Pet urine stains on a hardwood floor © Daniel FriedmanPet Urine Stains & Scuff or Scratch Marks in buildings
A diagnostic guide to identifying & removing urine stains & other marks

  • PET STAINS & MARKS in BUILDINGS - CONTENTS: How to recognize and what to do about scratches or black stains or urine pee and poop marks & smells on indoor walls and trim. This article discusses dog stains on walls, people-stains on walls, urine stains in buildings including urine stains on floors & carpets, and scratches made by pets or other animals in or around buildings. We also give first aid advice for carpets that have been peed-on or pooped-on by pets or other animals.
  • POST a QUESTION or READ FAQs about how to recognize pet stains in building walls & floors; how to remove pet urine stains & odors

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Pet & other animal stain identification in buildings:

This article describes common indoor stains caused by animals and pets on floors and walls due to pet urine or simply from a pet frequently lying against or touching a building surface. We also describe a range of pet scrapes and scratches that can provide evidence about the building history of presence of pets.

These photographs also assist in determining when a building has previously housed pets or other animals even if none are currently present. We discuss the cause and cure of various types of pet stains, scrapes, scratches, and smells.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

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How to recognize black stains on indoor walls and trim caused by pets, not mold

Black indoor stain is dog dirt not mold

Article Contents

Pet (Dog) Stains on the Walls of a Building

With a little thought we can easily distinguish pet stains on drywall from thermal tracking by the stain pattern and location as well as other details such as the absence of a heat source, or the identification of a location where we'd expect a pet to rest.

Similarly we can identify black stains on walls where people's heads rested while sitting on furniture or in bed (see photo link just below).

Black marks on interior walls such as the black "mold suspect stains" shown on the white painted drywall in this photo might be just be where the dog lay on the floor against the wall (stain at floor level in this picture) or in this photographof black stains higher on a wall where people rested their heads in bed.

In buildings where pets are or have been housed, smudge marks on walls and at doors and door trim sometimes mistaken for thermal tracking. Our page top photo is recognizable as animal urine stains on a floor . But what about those dark blob stains close to floor level on the wall and on the baseboard trim in our photo at above-left?

Animal scratches & stains on doors and door jambs © Daniel Friedman

These dark wall stains are not mold, but these marks, along with others (scratches, urine stains) can tell us the history of pet occupancy in a building, information of use when investigating indoor air quality concerns, especially in spaces occupied by asthmatics or people with pet allergies.

Black marks on interior walls such as painted drywall might be just be where the dog lay on the floor against the wall (as shown in this photograph).

Provided the stains are due to simple contact between an animal and a building surface, the cures for dog or cat dirt marks on building walls or trim are simple cleaning or at most, re-painting.

Pet stains on Doors & Door Jambs

You may observe dark greasy stains on door jambs, and sometimes scratches and door trim damage due to pets, usually dogs or cats, where those animals frequently pass by, or stop to scratch themselves at those locations.

Our photo (at above left) it is is pretty obvious that "the dog did this" because of the wear where a pet, probably a dog, scratched fruitlessly at the door begging to be let out.

History of dog attacks on the building (C) InspectApedia

But more subtle dark stains may appear in these locations, from the same cause, but where dog and owner had better cooperation, as pointed-to by our client (photo at left). [Click to enlarge any image at InspectAPedia.]

We welcome more thermal tracking, soot tracking, air bypass leaks, and similar photos of indoor stains as well as text suggestions to expand this detail and would be glad to credit contributors.

Usually soot marks, thermal bridging, or thermal tracking stains appear, if at all, in the building interior locations discussed in the remaining sections of this article.

Pet Urine Stains on Building Walls or Carpets

Perhaps the most griped about indoor stain where pets are or were present is cat or dog pee stains on carpeting.

When a dog, cat, (or in some reported cases humans) has urinated on carpeting we recommend that the wall to wall carpet and carpet padding be replaced. Virtually no cleaning product will be capable of removing all of the molecules that invite your pet to pee (or poop) there again.

Even when carpet cleaners and sanitizers are used and the room smells great and there is no visible stain, the presence of pet pee in carpet backing or carpet padding or even in subflooring below will invite a new visit to this public pet toilet.

Door scratched bare by shut in dog © Daniel Friedman

When you remove carpeting and before replacing it, check the condition of the floor below, and if the pee spot was close to building walls, check for pee-soaked drywall or trim boards too.

The flooring or subflooring below the urinated-on carpet needs to be inspected for stains and penetration of urine as well.

More About Killing Pet Odors vs Removing Pet Urine Odors

There are lots of reasons that animals urinate in buildings, and pet owners know most of them: no access to a litter box, dirty litter box, dog shut indoors too long, dog or cat marking territory, fear, etc.

And as we introduced just above, most pet lovers know well that once-peed-on is again-peed-on in many cases.

Back in the 1970's in our first apartment Wappingers Falls one of our two cats peed and pooped on Harriet's pillow.

Was this the cat that peed on Harriet's pillow? © Daniel Friedman

We were not sure which cat chose Harriet for this special attention. But whoever it was, the damn cat did it again and again. Harriet and Hobbit, one of the possible culprits are shown at left. Finally Harriet (the human in the photo at left) gave me this ultimatum:

Either THEY GO or I GO!

My mother later opined that that was when I made a big mistake. Just sayin'. A pet shut into a room and abandoned may have no choice about where it relieves itself.

Because urine leaves an odor in wood surfaces that is difficult to remove, once an area has been used as a cat or dog toilet, animals are likely to return to that spot to pee on it again. It's trivial to throw out a peed-on pillow, but what do we do about peed-on wood floors?

While special pet deodorizers and cleaners are available to clean and remove pet odors, we find that often the animals will continue to return to the scene of their accident or crime. If the amount of urine was very small, an ounce, one event, covering just a few square inches, it may be possible to clean and seal the subfloor using a lacquer primer/sealer, clear shellac, or another appropriate re-finishing coating.


also URINE ODOR REMOVAL in CLOTHING for detailed advice on how to find and remove pet and other animal or human odors and smells in buildings or from carpets and clothing.

Pet Urine Stains on Building Floors - How to Recognize & Remove Stains in Wood Floors

Pet urine stains on a hardwood floor © Daniel Friedman

Often when an animal has urinated one or more times on a carpeted floor, later removal of the carpeting will disclose dark stains in the wood flooring of a finished floor.

Our photo (left) shows severe urine staining on a hardwood floor of a bedroom outside of a bath. The owner was unaware of the stains until the carpeting was removed.

The white colors in the stained area demonstrate the futility of attempting to remove the animal stains by bleach.

If stains penetrate only a millimeter of wood it might be possible to sand and re-finish the floor, or to use a combination of sanding, bleaching, and re-staining of the finish floor as we describe just below.

Reader J.W. comments on using hydrogen peroxide to remove pet urine stains from wood flooring: :

If you have pet urine on blond wood or soft light wood, then you can use hydrogen peroxide on the wood by applying several applications--just rub it in with a cloth or a brand new dry sponge and let dry then repeat often until your wood is light again. I had this problem when i pulled up a carpet that came with the house when i bought it 10 yrs ago & found dark pet stains on the soft yellow pine wood & realized it was pet urine.

We also have removed small areas of stains in wood flooring by working meticulously with diluted bleach and a cotton swab, applying bleach, then washing it off, in several cycles until the stained area of the wood reached a color closely matching the original wood flooring out of the stain.

Watch out: don't over-bleach flooring when trying to remove stains or you'll end up with a too-light area of wood. If you make this mistake, working carefully with wood stain products such as those made by MinWax you may be able to return the over-bleached wood floor area back to the necessary hue. Hydrogen peroxide is less risky in this regard.

But often we find that the urine stains have penetrated the wood so deeply that flooring replacement is about the only option if the occupants don't want to live with these stains.

First Aid for Pet Peed-on Carpets & Hardwood Floors

Blotchy rounded carpet stain © Daniel Friedman

Reader Question: can we see dog pee or poop stains when dry? How do I protect the floors from damage? What will I find under the rug?

I had a few questions about stains on rugs and hard wood floors if you could help me. Can pet stains from a dog be seen when they are dried? Or is there a special way to see them.

Also if pains [sic] stain are on a run and there is a padding underneath the rug will it mess the hard wood floors up? If so how long will it take to mess them up?

Also if the hardwood floor gets messed up from pet stains can it be sanded and refinished?

When a rug is pulled up underneath what would be like dark yellowish stain on the bottom of the rug? - B.M. 01/29/2014

Reply: suggestions for finding animal or other urine stains on carpets & other building surfaces

Pet urine stains on a hardwood floor © Daniel Friedman

In the article above and in companion articles listed at the end (More Reading) we discuss both obviously visible pet urine (or worse) stains in buildings, carpets, floors, walls, and
at UV LIGHT BLACK LIGHT USES we discuss using a black light that can help spot urine stained materials even after drying and where there is no obvious visible mark.

You might also want to check out

The ugly black blotches shown in our photo penetrate rather deeply into this oak hardwood floor. Previously wall-to-wall carpeting had been peed-on repeatedly but the carpet, left in place, hid more difficult damage that was developing in the floor itself.

Deep stains like these may not be removed by surface-sanding, though I have had some success with sanding to remove the top coating of floor sealer, meticulous bleaching, followed by a re-staining and re-finishing of the entire floor.

It may be possible to clean and deodorize carpets but in my experience unless we also deliberately odorize the carpet with something the animal's nose and the animal itself hate (like an ammonia smell) the dog or cat is likely to pee or poop in the same spot again.

It is more difficult to deodorize padding. I would prefer to remove both carpet and padding if peed-on, but understanding that's often very costly and people wish to avoid that expense, one might try carpet cleaning and under-padding replacement.

In my experience animal urine that soaks through carpet and padding and left alone will ruin a hardwood floor by making dark stains that go rather deep into the wood.

A first aid routine that minimizes risk of that damage includes these steps:

Reader Question: odd stains on carpet may be traced to old pet urine spots

9 Oct 2014 Brennan said:

Have you ever seen this in carpet in the middle of a room (not near the baseboards). I received a moisture meter to check some ceiling stains to see if they were active or inactive after the former owner replaced the roof. I was using the moisture meter to check the basement- all surfaces. I found some areas in the basement carpet where the moisture meter was high but dry to the touch. I run a humidifier in that room and it doesn't work very hard to maintain 45-50 rh%

It has a 'line' type stain. A bit darkened (carpet is grey, so this is darkish grey), but not like the other areas where there is actual infiltration soiling (I have seen it is one room near the baseboards but is completely dry). My home is old, so of course it has air leaks.

The former owners had a couch over this area, so I thought it was due to that. Adjacent staining is yellow coloring and also shows moisture in the meter. So moisture and a line/ghosting in carpet. The carpet is gross anyway, so I thought about peeling it back to see if there is a crack in the slab (60+ yr old house). A contractor friend, without seeing it, said it was radon gas escaping. That seemed like a stretch, since Radon is colorless. I think though, perhaps he meant, air is feeding through the crack and depositing soil on the carpet.

If I do find a crack- should is seal it with concrete/caulk and re-carpet and be vigilant about dehumidification?

This question was originally posted

Reply: moisture meters versus carpet stains


A couple of points to consider:

Most moisture meters, if we exclude thermal imaging, rely on measuring differences in electrical resistance to detect moisture. But other contaminants or materials can also decrease resistance in an area of building material. So not every reading variation is necessarily truly detecting moisture. Some attention, particularly looking for possible moisture sources, are key.

Both pin type moisture meters (Delmhorst for example) and electronic moisture meters (such as some Tramex meters) can be fooled by metal nearby: pipes, foil faced insulation, wiring.

Second: no moisture meter, nor thermal imaging device, can detect old leaks that have since dried, even though the leak might have initiated a building problem with rot, insect damage, or mold contamination. This is why we argue that reliance on meters and imaging alone for water or mold detection are unreliable. But the instruments are indeed useful, in thoghtful hands. And neat too.




Reader follow-up: old urine stains leave salts, are hygroscopic, and might be picked up by a moisture meter

Thanks for your comment. One thought (using my science background) was that the moisture meter gives a high reading on what looks like an old dog urine stain (former owner had dog). I had the thought that these left over salts and ions from the urine might act as a weak conductor and activate the moisture meter.

On the internet, it seems that carpet companies use moisture meters to find hidden pet stains, because the salt from the urine can draw moisture from the air (or even just the natural evaporation of the concrete slab). So, thanks for your help. I tend to over-think things. I agree, it is a neat tool.

Examples of Scratches Indicating Animal Presence in Buildings

Noticing scratches or tears on floors, trim, even walls and furnishings can indicate a previous presence of cats, dogs, or other pets or animals in a building. For example notice the pet scratch marks on the floor trim in our photos just below.

Animal scratches on interior trim © Daniel Friedman Animal scratches on interior trim © Daniel Friedman


Continue reading at ANIMAL or URINE ODOR REMOVAL or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




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