Smells, Stains, and Musty Odors in a Basement or Crawl Space

Smells, stains, and musty odors can find their way into a basement from many sources. This section covers what causes smells and stains in a basement, including dog and cat urine stains, and what can be done to clean them up.

What Causes Crawl Space and Basement Odors?

In a word: humidity. Most Crawl spaces and basements are full of the stuff. Humidity can seep into a below-grade space continuously through the concrete and dirt walls of a basement, causing significant problems in a home as they're trapped inside the space.

If your basement walls look dry: This is not a sign that humidity is not entering into your basement. If you've ever owned a potted plant, you know that the surface can be dry even when the pot is heavy with water. This is because the moisture is pulled out by the air as soon as it rises up.

One good test to see if your basement is releasing humidity into your home is to lay plastic directly on the basement floor. Wait 48 hours and remove the plastic- if your floor is damp, then the humidity that would otherwise enter the basement was trapped underneath the plastic. Be sure to look for other signs of basement humidity as well, such as rust, mold, rotting fiberglass, and an uncomfortable feeling in the basement. Ultimately, though, if your basement smells musty, you can almost rest assured that humidity is the culprit.

Humidity will make the space uncomfortable, but humidity alone won't cause odors. The real cause of the odors in your basement is mold, rot, dust mites, and mildew in the space. Here's jsut a few things that mold can grow on:

  • Leather and Cloth
  • Drywall and Wood
  • Fiberglass Resins and Dyes
  • Paper and Cardboard
  • Paint and Wallpaper

Mold can also grow where you can't see it, such as behind drywall or wood panels. Studies have shown that this mold is just as harmful as the mold you can see. Click to read more about home mold. Or, you can click to learn more about stopping basement humidity.

In a crawlspace, the source of the problem is very similar. However, this space can also sometimes become a habitat for animals, which can live - and die - in a crawlspace. Cats, skunks, and other animals have been known to spray or urinate in a crawl space, and dead animals can create an almost unbearable smell.

Sources of Basement and Crawl Space Stains

While stains in a crawlspace are not usually something a homeowner is concerned about, basement stains can be ugly, depressing, and unacceptable to many homeowners. When they stain bare concrete, it can seem like removal is hopeless. Here are just a few ways concrete can become stained:

  • Rust from pipes, utilities, or leaky basement windows
  • Efflorescence from moisture seeping through the walls
  • Iron Ochre Stains
  • Dark Stains and Patches on Walls
  • Animal Urine Stains
  • Paint Stains
  • Oil Stains

If you have stains on your basement walls of any type, the best way to take care of the stains is to cover them with a plastic coating or a vapor barrier. Click to read more about basement wall coverings. Waterproof paints and basement wall coatings that adhere to the walls will quickly peel off and become ruined- often in as little as six months. Covering the problem with drywall and carpeting is asking for trouble as well- the moisture from the concrete basement walls can collect behind drywall and underneath carpeting, leading to mold and rot. Click to learn more about rotting basement drywall.

Cleaning Stains and Odors in a Basement or Crawl Space

Cleaning concrete stains in a basement is extremely difficult. In fact, cat urine stains in a basement floor can be so acidic and damaging that they can actually pit the concrete! There are times when new concrete is the only solution. However, there are some methods in the industry to clean stained concrete. When using cleaners, it's always a good idea to treat a small unnoticable area before treating the entire space.

Pressure Washers and Concrete Cleaning Agents: There are products on the market that are specifically made for the challening job of removing stains from basement concrete. They're designed to literally blast the offending marks off the surfaces. Pressure washers, and power washers can be rented out at local hardware stores and simlar busineses.

Bleach and Water: In some cases, simply using bleach and a power washer may work almost as well. Avialable to rent in hardware stores and other areas, they offer a great way to blast a basement surface clean. When renting such a machine is impossible, a sturdy push broom and a little elbow grease can also make a difference.

Phosporic Acid: Effective for both concrete and tile, phosporic acid is an especially good way to remove rust stains in the basement, and it works well on lime, efflorescence, grime, and hard-water deposits. Like all acids, it can lighten the color of tile, and repeated acid washes will damage sufaces. Take care not to mix this chemical with ammonia, as it will cause harmful fumes, and be sure to consult a professional before using in your home. Wear gloves when using, and apply this with a clean mop or acid-resistant brush. Resides left after cleaning and drying can be removed with a vaccuum cleaner.

Muriatic Acid: This is a solution of hydrogen chrloide in water, and one of the most dangerous chemicals you can purchase for your home. This is a highly corrosive, strong mineral acid often used for industrial applications and is used in some household cleaning projects. Hydrochloric acid should be used with great care, as it can create an acidic mist that can damage eyes, skin, respiratory organs, and intestines on contact. It can even corrode metal. Hydrochloric acid can also combine with other chemicals and cleaning agents to produce deadly chlorine gas. When using this chemical, be sure to consult a professtional and to use PVC gloves, a respirator, protective eye goggles, and chemical-resistant clothing and shoes. Be sure to dispose of leftover acid properly and immediately for your safety, and use extreme caution at all times when handling it. Never pour muriatic acid down a storm drain, sink, or toilet, as it can damage pipes and affect the biological balance of your septic system. It's not reccomended to use muriatic acid indoors, as the corrosive acid vapors can cause a great deal of damage- you should look into alternatives such as phosporic acid or TSP (trisodium phosphate) instead.

This being said, it can be a very powerful cleaning agent for masonry, concrete, and other surfaces. It can remove efflorescence and mineral deposits as well as mortar stains, and it's been known to remove pet stains and other otherwise impossible-to-remove stains. As a last resort, this may get the job done that no other chemical is. If being used to clean efflorescence, bear in mind that unless the source of this white, flaky powder is also addressed, new efflorescence will appear in time.

Coatings and Coverings: A covered smell can't reach your air. Coating over the smell with a coating such as non-toxic shellac may help keep the odors out of the space. Installing a sub floor that serves as a vapor barrier can do double-duty- keeping odors away while making your floor suitable for carpeting while also covering over the smell.

Similar coverings are also available for stained basement walls. Click to learn more!