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What's the best way to get rid of mold in a basement and prevent it from returning?

Updated December 11, 2020
The Angie’s List Answers forum ran from 2010 to 2020 and provided a trusted space for homeowners to ask home improvement questions and receive answers directly from Pros and other users. This is an archived question from the Answers forum.

Question by bigblett: Have traces of mold across parts of my basement walls. How is the best way to kill and remove it, and then to prevent it from coming back?

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Answered by vermontguy: Mold in a basement is a common problem. My company helps people with this every day. Some of the answers you received were helpful but not all the information is correct. First, you need to eliminate the two main ingrediants that mold needs to survive. The first one is water intrusion. This is a must. I am assuming you have no water intrusion as you make no mention. The second componant that needs to be eliminated is moisture. Moisture is also humidity. Basements need to be kept airtight in the summer months. Some folks have posted that you need air flow in your basement. Nothing could be furthur from the truth. When you open any windows for example, not one micron of air goes out of the basement, Warm humid air is sucked into the basement. Houses suck air into the basement and it meets the cool surfaces and skyrockets humidity. The windows must be kept closed and a dehumidification device installed to ensure humidity stays below 60% humidity. The dehumidifier should be energy star rated and purchasing a seperate humidity guage is a must to monitor the unit's progress. We like to keep our customer's basements at 50% humidity. This eliminates the smell that is active mold spore growth. Once the water and humidity is brought under control. Remove the organic materials that have mold on them. Walls, sheetrock and studs that have been affected. Follow the advice of previous posts as you must ensure that you do not affect the rest of the home. Once removed, install new walls using as much inorganic material as possible. We also install vapor barrier over the walls and seal the floors to stopwater vapor transmission into the basement. Poly plastic is not a acceptable vapor barrier. It is not "zero-perm" and will still allow moisture transmission. It will also crack and break into pieces over the years. A PVC liner rated "zero-perm" is the correct product in this application. Depending how large the basement is and if it is sectioned off will determine the dehumidifier strength. We use the Santa Fe line of dehidifiers as they are super energy efficiant and work like a dehumidifier on steriods. I hope this helps and I wish you the best in Basement Health!


Answered by Cas: What type of walls do you have in your basement? Sheetrock and studs most likely need to be removed if they're moldy, but block walls can be cleaned with a hard (dry) brush, bleached and quickly dried. There are also many mold cleaners available at your local hardware store--including some green options. (Be sure to wear a mask and ventillate the area if you're going to attempt a DIY. Hiring a mold removal specialist is also an option.)

To keep the mold from returning, you'll need to find out where the moisture and dampness is coming from. Have a dehumidifier on hand and be sure to properly vent the area and increase air flow if possible.

Answered by LessTalkMoreHawk: I believe you can also get paint that will prevent the spread of mold.

Answered by bmock: As previous answer stated...find the moisture problem and you will solve your mold problem. Find a contractor that has experience dealing with below grade moisture issues and have them try to determine the cause of the moisture and what some remedes might be. This can be a very complicated issue or one that is as simple as deverting the water away from your house with gutters. Best of luck with finding the resolution!!

Answered by Able Realty: You may need to remove drywall and insulation - studs only if they are rotten. You will obviously want to stop future leaks so repair the foundation if it's cracked, get a battery backup on your sump pump, or repair the leak by the roof or window that's leaking. Once the cause has been fixed, you need to stop the mold. Bleach diluted with water and sprayed can take care of most minor mold problems. But if you want to be ultra safe or if you have a lot of mold or potentially dangerous mold, you will want to have a professional company fix it. There are mold remediation companies that charge a lot of money for this. However, I think the most effective treatment is with Ozone, as it will kill all mold and mold spores. You will need a company to do this as well. You also will have to leave your home (with all pets) for at least 24 hours, as the ozone is toxic to breathe.

Answered by zeus1620: 1. Correct Moisture Problem2. Install dehumidifier to reduce RH (relative humidity) to a level below 55%3. Set up / operate negative air machine (hire contractor or rent a unit short term)4. Seal any floor vents or duct work leading into living space5. REMOVE ALL SHEETROCK AND INSULATION (if you have any)6. Sand infected areas lightly7. Spray apply biocide (or lysol concentrate) to all lumber surfaces (upper floor joists and subfloor)8. Allow 48 hours dry time (RH should once again come down under 55%)9. Spray apply a good mold inhibitor (olympic makes a good product for this)10. install new R 19 insulation (if there was any)11. call a local inspector or remediation company for an air test to insure you have dealt with the problem correctly.BY ALL MEANS DO NOT USE CLOROX OR BLEACH, IT WILL ENHANCE YOUR PROBLEM DRAMATICLYGood Luck


Answered by gary clemons: You have to get rid of the moisture proublem, buy fixing the water from coming into the basement, or fixing the moisture problem, or leak that has accured in the basement, this is never a quick fix unless you have a leaking drain line, leaking water pipe, hvac drain stoped up or bad pan and in some cases it could even be coming from a roof leak that has not shown up in the home.


Answered by Serge Construction: The bast way to get rid of mold it just use blich 1 : 10 ratio (1 blich + water) all pros use it . Save money and use it . sometime I use 50% +50% Do NOT forget Gloves. $5.00 on materials and spray bottle solve your problems.Serge Construction & cabinetry.

Answered by lucky nana: thank you

Answered by paulrobbins: First of all any water penetration must be stopped and averted. Mold will not grow in relative humidity below 45-50%. If there is mold and it is removed it will begin to grow back in moist conditions. Severe problems need to be treated professionaly but in any case moisture needs to be controlled. Dehumidifiers are not the proper solution. They take water molecules out of the air but do not remove the mold spores. They are airborne and air naturally rises by way of stack pressure. Once it rises it infects the living space above. The healthiest answer for improved indoor air quality is to install an approved venilation system. Properly installed, the conditioned air from above will be drawn across the basement or crawl space floor and be expelled from the house. The system we are certified to distribute and install is called EZ Breathe. It can remove the air from the average home approximately 6-10 times a day, providing a much healthier breathing environment. paulrobbinswoodworkingco.

Answered by APAPaint: Most of the suggestions are good ones, however I think they all miss a very important point. Concrete can thru the cource of a year move GALLONS of water in and out of the home. If your foundation is exposed, than after or before using some of the following suggestions regarding removing modly material and such, the foundations needs to be sealed on the inside AND the out side preventing water from coming in and out in the first place. If you cant reach the outside of the foundation install a vapor lock on the inside of the foundation wall and install gypsum dry wall. Use a good quality primer to seal the drywall and paint. For added bonus and not much more money you can add mold inhibitors to paint sold at most paint stores.


Answered by LCD: Most of the comments are right on about having to get rid of the source of the moisture first, otherwise you will have a permanent battle on your hands. If it is general light mold around the basement and there is no staining from outside water instrusion, then you probably have a general humidity problem. You could check on that by tearing a hole about a foot around in the worst looking spot if it is drywall or panelled - if there is mold smell or black or fuzzy white mold/fungus on the back of the piece you take out, on the studs (or rust or free moisture if metal studs), or mold or dampness on the foundation wall then it is more than just interior humidity - you probably are getting moisture through the wall from outside. This is the most likely case, unless your basement has no circulation with the rest of the house.

Another clue would be if any metal items (pipes, joist nails, etc) in the basement are rusting. Also, if the mold is appearing on spots other surfaces in contact with the outside ground (like interior walls, furnishings, stair risers, ceiling or underside of main floor) then your general humidity is definitely WAY too high, and probably means you either have no ventilation in the basement, or you have leaks through the foundations or around the basement slab.

You locally get a feel for diffusion through wall or slab by temporarily tightly taping a piece of plastic sheeting over a section of the wall or floor - leave it overnight, and if it has noticeable condensation on it the next day you have excessive moisture diffusing into the room from that surface.

You can get a decent humidity gage at a hardware or box store for about $7-10 - if your humidity is over about 70% then you are too damp. What reads as about 70% in the basement room can mean 100% (condensing conditions) at the colder exterior walls.

Stopping actual flowing outside infiltration requires going outside, removing the fill from around the house, and installing a membrane or bitumastic waterproofing system (and possibly drains) around the entire foundation - $10K + typically.

If you think it may just be interior moisture condensing on the colder surfaces, then removing the moisture is the key. If you have exposed concrete or concrete block walls, there are moisture-retardant paints that will limit vapor movement through the foundation. It will NOT stop actual leaks - just moisture diffusing through the foundation from the moist ground outside. There are separate trafficable moisture-control paints for bare concrete floors. A bare floor and wall full-house basement that is wet onthe outside surface can contribute up to 5 gallons of moisture a day to the house - more than enough to cause condensation in the cooler basement. These measures you can do yourself according to the instructions on the cans (after the bleach and scrubbing treatment to kill and remove the existing mold - read up on mold removal techniques and safety on Federal Housing Administration or Cooperative Extension Service websites). You can also buy mold and mildew inhibitor packets to add to the paint at your paint dealer.

Also check if you have any exposed dirt in a connecting crawl space - some houses have a half basement with only a crawl space under the garage and/or family room, and if there is not a tight and effective vapor control barrier over the bare ground then a lot of moisture can get into the basement air from there.

An open sump pump sump with standing water can also contribute a fair amount of moisture - you may beable to cut a piece of plastic to fit over the sump (leaving clearance for the mechanism to operate) to reduce this source - fasten down so it cannot be kicked and block the operation of the float switch mechanism.

Substantial ventilation and/or dehumidification can also remove a fair amount of moisture, but that is an on-going battle. Ventilation should be with low moisture air (inside air - heated if possible, as warm air will collect more moisture when it mixes with the downstairs air) if possible, especially if you live in an area with high summer humidity outside, and the airflow has to be enough, and distributed around the perimeter of the room (large stand-up fan ?), to actually collect the moisture, and then of course it has to be vented to the outside to get rid of the now-moist air.

One solution used in some houses is to duct heater and air conditioner air into the basement as well (which is usually not done in unfinished basements), or to install a "Robin Hood" fan between the main floor and basement, to steal some air from the main house and blow it around in the basement. This is not the best solution, because the return air is vented into the house, so the moisture is not being removed from the house envelope.

All this can be addressed by an energy efficiency consultant, or by an HVAC (HEating, Ventilating, and Air Conditioning) contractor if you don't want to attack it yourself.

Answered by koja: Basements are naturally wet. First remove moisture, dehumdify your basment by running a basment dehumidifier which dries the air. Make sure to repair any sources of water or condensation including wrapping pipes that sweat, fixing cracks in foundations, making sure that dryer is vented outside... Clean the walls with Vital Oxide which kills mold on contact and will repel mold growth for some times as long as water source is cut off. Then after walls dry ( assuming they are concrete) use a HEPA filtration vacuum to suck up the dead mold spores. Dead mold spores can also evoke a response. Use a hygrometer to measure humidity in the basement. Make sure it is always below 55%. Run a basement dehumidifier to dry the air as mentioned before.(really important).


Answered by bobculley: Dear Readers,

The best and only way to prevent mold amplification in a basement is to prevent moisture or water from infiltrating the materials prevalent in most basements. The sources are flood, broken water supply lines, leaks from drainage pipes and humidity. With the exception of humidity, all water infiltration possibilities should be dealt with quickly. Remove the water you see and place a dehumidifier, and air movers to increase ventilation while the dehumidifier does its job. If you have a moisture meter, monitor the materials each day to make sure the materials are drying. If the materials are dried in 72 hours or less, you shouldn't have an issue with mold.

Humidity that exceeds 55-60% is enough moisture for mold amplification to start and sustain itself under the right set of circumstances. If humidity is your problem, you should consider a small commercial dehumidifier made for these scenarios. Increasing ventilation is also a real good idea. You should also make sure the air circulates in your basement at least 4 times an hour, if not, contact your Angie's List HVAC contractor and have them look into increasing the air circulation.

Finally, repair the source of your water infiltration, and keep the basement dry. This will take care of any mold issue that you may have. Good luck!

Bob Culley


Answered by Guest_9265593: if you have carpet down there id tear it up if it got wet and stayed wet for more than 72 hrs its all a home to black mold deadly black mold. we had this problem so its my experience. i bought a big thing of bleach. we tore up carpet n pad shoveled up the trim pieces to hold the carpet along floor boards. i took a scrub bruch n scrupped it all with bleach. this was in our basement room(mancave actually) so we spent time down there. it always had a creek flowing thru it so we got floor padding and layed two layers with tape along the seems cauked up all the floor gap n layed inter locking floor boards(fake wood floor) and clear cauked all around twice. since then about 6 months with the wet season(winter when this happened) no water none not a drop in that room the bleach killed it all we re painted since it was painted walls all gone no more mold and we burned the carpet nothin no mold no water all fresh now looks amazing and as a mommy i feel safe with my kid playin down there now

bleach n a scrub brush

Source: own experience

Answered by Guest_98939372: if they are solid use bleach, also if you have discovered that the mold has spread to carpeting and furniture you can use vinegar or lemon juice and salt to remove it

Answered by Guest_9388144: Mold spores are on everything, unless you are in some type of vaccum clean room. All they need to flourish is oxygen, a constant source of moisture, and temperatures above freezing.

The first thing I would do is try to remove the source of moisture by sealing any penetrations, and removing any material built up around the exterior of the home. I would then apply a plant based non toxic mildicide. I generally use Sporicidin Disinfectant which I purchase from I would reccomend putting it into a pump sprayer and generously apply it to your walls, floors, etc. It not only kills all mold spores, etc, but it takes away odor and has a proven residual effect up to 6 months.

The next step and most important is to purchase a home use dehumidifier, my unit is programable and is set to turn on if the humidity in the air reaches a certain level. I have purchased them brand new as well as found good qaulity used ones on Craigslist for 100 bucks or less. Leave the unit on for 3 or 4 days to get the basement nice and dry ( It also depends on the size of the basement.), it will also suck the moisture out of the walls, then program it to turn on when the humidity reaches about 55%. If you keep the dehumidifier constantly monitoring the baement you should never have another moisture / mildew issue. Unless of course your basement floods.

Source: I am a construction estimator / as well as water damage certified through IICRC

Answered by waycoolmom1: 1. Determine source of moisture and correct. (some ideas: NDS EZ-Drain French drain, about $50 for 10 ft section at Lowe's, Home Depot and does not require use of gravel; Henry 787 Elastomeric Fluid-Applied Waterproofing Membrane applied to outside wall, etc. - Google for details and reviews online, around $125 for 5-gallon bucket.)

2. Treat entire basement and contents with Concrobium Mold Control (5-gal bucket available through Home Depot online, etc., approx $130) using a Concrobium Mold Control Fogger (just over $300). This product works and is not toxic. It does not contain Clorox. Easy to do it yourself and save $$$.

3. Purchase a quality dehumidifier to remove the existing moisture from the area. (PerfectAire 50pt, PA50, from for just over $200 works great. Can be used with included reservoir or connected to your provided hose for continuous draining.)

Source: Personal experience

Answered by Guest_94244121: Once you thoroughly dry the basement and rafters and all cinderblock and wood with fans for approx. one week, you apply Mold Control, purchased by the gallon at Home Depot or Lowes. We used 30 gallons for 1,400 sq. ft. Wait 2 weeks and examine total area for mold, if none, hire an insulation company to spray closed cell polyurethane foam which is mold-proof, water-proof, fire-proof, sound-proof, and will add strength to the structure. Guaranteed for life. Well worth it.

Answered by Guest_9405397: We had MasterDry install the moisture barrier and a dehumidifer in our crawlspace. This stopped the mold and humidity in the crawlspace and no more moldy smells wafting upstairs into the living space. I keep a humistat and check it periodically to keep it below 50%...

Answered by Guest_96818754: ...from Colorado, I'll offer these suggestions:

First.....take mold seriously! your homeowners insurance company and see if you're covered for water damage. If so, they will call in a Professional Team. They know what they're doing.

Third....if you insist on doing it yourself, it would be best if you used the appropriate filter mask, wear the appropriate gloves, maybe even wear protective clothing. (I can't be more specific because you'll all be from different climates...the mold might be different...some are very dangerous, some not so much)

Fourth....I'm going through the whole routine for the second time. Although I will be paying for the cause of the is covering the rest. (and my insurance isn't "luxury insurance")

Fifth...verify your information, it can't hurt...Google loves to help. I suggest that you look for sources of info from Universities, State Agencies, get my drift.

Good Luck to matter how you tackle those tiny critters...

Source: Baawb

Answered by Guest_98052007: Regarding prevention of mold:

We recently had a Radon mitigation system put in the basement. This evacuates air from under the basement slab and sends it outside via a fan inside a pipe. It has the added benefit of completely removing moisture from under the slab, which should prevent mold from forming if the cause is moisture coming out of the ground. Our basement is now very dry!

The cost is this area (Maryland) is typically under $1000.

If you have moisture coming through the walls, the best way to mitigate this is to add topsoil around your home and grade it so rainwater/snowmelt runs away from the house. Make sure downspouts from the water direct water away from the house too. This is VERY important, and surprisingly, many people try to solve the problem from the inside without considering why the water is intruding in the first place!

Answered by Guest_9416376: This works on both block or drywall. First, spray the whole wall with Clorox Cleanup and wipe with a cloth. Do it twice if any mold is still visible. Let everything dry. Then paint the wall with two coats of a good primer sealer such as Kilz. This will seal the area so no mold spores can escape or grow.

This has worked very well for me; no odor, no new mold and a primed wall ready to paint.

Oh, and do keep your basement dry from here on.

Answered by Guest_9308181: I know this is an old question and you have received many good answers, but I couldn't let it go by without adding one important FACT in case anyone else uses it as a reference: BLEACH DOES NOT KILL MOLD! Anyone who is using mold to kill bleach is doing themselves a disservice and introducing an awful toxin into their living space, which will add to their already toxic air quality. Short of typing out a million-lines-long response, I suggest that anyone who has encountered mold in their home search this topic on the internet and get a product that specifically kills mold. Bleach is just going to give you very clean mold...

Answered by Guest_9803300: Bleach does NOT kill mold - it only bleaches it so's it is not visible.


Spray your walls down with vinegar to stop mold from growing.

I had a problem in the basement and once I figured out the bleach was doing nothing took the advice from a chemist friend and sprayed the areas with white vinegar. I haven't had a problem since. I use a dehumidifier in the summer if I don't have the A/C turned on.

Good luck

Answered by Jennyb: I'll try to directly answer the first part of the question: "How is the best way to kill and remove it" (it being the traces of mold across parts of basement walls).

All non water proof-sealed basement (and household) walls are porous. For all porous surfaces use a spray of 80% vinegar (8 parts vinegar to 2 parts water) to saturate the surface, then scrub the surface with a microfiber cloth rinsed and rung regularly in 40% vinegar.

The deeper the vinegar penetrates the surface the better the chance that it will reach the roots of the mold (or as the Aussies spell it: mould). Vinegar is non toxic so there is no fear, from a health perspective, of using too much. Scrubbing the surface has multiple purposes which can be explained upon request.

It is important to read mold removal product labels (including bleach) carefully: All say they are for non-porous surfaces only. The reason is because of the chemical nature of bleach preventing it from being absorbed to, and by, the roots of the mold so the mold might lighten in color, but the roots are still alive so the mold is never killed.

Rubbing alcohol is also listed to be able to penetrate and kill mold. However, because rubbing alcohol is highly flammable, it not recommended often. Always use the less flammable 70% which is proven to be just as effective and it should never be used near open flames or in an unventilated area or over large areas (spot spraying trace mold on a wall in a ventilated basement away from the water heater and furnace might be safe). When we had a roof leak the ceiling got wet and molded in an unused room upstairs before we even new we had a leak. The ceiling being a painted surface is porous so I sprayed it with alcohol waited 15 minutes then blotted up all of the moisture and black yuck with dry towels. No traces of mold were visible after treatment. No mold returned. However it did remove some of the white paint on the ceiling and we did decide to repaint the ceiling a few months later. LOL- and we did get the roof fixed - moisture problem eliminated.


Answered by Guest_90654731: There are lot's of great info in this forum. Studs can be sanded till free of mold, then treated with Concrobium. I've used it to clean my basement, even in laundry.

Also look into Zyprex to make concrete waterproof. Very interesting stuff!

Answered by graceed1963: I have a similar problem in a finished basement room. The walls and floor are getting moldy and the washing machine is starting to rust. I rent and hate to ask my landlord to fix things- hes a great landlord and fixes all problems right away but its so costly.

Answered by Guest_9716393: .

Answered by LCD: One thing about VermontGuy's good comments - he is adamant against ventilation, especially in summer. That is a bit hardline - imagine a wet basement (say a river bottom area with wet soil) in the Mohave Desert with 10% outdoor humidity - certainly ventilation will remove moisture, and in fact in many areas without very hjigh summer humidity just adding ventilation will remove a lot of moisture - that is how crawlspaces work. Of course, bringing in outside air fights with your A/C if it is on.

Also, he started open windows will exhaust no moisture - that is not always true, especially in tight houses with outside fresh air makeup at the air handler. Also, even if the air from the windows goes upstairs as is usual, it will remove a significant amount of moisture - though of course you have to be sure that is not raising the upstairs living air humidity to unacceptable levels.

When talking ventilation, you need to distinguish between interior air recirculation (especially with an A/C operating, which acts as a dehumidifier at most times) and outside air also. Even if the outside air is humid and warm, so may actually condense as visible moisture when it get into the basement, increasing recirculation of interior air - sometimes using the return air from the A/C system (so warmer and does not increase the relative humidity as much) can work well, depending of course on where your air handler picks up the return air. I have seen a lot of buildings where the return air is run through the basement to pick up moisture there, then back into the A/C system for dehumidification (either at the evaporator or separate dehumidifier). Of course, it has to be connected correctly - you do not want to be running moist air across the furnace, for instance.

Of course, in serious cases, direct dehumidification in the basement is the best solution - and without the very common error or dumping the collected water into an open sump pump pit or even running across the concrete floor to a sump, which puts a lot of the moisture right back into the air ! And no swamp coolers in the basement or any other area with high humidity issues - which in humid areas might rule out the entire inside of the house in the summer.

Answered by Guest_9232368: Scrub the walls with a solution of hot water, bleach and vinegar. Also pour some hydrogen peroxide on the scrubbing rag or mop. Let the area dry. Then spray with concrobium spray. (Get it on Amazon or Walmart online) If you can afford a dehumidifier, that will help too. Concrobium helps keep the mold from coming back.

Answered by Guest_9271599: your cheapest and probly most effective if you dont feel like spending tons of money on framing it out and what not. frist i would spray the walls and scrub them with mildicide. wall dehumidifire is running. wait to dry then paint the cement walls with DRYLOCK.

Answered by Nikodem: The best and probably cheapest solution to get rid of mold, mildew and moisture.Non-invasive method, no chemicals and so

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