# Black mold on plywood subfloor



## Moody

Hello everyone,
I just bought a house in Las Vegas, Nv. I got a great deal on a foreclosure and it needed some work as expected.

I am planning on installing some ceramic tile. Well today I pulled out the berber carpet, padding, and baseboards from the upstairs bathroom and this is what I found...
























Now it looks as though the lower portion of the drywall behind the toilet needs to be replaced. Im unsure if its acceptable to proceed with laying cement board over the plywood subfloor. I have treated the area with a bleach solution. 

Any advice would be greatly appreciated 

Thanks


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## DangerMouse

hi and welcome to the forum.
was it wet still? is it soft and rotting? bad there.
some mold in a damp area is to be expected when tearing apart older stuff. moisture WILL work it's way in....
is the bleach working? 
if it's still solid, clean up the mold and proceed.

DM


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## Moody

The dry wall is rotted but the plywood seems good. The was some moisture behind the toilet due to a leaky valve. It is all dry now. I was unsure if it was common to find this condition and if laying over it it advisable.

Thanks


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## Moody

There is some lippage in the plywood seam due to the wood swelling from moisture. If laying over is advised I assume these should be sanded down correct?


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## Maintenance 6

I would seal it with some Kilz or Zinnser, before you cover it. As long as the material is solid and still structurally sound, it will be OK. If you are going to sand on it, wear a respirator and run a HEPA vac. You don't want to be blowing dead mold carcasses into the air more than you have to. They can be an allergen for some people.


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## Moody

Thanks for the input every one.

So I cut out the area(s) of drywall that had mold. Here is a pic of the area behind the toilet.
















and the area by the tub 

















I then treated the plywood with a mold cleaner I bought from Home depot. 









When at Home depot buying supplies for this project I showed a guy in the paint department the pics from my original post and he said that I needed to pull the plywood subfloor and check underneath to see if the mold had spread and if it had that any affected areas would have to be removed. He was very adament about pulling the subfloor. I thought this to be a bit extreme but thought I would mention it just to get your opinions. I can only post 6 pics in a reply so I will continue where I left off in the next post.


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## Moody

Here is what it looked like after treating the plywood with mold cleaner.

Behind the toilet

















and by the tub
















The cleaner did a pretty good job of removing the mold. There is still some black in the crevices where the wall and tub meets the floor. I am concerned about the swelling in the floor.
















should I sink some stainless steel screws near the swollen seam first and the then sand it down flush? 

Also, there are alot of holes in the plywood from where the carpet tack strip was nailed down. Should these be filled with some thing? There are rusted nails as well. Should I pull the rusted nails and replace with some SSteel screws? 

My plan is to get the subfloor as clean and smooth as possible and then apply some Kills mildew resistant primer. Then mortar and screw down Wonderboard and then lay ceamic tile. 

This bathroom does not have a window that opens but does have an exhaust fan. My two kids will be using this bathroom so it will be used frequently. I think I will wire the fan to always turn on when the light is switched on. I am also going to apply a new coat of paint with a anti-microbal additive. I will be relpacing the rod and curtain with a sliding door to help keep the water in the tub/shower enclosure where it belongs. I am also contemplating putting in a dehumidifier as well. Any advice on keeping this mold from returning is greatly appreciated. 

Do you think I need to pull the subfloor and inspect underneath? I'm pretty sure that the moisture from the area by the tub was from people dripping as they exited the shower and the shower curtain being compromised. 

Thanks again to everyone

Moody


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## DangerMouse

i don't think so, it's pretty obvious the mold and mildew was from having berber carpet and pad in a bathroom....
one minor problem you may have is resetting a toilet. be sure the flange and flooring are the right height.

DM


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## Maintenance 6

I surely wouldn't go to the hassle and expense of pulling the floor up if it's still solid. Sand the high spots a little if you have to. I wouldn't even pull the rusty nails. Install some galvanized ones next to them or the stainless you talked about. You are going to cover this whole thing and seal anything in there away from your living space. If there was any mold in there, it will go dormant when the moisture is removed. The whole thing does not appear to have an extreme mold problem. More or less typical.


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## Bahar

Moody said:


> Hello everyone,
> I just bought a house in Las Vegas, Nv. I got a great deal on a foreclosure and it needed some work as expected.
> 
> I am planning on installing some ceramic tile. Well today I pulled out the berber carpet, padding, and baseboards from the upstairs bathroom and this is what I found...
> View attachment 11222
> 
> 
> View attachment 11224
> 
> 
> View attachment 11225
> 
> 
> Now it looks as though the lower portion of the drywall behind the toilet needs to be replaced. Im unsure if its acceptable to proceed with laying cement board over the plywood subfloor. I have treated the area with a bleach solution.
> 
> Any advice would be greatly appreciated
> 
> Thanks
> 
> 
> 
> 
> View attachment 11222


It is always better to have a professional come in and take care of the mold if you do not know what to do, I was told that bleach is not a cure all for black mold however there is a solution you can use I just don't remember the name I know about it because I watch Income Property with Scott McGillavray and he had mentioned it numerous times I also watch Holmes on Homes and in a situation like this Mike just replaced all the flooring wood and all etc... Be careful and stay safe with this situation!!!


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## rusty baker

Just be careful. All those home repair shows, give some wrong advice. Even Holmes.


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## CyFree

According to both the U.S. Center for Disease Control and the Environmental Protection Agency, there is no 100% effective or safe way to completely kill or cleanup mold from an organic, porous and absorbent surface, such as drywall, plywood, and fiberglass insulation.

Once the mold settles in these, it spreads deep in the material and chemicals will usually not penetrate the core deep enough to kill it.

They clearly state that these materials should be completely and carefully removed and discarded, rather than threated with any kind of chemicals.

I'd strongly suggest you consider that before you spend all that money to remodel the whole bathroom, only to see mold coming back a few weeks down the road.


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## nolamar

I know this is an older thread, but what caught me is you said there's swollen subfloor. That's from moisture damage and should be replaced. Looks like you did a good job of cleanup, but mold doesn't clean up well. Here's what I found after tile and tub removal:









The subfloor was soft, swollen and splitting apart under the tub, so removed. See here:









So, we replaced the subfloor under the tub area as well as replace the wallboard that was moldy. No good to just clean it.


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## AliceT

looking much better.. nice job!


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## <*(((><

Kilz does not help that situation (at least that is what a mold specialist said) unless they have come out with a EPA registered mold paint, there are special paints that are EPA registered for mold. I've talked with a mold remediator contractor and he recommended that you have a HEPA mask and a HEPA filter in a shop vac, and sand down the moldy areas and vacuum the dust. He said to make special sure that you don't touch your eye or around your eye when handling the mold situation as it can cause blindness if the mold gets started on your eye. He also said any infected insulation and drywall should be thrown away as it absorbs the mold and it spreads throughout the drywall. It was his recommendation that you go one foot around the last are of mold found on a particular wall.

These are just his recommendations to me when I hired him for a consult on a foreclosed house that had the plumbing pipes freeze because it wasn't winterized in time and there was mold throughout the house.


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## Maintenance 6

Kilz is not and shouldn't be used as a mold killer. Use a fungicide. Kilz can be used as a sealer or stain blocker afterwards. Blindness would be an extreme and rare result of mold exposure. The vast majority of household mold related illnesses are allergenic in nature. Some susceptible people may complain of respiratory problems. And even those are not common in normally healthy people. Occaisionally skin irritations. Dry sanding an active mold colony is not something to do. Treat it first, Scrub it, then dry it. Sand it after that if you need to correct any surface problems for appearance. Then seal it.


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## M.D.

*I'm a new member with the Same mold situation.*

I am in a mobile home with what looks like the exact mold situation in one of my bathrooms. I've just had my bathroom linoleum pulled up and it looks like the pictures. The mold covers the space between the tub & toilet which are beside each other. I think it may have been a leak in the toilet that went undetected for some time. At one end of the tub/shower is a wall between my son's room & the bathroom where we 1st noticed some water & mild mold that seemed to be coming under the wall from that bathroom area. Now the room on the opposite side of the bathroom is beginning to show a long upward ridge near that connecting wall.
I'm not sure ,but some things , like the levelness of my double wide mobile home, has been affected by having moved the home from one mobile home park location to another. This is the time when I notice the ridge in the flooring of the laundry room (don't see any mold yet) and the mold which originated seemed to grow a lot more & rapidly. Also, the lot I was rented allows some water to get under the trailer in heavy rain storms.
I have virtually no budget to handle this so any input/advice would be greatly appreciated. I've learned some by your previous comments on this subject.

Thanks, M.D.


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## Blondesense

You've read several points of view in the previous posts. The only thing I would add is to make sure you take care of the initial moisture or water issues. Make sure any leaks are fixed and you have an adequately sized fan in the bathroom (and use it!), etc. If you replace the floor etc. but don't stop the moisture or water from returning you will get the mold back.


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## blueyes84

*black mold*

ok about black mold, its porus so it needs air,water and a feeding source...such as drywall or plywood, paper and other items. We live in Florida, and in our home we were going to put new wood flooring in. Until we found black mold, since then we rebuilt 20 ft of exterior wall and a complete rebuild of our 2nd bathroom. When it comes to bathroom flooring if you found mold along the edges and the floor is raised, its holding moisture....i would be guessing OSB board. I would replace it and paint it with a mold and mildew barrier before placing the toliet or anything. Make sure you use a roller and put two coats on....the first coat will fill cracks and any offsets in the plywood, the 2nd coat will seal it. I have dealt with cleaning agents, and ect. mold will return if its not removed and properly prevented. When you pull up the flooring examine the floor joices. On the walls, i would use Green board, its sheetrock with a thick mold n mildew prevention barrier and its only a couple dollars more then sheetrock. i hope this helps.


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