Why Cat Litter Sticks to the Bottom of the Box
Litter welds itself to the floor of the box when urine gets past it. That happens for one of five reasons, and four of them are free to fix. Only the fifth, a litter whose clumps fall apart before you can lift them, needs you to buy something different.
The clump figures on this page come from our own drop test: a fresh clump is lifted and dropped from three feet, and we record whether it survives whole.
Check these five, in this order
Start at the top. Each one is cheaper to rule out than the one below it.
- 1
The clump broke before you got to it
How you know: The stuck patch is flat, wide and pale, and it sits right under where your cat squats.
A clump that falls apart on the way to the scoop leaves wet litter on the floor of the box, and wet clay sets like grout. This is the cause most of the time, and the only real fix is a litter that holds together.
- 2
The bed is too shallow
How you know: You can see plastic through the litter in places, usually in one corner.
Urine has to be caught before it reaches the bottom. Under an inch of litter and it will not be. Top the box up to a level bed rather than adding a heap in the middle.
- 3
You are scooping too late
How you know: The box is fine on the days you scoop in the morning and cemented on the days you skip.
Most clumping litter firms up over a few hours and then starts to soften again as it dries and gets walked on. Scooping once a day catches clumps while they are still liftable.
- 4
The plastic is scratched
How you know: The same two or three spots stick every single time, and the box is more than a year or two old.
Scoop edges cut grooves into the floor of the box, and litter packs into the grooves. No litter fixes a worn box. Replace it, or line it.
- 5
The room is damp
How you know: It only happens in the basement, the laundry room or in summer.
Clumping clay pulls moisture out of the air as happily as out of urine. A box in a damp room sets at the bottom on its own. Move it, or run the extractor fan.
The clump numbers behind cause one
We drop a fresh clump from three feet onto a hard surface and record whether it comes through in one piece. A litter near the bottom of this list is leaving wet grit in the box every time you scoop, and that grit is what sets.
| Litter | Clumps that survived | What that means at the box |
|---|---|---|
| Dr. Elsey's Cat Attract | 98% | Lifts clean. Sticking here is almost always the box, not the litter. |
| Dr. Elsey's Ultra | 98% | Lifts clean. Sticking here is almost always the box, not the litter. |
| Boxiecat Premium | 94% | Lifts clean. Sticking here is almost always the box, not the litter. |
| Naturally Fresh Walnut | 89% | Mostly holds. Expect the odd crumbled clump if you scoop late. |
| Arm & Hammer HardBall | 87% | Mostly holds. Expect the odd crumbled clump if you scoop late. |
| Tuft + Paw | 78% | Mostly holds. Expect the odd crumbled clump if you scoop late. |
| World's Best Cat Litter | 76% | Mostly holds. Expect the odd crumbled clump if you scoop late. |
| Catalyst Soft Wood | 73% | Crumbles often. Wet grit gets left behind and that is what cements. |
| Fresh Step Scented | 66% | Crumbles often. Wet grit gets left behind and that is what cements. |
| Arm & Hammer Super Scoop | 64% | Crumbles often. Wet grit gets left behind and that is what cements. |
| Purina Tidy Cats | 62% | Crumbles often. Wet grit gets left behind and that is what cements. |
| Frisco by Chewy | 58% | Crumbles often. Wet grit gets left behind and that is what cements. |
Litters with no figure here are non-clumping by design, such as pellets and crystals. They do not form clumps to break, and they handle urine a different way.
Getting the stuck layer out today
Do not attack it dry. Dry scraping is what puts the grooves in the plastic that make the next patch worse.
- Tip out the loose litter first, so you are not soaking a full box.
- Pour in an inch of hot water and leave it for 20 minutes.
- Lift the softened sheet with a plastic putty knife or an old plastic scoop.
- Rinse, dry the box fully, then refill. A damp box starts the cycle again.
- If two or three spots come back every time, the plastic is worn out. Replace the box.
If it is the litter, what to move to
Hard-clumping clay is the category built for this. Dr. Elsey's Cat Attract led our drop test at 98%, and clumps that strong come out whole even when you leave them a day. If you would rather stay off clay, a pellet litter sidesteps the problem entirely, because nothing is trying to clump in the first place.
Questions people ask
- Why does cat litter cement to the bottom of the box?
- Urine that reaches the floor of the box before the litter can absorb it dries into a hard sheet. That happens when a clump breaks apart, when the bed is too shallow, or when the box sits somewhere damp.
- How do I get stuck litter off without wrecking the box?
- Pour in an inch of hot water, leave it 20 minutes, then lift the softened layer with a plastic scraper. Metal scrapers cut grooves into the plastic and those grooves make the next patch stick harder.
- Does a liner stop litter sticking?
- It stops it welding to the plastic, which saves the box. It does not stop the sheet forming, and many cats shred liners while they dig, which puts urine underneath the liner instead.
- Which litters hold their clumps best in your testing?
- Dr. Elsey's Cat Attract came out on top of our drop test at 98% of clumps surviving intact. The weakest we have tested, Frisco by Chewy, survived at 58%.