The old litter was discontinued, or the new one was on offer, or a review said it was better for the environment. You emptied the tray, filled it with the new stuff, and within two days there was a puddle on the bath mat.
This is not protest and it is not spite. The 2014 AAFP and ISFM house-soiling guidelines put it plainly: the behaviour “is not due to spite or anger toward the caregiver, but because the cat’s physical, social, or medical needs are not being met.” You changed the one surface in the house she is willing to dig in, and she has gone looking for another one. Bath mats, rugs and piles of laundry are all closer to what she wants than a tray full of pellets.
The fix is straightforward, as long as you do it in the right order and do not spend three weeks waiting for her to get used to it. She will not.
The short version
- Put the old litter back today, in the same tray, in the same place. Do not wait it out.
- If she is urinating outside the tray and there is any straining, blood, or frequent small amounts, stop and ring a vet. Urinary blockage is an emergency in male cats.
- Cats have real substrate preferences and they are measurable. In a field study comparing clay, silica and wood pellets, cats significantly preferred clay or silica over wood pellets.
- Fine, sand-like, unscented material is what most cats choose. A 2025 preference test found scent was not a factor, which is worth knowing given how much scented litter is sold.
- When you do switch, do it by mixing: a small proportion of new litter into the old, increased over two to four weeks, and back a step at the first accident.
- Never change litter, tray and location at the same time.
On this page
First: is this a medical problem?
The timing looks obvious, but do not let it stop you checking. Cystitis, urinary crystals and other urinary problems often appear at the same time as a household change, because stress is part of the picture, and a cat who associates the tray with pain will avoid it regardless of what is in it.
Ring a vet the same day if you see any of these: straining in the tray with little or nothing produced, crying while urinating, blood in the urine, repeated visits to the tray in a short period, or excessive licking underneath. In a male cat, straining with nothing produced is a urinary blockage, which is a life threatening emergency and needs a vet immediately, not in the morning.
Also worth a vet call, though not urgently, if your cat is older and has started missing the tray or having accidents: arthritis makes climbing into a high-sided tray painful, and that can look exactly like a litter complaint.
Why the new litter failed
Digging substrate is not a matter of taste for cats in the way a food flavour is. Kittens learn what they bury in early and the preference sticks, and an adult cat asked to switch to something with a different feel underfoot often just declines.
The usual culprits, in order of how often they cause this:
| What changed | Why it matters to her |
|---|---|
| Fine grains to pellets | The biggest jump of all. Wood, paper and tofu pellets feel nothing like the sand she grew up with, and they do not cover waste the way she expects. |
| Unscented to scented | Perfume is added for humans. A cat’s nose is in the tray while she digs. |
| Dust and texture | Some crystal and silica litters feel sharp or cold underfoot, especially for a cat with sore paws or after a claw trim. |
| Depth | A thin layer over hard plastic gives her nothing to dig into. Cats who cannot dig properly often stop using the tray. |
| Everything at once | New litter plus new tray plus a new spot is three changes. Any one of them can be the dealbreaker, and you cannot tell which. |
What cats actually prefer, according to the research
This is not guesswork, and the findings are consistent enough to be useful when you stand in the shop.
Villeneuve-Beugnet and Beugnet ran a field assessment published in the Journal of Veterinary Behavior in 2018, comparing clay granules, silica and wood pellets across two phases with 18 and then 12 cats. Their result: “the cats demonstrated a significant preference for the clay or silicate substrates (no significant difference between them) as opposed to the wood pellets.” When they compared substrates of the same grain size, the cats still preferred to defecate in clay.
A more recent preference test by Cassiday and Cassiday, published in the IAABC Foundation Journal in 2025, offered nine cats a choice between seven alternative substrates and their familiar clay. Of 201 deposits recorded, 148 were in the clay. The authors also concluded that “scent is not a factor for litter preference”.
Two caveats worth keeping in mind, because the authors state them. The sample sizes are small, and every cat in these studies had a learning history with clay already, which loads the dice. What the research does support is simple: fine, sandy, unscented material is the safe default, and pellets are the riskiest switch you can make.
If you are switching for environmental or dust reasons, which are legitimate, the finest grained version of the alternative material gives you the best chance. Pellets that break down into sawdust when wet are a closer match than pellets that stay whole.
Undoing it, this week
- Put the old litter back. Today, not at the weekend. Every day she uses the bath mat, the bath mat becomes more of a habit and more of a scent marker, and you end up solving two problems instead of one.
- Add a second tray with the old litter, if you have space. This gives her an obvious correct option near where the accidents happened, and you can remove it later.
- Clean the accident spots properly. An enzymatic cleaner, not a general household cleaner. Anything containing ammonia smells like urine to a cat and invites a repeat. Do not use bleach on the spot for the same reason.
- Make the accident spot uninteresting. Take the bath mat up for a while. Put a litter tray there temporarily if the spot is a favourite, then move it a few centimetres a day back to where you want it.
- Do not tell her off. Punishment after the fact teaches her to avoid you, not to use the tray, and it adds stress, which makes urinary problems more likely.
- Wait for a fortnight of clean behaviour before you try anything new. Reliability first, experiments afterwards.
How to switch litter properly next time
There is one rule: she should not notice it happening. Mix, do not swap.
| Stage | Mix | Hold for |
|---|---|---|
| 1 | Roughly a quarter new, three quarters old | 3 to 5 days of normal use |
| 2 | Half and half | 3 to 5 days |
| 3 | Three quarters new | 3 to 5 days |
| 4 | All new | Watch closely for a week |
That is two to four weeks for a full switch. If at any stage she hesitates, scratches at the floor outside the tray, perches on the edge rather than standing in it, or has one accident, go back to the previous mix and stay there for a week before trying again. Those hesitations are the warning, and they come before the puddle.
The safer version of this, if you have the room: put the new litter in a second tray next to the current one and let her choose. You will know her answer within a couple of days, and nothing is at risk while you find out. This is also the only reliable way to test whether the problem is the litter at all.
If she still will not use it
If the old litter is back and the accidents continue, the litter was not the whole story. Work through these, one at a time.
Tray count. The standard guidance is one tray per cat plus one spare, in different locations. Two trays side by side count as one location to a cat.
Cleanliness. Scoop at least once a day, more with several cats. Cats are cleaner than the schedule most of us keep.
The cleaner you use on the tray. Strong disinfectants leave a smell she can detect long after you cannot. Hot water and a mild unscented detergent is enough.
Location. Next to a washing machine that starts mid-visit, in a busy hallway, or in a corner where another cat can trap her. Trays need an escape route and quiet.
The tray itself. Too small, sides too high for an older cat, or a hood she dislikes. Our comparison of covered and uncovered litter boxes goes through what the evidence says about hoods.
Another cat. In a multi-cat house, one cat guarding the route to the tray is a common hidden cause. Look at who walks past whom, not just at who used the mat.
Stress. A move, building work, a new baby or a cat outside the window can all show up as house soiling. The AAFP and ISFM guidelines pair tray optimisation with meeting the five pillars of a cat’s environmental needs for exactly this reason.
If none of this shifts it within a few weeks, go back to your vet and ask about a referral to a qualified cat behaviourist. Persistent house soiling is one of the most common reasons cats are rehomed, and it is usually fixable with the right help.
Common questions
I changed my cat’s litter and now she will not use the box. What do I do?
Put the old litter back straight away rather than waiting for her to adjust, clean the accident spots with an enzymatic cleaner, and check with a vet if there is any straining, blood or repeated visits to the tray. Once she has been reliable for a fortnight, switch again slowly by mixing the new litter into the old over two to four weeks.
How long does it take a cat to get used to new litter?
If you switch gradually, two to four weeks. If you switch all at once, many cats never accept it, and waiting it out usually just establishes a new toileting spot elsewhere in the house.
What litter do cats prefer?
The research points to fine, sandy, unscented material. A 2018 field assessment found a significant preference for clay or silica over wood pellets, and a 2025 preference test found cats chose their familiar clay for 148 of 201 deposits when offered seven alternatives, with scent not a factor.
Is scented litter bad?
It is not harmful, but it is added for people rather than cats, and the 2025 preference test concluded scent was not a factor in what cats chose. Some cats clearly dislike it, so unscented is the safer default.
Can I just mix the new litter in and hope?
Mixing is the correct method, but not in one go. Start with roughly a quarter new, hold for several days of normal use, then increase. Go back a stage at the first hesitation or accident.
Should I punish my cat for going outside the tray?
No. The AAFP and ISFM guidelines state that house soiling is not about spite, it happens when a cat’s physical, social or medical needs are not met. Telling her off adds stress and teaches her to avoid you, not to use the tray.
Why does she keep going back to the same spot?
Because it still smells like a toilet to her, even after normal cleaning. Use an enzymatic cleaner, avoid anything containing ammonia, and make the spot physically unavailable or uninteresting for a few weeks.
The bottom line
She is not making a point. You changed the digging surface, and the one she had was the one she agreed to. Put the old litter back today, rule out a urinary problem if anything about her toileting looks painful or frequent, and clean the accident spots with an enzymatic cleaner. Then, if you still want to change litter, do it by mixing a quarter at a time over two to four weeks, and treat the first hesitation as the answer rather than waiting for the puddle.
Sources
- Villeneuve-Beugnet V, Beugnet F. Field assessment of cats’ litter box substrate preferences. Journal of Veterinary Behavior, 2018;25:65-70. Significant preference for clay or silica over wood pellets.
- Cassiday L, Cassiday C. Evaluating litter substrate preference in a population of cats. IAABC Foundation Journal, 2025, issue 31. Nine cats, 201 deposits, 148 in clay; scent not a factor.
- American Association of Feline Practitioners and International Society of Feline Medicine. Guidelines for diagnosing and solving house-soiling behavior in cats, 2014. House soiling is not spite, and management centres on optimising the tray and meeting the five pillars of environmental needs.
