

The mechanic that makes or breaks every Sandustry filter line: only the pixel sitting one block above the filter face is evaluated. Demonstrations of this are unambiguous — drop a tall mixed pile on a filter and the top layers pass unsorted, because the filter never "sees" them. The working fix is geometry, not more filters:

This is also why a Sandustry filter placed under a deep storage box appears to "not work": it is checking one tile of a fifty-tile pile. Mechanics videos show a second flavor of the same trick — a filter mounted on a shaker's output, set to pass only slag, holds wet sand on the grate until it converts, which keeps half-processed material out of the slag lane.

Wet sand versus water, specifically

The common factory question — "my filter lets wet sand through but water follows it" — dissolves once you separate containment from sorting:

• Containment: build the water channel's floor and walls from normal conveyor belts or solid blocks. The official water entry confirms water passes through most blocks, filters included — belts are the exception that holds liquid.
• Sorting: keep the wetting zone shallow so wet sand never hangs suspended in a deep pool, let gravity carry it toward the shaker input, and only then put a configured filter in its path to strip out stragglers like dry sand or slag.

Never assign a Sandustry filter the job of being a waterproof wall. It will fail silently and flood your shakers. Water resting on a belt does not travel in the belt's direction either, so a belt floor contains water without moving it — route deliberate overflow with pipes and vents once fluid research lands.

Filters as flow regulators

Because a filter trickles material through at a measured pace — much slower than an open belt or a launcher dump — experienced players use single-material Sandustry filter rows as pacing devices:

• Before shakers and presses: a filter roof meters the stream so machines receive a trickle they can actually process. This is the standard anti-jam step in the Kinetic Press guide.
• Sort in series, not in parallel: regulate the flow first, then run several filters in a row, each dropping out one unwanted material. A short, well-paced series beats a wide bank fed by an overloaded launcher.
• Cap belt loads around two tiles high so no belt can deliver a deep slug all at once.
• Throttle launcher force feeding any sorting line — maximum power delivers material faster than a Sandustry filter can evaluate it, and everything arrives as one mixed slug.

Mixed streams, backflow, and recirculation

Real mines never deliver clean single-material belts, so the practical Sandustry filter craft is mostly about what happens around the machine:

• Give every stream a home. Unclaimed material should never dribble into a corner — close the belt line into a loop so leftovers ride back to the start for another pass. Recorded Early Access builds swear by this cycle, because a looping stream cannot silently pile up somewhere you forgot to look.
• Merge lanes only after the last filter stage. A merge between stages re-mixes what you just separated and makes the next filter's job impossible.
• Test before you trust. Route a new filter's output into a temporary box and watch it for a minute; the wrong material in the box means the mode or element is mis-set, and gold in a reject lane means the rule is backwards.
• Label as you build. Pass lane versus reject lane, target material, destination — a screenshot per stage saves you when an expansion branch connects to the wrong side weeks later.

Advanced filters in Early Access

Early Access adds an advanced filter tier, and recorded runs confirm it extends the same pass-or-block logic to liquids and gases — the standard Sandustry filter handles granular solids only. The build players show off most is a lava valve: one advanced filter set to block lava, a second set to block cinder, cinder loaded on top and ignited — the lava stays boxed while its bubbles still rise to burn whatever needs burning. The one-block rule still applies, so narrow liquid channels exactly as you would narrow a sand stream.

When filters fail: the checklist

• Wrong material gets through → the pile above the Sandustry filter is deeper than one tile; add the bottleneck block.
• Nothing gets through → wrong mode or wrong element selected; re-open the popup and check the arrow direction too.
• A pixel jams inside the filter → material can change state mid-passage (wet sand drying back to sand, for instance) and wedge; clear it and re-wet upstream.
• Water everywhere → you asked a filter to do a conveyor belt's job. Rebuild the floor with belts.
• Sorted output re-mixes downstream → merge lanes only after the last filter stage, not between stages.
• Throughput mysteriously halves → a launcher upstream is overpowering the line; throttle it before adding a second Sandustry filter in parallel.

Master those two facts — one tile of vision, no liquid barrier — and the Sandustry filter becomes the cheapest precision instrument in the game: a sorter, a gate, a throttle, and a pump-free valve, all for the price of one early research node.