Mold on the wall: when you can clean it yourself and when you should not

The quick answer on doing it yourself

You can usually clean a small patch of mold yourself if it is on a hard or nonporous surface, the moisture that caused it is fixed, and the area is less than about 10 square feet, which is the size the U.S. Environmental Protection Agency uses as its do-it-yourself guide. Call a professional if the growth is larger, if it came from sewage or other contaminated water, if it is inside the heating and cooling system, or if anyone in the house has health concerns. In Texas, mold remediation covering 25 contiguous square feet or more generally falls under state licensing rules.

We are SERVPRO of Park Cities. Juan and I own the company, and mold calls are part of our work in Dallas, Highland Park and University Park, almost always as the tail end of a water problem. This guide is meant to help you decide honestly which side of the line you are on, and to do the small job safely if it is yours.

Mold is a water problem first

Mold spores are present nearly everywhere, indoors and out. What turns them into visible growth is moisture that stays put: a slow leak, a sweating pipe, a wet carpet pad, a bathroom with no ventilation. The EPA is direct about this. The key to mold control is moisture control, and if you clean the mold without fixing the water, it will come back.

Humidity counts as moisture too. A bathroom without a working exhaust fan, a closet on an exterior wall that never gets air movement, or a room that stays damp after a carpet cleaning can all grow mold without any leak at all. In those cases the lasting fix is ventilation and drying as much as cleaning, and the growth will keep returning until that changes.

So before you think about cleaning, find the source. Look above and behind the growth for plumbing, a window, a roof penetration, an HVAC line or a spot where outside water gets in. If you cannot find it, that alone is a reason to bring someone in, because hidden moisture usually means the visible patch is only part of the growth. My guide to the signs of hidden water damage covers where to look.

Two size lines that matter: 10 and 25 square feet

Homeowners sometimes hear two different numbers, and both are real. They answer different questions.

The 10 square foot figure comes from the EPA's homeowner guide. It is practical safety advice: if the moldy area is less than about 10 square feet, roughly a three-foot by three-foot patch, you can generally handle the job yourself following its guidelines. Above that, or where there has been a lot of water damage, the EPA suggests getting professional guidance.

The 25 square foot figure comes from Texas law. The Texas Department of Licensing and Regulation says areas of visible mold of less than 25 contiguous square feet can be cleaned up by people who are not licensed. Larger projects bring in state licensing, and under TDLR's rules the same company is generally not allowed to do both the mold assessment and the remediation on the same project. In practice that means a licensed assessor writes a plan, called a protocol, and a separate licensed remediator carries it out. The rules have exceptions and details, so confirm anything specific to your property with TDLR.

Situations that are not a DIY job at any size

Size is not the only test. Some conditions make even a small area a job for trained people with containment and protective equipment.

• The water that caused the growth was sewage or otherwise contaminated. The EPA recommends calling a professional experienced with that kind of damage.
• You suspect mold inside the HVAC system or ductwork. The EPA advises not running the system if you know or suspect it is contaminated, because it can spread spores through the house.
• Growth is inside a wall cavity, under flooring or above a ceiling, where you cannot see its full extent.
• Porous materials such as drywall, insulation or carpet are affected over a large area, since those usually need removal rather than cleaning.
• Someone in the home has asthma, allergies, a weakened immune system or other health concerns. Talk to their doctor before anyone disturbs the growth.
• The mold came back after you already cleaned it once, which means the moisture source is still active.

How to clean a small patch safely

If your situation passes the tests above, the job is manageable. Wear gloves, goggles without vents and, as the EPA suggests, an N-95 respirator that fits properly. Keep children and pets out of the room. Open a window if you can, but do not run fans that blow air across the growth toward the rest of the house.

On hard surfaces such as tile, glass, metal and sealed countertops, scrub the mold off with detergent and water and dry the surface completely. The EPA notes that bleach is not recommended as a routine part of mold cleanup, and never mix bleach with ammonia or other cleaners, since the combination produces toxic fumes. Porous materials that are moldy, such as ceiling tiles, carpet or a section of drywall, may need to be removed and replaced rather than cleaned.

Bag the cleaning materials and anything you remove before carrying them through the house. Then watch the spot for the next few weeks. If growth returns, the moisture problem is not solved.

• Fix the leak or moisture source first
• Gloves, goggles and a properly fitted N-95
• Detergent and water on hard surfaces, then dry thoroughly
• Remove and replace moldy porous materials
• Bag waste before moving it through the house
• Recheck the area over the following weeks

Testing: when it helps and when it is a waste

Many people want a test before they do anything. If you can see the mold, the EPA says sampling is usually unnecessary, and there are no federal limits for mold spores that a test result could be compared against. What you need to know is where the moisture is and how far the growth goes.

Be cautious with anyone who offers a free mold test and then quotes a large remediation based on their own results. On a licensed Texas project the assessment and the remediation are generally handled by two different companies, and on a small job you can usually see what needs to be done without a lab report.

Testing has a clearer role in two situations: when you smell mold but cannot find it, and after a remediation, to confirm the area was cleaned properly. On a Texas project above the licensing threshold, the assessor's protocol and post-remediation assessment are part of the process. An independent environmental inspector like Zeke D'Avy can assess the property and write that protocol before any remediation starts.

What professional remediation involves

Professional mold work has three parts that a homeowner usually cannot replicate: inspection to find the extent and the moisture source, containment to keep spores from spreading into clean areas while work happens, and removal of contaminated materials with cleaning of what remains. That is the scope we describe for our own mold service, and it is usually paired with drying, because whatever grew the mold is often still wet.

On a licensed Texas project, the work follows the assessor's written protocol, and TDLR requires licensed assessors and remediators to give the property owner a Consumer Mold Information Sheet before mold-related work begins. When the project passes clearance, a licensed remediator can issue a Certificate of Mold Damage Remediation, which TDLR notes may be presented to an insurer. Whoever you hire, ask for their TDLR license number and check it on TDLR's license search before work starts.

Once the area is clean and dry, our reconstruction team replaces the drywall, insulation, trim or flooring that had to come out, so you are not left with an open wall.

Insurance and mold, briefly

Coverage for mold depends heavily on what caused it. The Texas Department of Insurance explains that if mold develops on an item damaged by a covered water event, it would generally be covered, but most home policies do not cover damage from gradual leaks, and many do not include mold cleanup and testing after a damaged item is removed. You may be able to add mold coverage to your policy.

That is one more reason to deal with water quickly. A burst pipe dried right away rarely becomes a mold job. For more on how claims work, read how Texas homeowners policies treat water damage and mold, and talk to your agent about your specific policy.

If you decide to call us

Tell us what you see, roughly how large it is, what you think caused it and whether the water is still active. If the problem is mostly water, we can start by finding and drying it. If it is clearly a mold project of a size that needs Texas licensing, we will talk through how the assessment and remediation steps fit together for your property, and who does each one.

If you manage a building, the same logic applies at a larger scale: find the moisture, contain the affected area, keep occupants informed and document every step. We work with property and facility managers who would rather have a plan in place before the next leak than make one during it.

Either way, you should come away knowing where the moisture came from, what is being removed and why, and how the room will be rebuilt. If you are comparing companies for this work, the questions in what to ask a restoration company before it starts apply to mold just as much as to water.

Questions people ask me