Mold HQ
Moisture first. Mold second.

Mold starts as moisture. Learn to see it early.

A water stain, a musty closet, a window that sweats every morning. Most mold problems give warnings long before anything grows, and once materials get wet from a leak or flood, mold can start in as little as 24–48 hours. We'll walk you through it step by step, from the first thing you notice to inspecting, testing, hiring the right help, and getting it fixed for good, whether you own a home or rent an apartment.

WATER FINDS A PATH. MOLD FOLLOWS.

From first concern to a fixed home

Mold problems follow the same path every time. Start at step 1, or jump to wherever you are right now.

Step 1Notice & inspectLearn the early warning signs, then use our comprehensive inspection guide to check every common problem area in your home, one area at a time. Step 2MeasureSimple tools that back up what you're seeing with readings you can compare. Step 3TestSee something suspicious? Swab it and find out if it's mold. Step 4Get an assessmentWhen to call a professional, and why the inspector shouldn't be the one doing the repair. Step 5RemediateWhat remediation looks like, from the plan to the final clearance. Step 6Keep it from coming backEveryday habits that keep moisture in check once the problem is fixed.
Who we are

Built by people who work in mold every day

We're professionals from the mold and environmental industry, and every day we answer the same questions: How do I know if it's mold? Why does this keep happening? And how do I keep it from coming back?

Mold HQ puts the answers in your hands. Our inspection and prevention guide shows you where moisture problems usually start. The tools we recommend and products from our partners are here to educate and empower anyone who wants to know more about what's going on in their home.

And when something needs a closer look, we'll help you recognize when it's time to call a professional.

← Home

Ready to start? Most mold problems begin with something you can see or smell.

Step 1: Notice & inspect →

Notice the signs, then inspect your home

Most people start here: a smell, a stain, something that seems off. Mold feeds on organic material that's already in every home, from dust to the paper on drywall. What it needs is water. None of these signs mean you have mold, but each one means water is somewhere it shouldn't be.

  • Musty or earthy odor

    Often the first clue, especially in closets, basements, and under sinks. Your nose can find what you can't see.

  • Window condensation

    Regular sweating on glass or frames points to high indoor humidity, not just a cold morning.

  • Stains and rings

    Yellow or brown rings on ceilings and drywall mark where water has traveled, even if it's dry now.

  • Bubbling or peeling paint

    Moisture pushing through a wall lifts paint and wallpaper from behind.

  • Warped wood and baseboards

    Swelling, cupping, or soft spots in flooring and trim mean wood has absorbed water.

  • Spotting on air vents

    Dark spotting on or around heating and cooling vents, especially in bathrooms, where shower humidity rises into the vent and the duct behind it.

  • White, chalky deposits

    Efflorescence on concrete or brick shows water is wicking through foundation walls.

Noticed one of these? Here's what to do right now

  1. Write it down. Take a wide photo and a close-up, and note where it is, when you noticed it, and whether it's getting worse.
  2. Stop the water if you safely can. Wipe up standing water, turn off a leaking supply valve, or run the exhaust fan. Materials that dry within a day or two rarely grow mold.
  3. Leave it alone. Don't scrub, scrape, or open up a wall to look. Disturbing possible growth can spread it.
  4. Inspect the rest of the home. One sign usually has a source nearby, and the same conditions can affect other areas. Our inspection guide walks you through every common problem area so nothing gets missed.

Skip the bleach and paint. Covering a stain or spraying a spot can hide the evidence without fixing the water that caused it, and it usually comes back.

← Home

Your eyes and nose only tell part of the story. Readings show what you can't see.

Step 2: Measure →

Back up what you see with readings

A stain might be old and dry, or it might be wet right now. You don't need professional equipment to tell the difference. Used together, these tools help paint a picture of what's going on: where humidity runs high, which spots are wetter than they should be, and where water is showing up that shouldn't be.

Measures % RH

Hygrometer

A small sensor measures the moisture in the air. Comparing readings room to room and through the seasons shows which areas stay damp.

Affiliate link coming soon
Measures % MC

Pen-style moisture meter

Two small pins press into drywall, baseboards, cabinetry, or sills and measure how easily a tiny current flows. Wetter material reads higher. Comparing a suspect spot against a dry spot nearby shows whether water is getting in. High humidity, metal, and concrete can make readings run high, so compare spots rather than trusting a single number.

Affiliate link coming soon
Controls % RH

Dehumidifier

Pulls air over a cold coil so moisture condenses and drains away. It brings humidity down in poorly ventilated areas so mold doesn't get the conditions it needs.

Affiliate link coming soon
Finds temperature differences

Thermal camera

Shows surface temperatures as colors. Damp spots often show up cooler because evaporating water cools the surface. Confirm any cool spot with your moisture meter.

Affiliate link coming soon
Detects water

Water leak alarm

Two contacts on the bottom sound an alarm when water reaches them. Place them under sinks, behind toilets, and next to the water heater to catch leaks before they spread.

Affiliate link coming soon

Some of these will be affiliate links. When they are, we may earn a commission if you buy through them, at no extra cost to you. It never changes what we recommend.

← Step 1: Notice & inspect

Found a spot that looks like mold, or readings that point to a wet area? A swab tells you what you're looking at.

Step 3: Test →

Keep it from coming back

Whether you just finished a remediation job or caught a problem early, the goal now is the same: keep moisture from building up again. A few everyday habits, along with the tools from step 2, stop most problems before they start.

  • Bath
    Run the exhaust fan during and after showersKeep it on for 20–30 minutes after you're done. If the mirror is still fogged, the fan isn't keeping up.
  • Air
    Open windows and keep air movingCrack a window when cooking or showering, keep interior doors open, and pull furniture a few inches off exterior walls.
  • RH
    Watch your humidityHumidity naturally changes with your climate and the seasons. What matters is a room that stays noticeably more humid than the rest of the house, or humidity that stays high long after showering or cooking.
  • Damp
    Dehumidify closets and windowless roomsA dehumidifier pulls humidity down where ventilation alone can't, especially in summer.
  • Recheck
    Recheck repaired areasTake moisture meter readings on a repaired spot a few weeks after the work, then each season. Readings that creep back up mean water is getting in again.
  • 24–48h
    Dry spills and leaks fastWet materials that dry within a day or two rarely grow mold. Fix drips under sinks and around toilets right away. A water leak alarm can warn you the moment a leak starts.
← Step 5: Remediate

Walk through the home again each season. The guide includes a seasonal checklist to make it routine.

Back to the inspection guide →

See something suspicious and want to know if it's mold?

A mail-in mold test kit from our partner HomeSAFE lets you swab the spot and send it to a lab to find out what it is. Together with your hygrometer and moisture meter readings, results help round out the picture of what's happening in your home. Swab areas you can safely reach.

Mold test kit

Identifies common indoor molds, including Aspergillus, Penicillium, and Stachybotrys.

  • 2 microbial testing swabs
  • Step-by-step instructions
  • Sampling form
  • HomeSAFE bubble mailer for return
Order from HomeSAFE

Additional kits our partner offers

Asbestos test kit

Tests suspect building materials for asbestos.

  • 2 individual sample bags
  • Step-by-step sampling instructions
  • Sampling form
  • Transport bag for shipping
Order from HomeSAFE

Asbestos test kit 5 pack

Checks more suspect building materials before renovation, repair, or removal work. Also available as a 10 pack.

  • Five individual sample bags
  • Step-by-step sampling instructions
  • Large transport bag for samples and paperwork
Order from HomeSAFE

Lead dust and debris wipe kit

Measures the amount of lead collected from a sampled surface. Available with 1, 2, or 3 wipes.

  • Lead dust sampling wipe
  • Sample tube
  • Pair of disposable gloves
  • Step-by-step sampling instructions
  • Reusable shipping box
Order from HomeSAFE

N95 respirator and gloves bundle

Protective gear for at-home sampling. Not intended for asbestos removal or other high-risk work.

  • NIOSH-approved N95 respirator
  • Pair of disposable nitrile gloves
  • Also available as a 2 pack
Shop on HomeSAFE

HomeSAFE is our sampling partner, and we earn a commission on kits ordered through our links. Lab results show only what was sampled and aren't a diagnosis of your home.

  1. Order your kit
  2. Collect samples
  3. Mail to the lab
  4. Get your results
← Step 2: Measure

Results identify mold, or the moisture won't go away? Bring in a professional to find the source and size up the problem.

Step 4: Get an assessment →

When to call a professional

The guide, tools, and test kits help you spot problems and gather evidence. Bring your photos, notes, readings, and lab results to the first visit; they help the professional get to the answer faster. A qualified mold professional can find the source, determine the extent, and recommend how to fix it.

  • Your test results come back identifying mold or active growth
  • Visible growth that can't easily be wiped away or keeps coming back
  • Water damage from a flood, sewage backup, or long-running leak
  • A musty odor you can't trace, or one that keeps coming back
  • Moisture readings that stay high after you've dried the area
  • Anyone in the home with health concerns. Talk to a doctor too.
  • You need a documented professional inspection report
Who to hire

Two different jobs: assessment and remediation

Mold work is usually split between two kinds of companies. Knowing the difference helps you get an honest answer about what your home actually needs.

Step 1

Mold assessment consultant

An inspector or industrial hygienist who figures out what's going on.

  • Inspects the home and finds the moisture source
  • Takes samples and measures how far the problem has spread
  • Writes a remediation plan, often called a protocol or scope of work
  • Comes back after the work to confirm it was done right, called clearance or post-remediation testing
Step 2

Remediation contractor

The crew that fixes the problem by following the consultant's plan.

  • Sets up containment so mold doesn't spread to the rest of the home
  • Removes and cleans affected materials
  • Dries the area and fixes what's needed to stop the moisture
  • Hands off to the consultant for clearance testing

Why it's best to hire them separately

When one company both inspects your home and does the repair, it's grading its own work and deciding how much work it gets paid for. That's a conflict of interest. It doesn't mean every company that does both is dishonest, but it removes the independent check that protects you. Some states, including Texas, Florida, and New York, don't allow the same company to do both on the same job.

An example of how it can go wrong

A homeowner finds a stain under the bathroom sink and calls a company that offers free inspections. The same company that will do the repair inspects, recommends tearing out the whole bathroom and part of the hallway, and quotes a large remediation job. After the work, that same company tests its own job and says it passed. The homeowner has no way to know whether the job was bigger than needed, or whether the problem was fully fixed.

With an independent consultant, the plan is written by someone who doesn't profit from the repair. Contractors bid on the same plan, so quotes are easy to compare, and a third party confirms the work is done before the walls are closed up.

  • Ask the inspector: "Do you also do remediation?" If yes, consider getting an independent assessment.
  • Ask for the plan in writing so contractors can bid on the same scope.
  • Have clearance testing done by the consultant, not the company that did the work.
  • Check licensing in states that require mold licenses.
← Step 3: Test

Once you have the consultant's plan, here's what the actual repair looks like.

Step 5: Remediate →

What remediation looks like, start to finish

Remediation means removing mold-affected materials safely and fixing the moisture that caused them. Every job is different, but most follow the same path. Knowing it ahead of time helps you ask the right questions and know when a job is really done.

  1. The plan Consultant

    The assessment consultant writes a remediation plan, often called a protocol or scope of work. It spells out which areas are affected, what has to be removed, how the work area is contained, and what the area needs to pass at the end.

  2. Bids You

    Share the same written plan with two or three remediation contractors so their quotes cover the same work. Ask about insurance, licensing in states that require it, how long the job will take, and whether you'll need to stay somewhere else.

  3. Fix the water source Plumber, roofer, or contractor

    The leak, drainage problem, or ventilation issue that caused the moisture has to be fixed. Removing mold without fixing the water is the most common reason it comes back.

  4. Containment Remediation contractor

    The crew seals off the work area with plastic sheeting and runs air filtration so spores and dust don't spread to the rest of the home. Heating and cooling serving that area is usually shut off or sealed during the work.

  5. Removal and cleaning Remediation contractor

    Affected porous materials like drywall, insulation, and carpet are usually cut out, bagged, and removed. Materials that can be saved are cleaned, and the area is vacuumed with HEPA-filtered equipment.

  6. Drying Remediation contractor

    Dehumidifiers and air movers run until framing and other materials are back to normal moisture levels, confirmed with moisture meter readings.

  7. Clearance Consultant

    Before containment comes down, the independent consultant comes back to inspect, take readings, and often collect samples. If the area doesn't pass, the contractor cleans again and it's retested.

  8. Rebuild Contractor

    Only after clearance are walls, insulation, and flooring put back. Closing things up before clearance can seal a problem inside.

Small spots vs. bigger jobs

The EPA suggests a small area, roughly 10 square feet or less on a hard surface like tile or a window frame, can often be cleaned by the occupant. Anything larger, growth that keeps coming back, anything inside walls or the HVAC system, damage from sewage or flooding, or anyone in the home with health concerns calls for a professional.

If you rent

  • Tell your landlord or property manager in writing, with photos, dates, and any readings or test results.
  • Keep copies of everything you send and receive.
  • Repairs are usually the owner's responsibility. Check your local tenant rules for how quickly they must be made.

Insurance

  • Call your insurer early and keep photos, readings, lab results, and receipts.
  • Many policies cover sudden water damage, like a burst pipe, but limit coverage for mold from long-running leaks. Check your policy.
  • The consultant's report and plan help document the claim.

While the work is underway

  • Stay out of the contained area, and keep kids and pets away.
  • Ask for updates as each stage finishes.
  • Ask for a copy of the clearance results before the rebuild starts.
← Step 4: Assess

The area passed clearance. Now keep moisture from building up again.

Step 6: Keep it from coming back →