The following mold story has been selected to illustrate that it's easier to prevent mold growth than to clean it up after it grows. Take preventive action before mold starts to grow, because it will grow.
"Whoops, there goes a gallon of water over on the dining room carpet next to the wall. Oh no! What to do?"
I'm going to share with you what we did at a friend's house recently.
Quick! We ran for the towels. Stop the spread of water ASAP. You have to minimize the damage, because where water goes, mold will grow -- unless the area can be dried within 24-48 hours.
(As an aside, this scenario is yet another reason not to have carpeting. My friend would gladly get rid of the carpeting but, alas, her home has plywood floors underneath, and the installation of "green" flooring is not in the budget.)
As the water was sopped up, we followed the path the water might have taken to learn what needs to be done. First, we used a pair of pliers to pull up the carpet from the tack strips near the wall. We pull the carpet back so that we could feel the padding.
The padding was soaked, so we used scissors to cut out the wet portion. Mold cleanup protocols say that if padding is soaked, it needs to be thrown out, because it cannot be adequately dried. For us, entered the clothes dryer. We just popped the soaked piece of padding into the clothes dryer and set it for low heat. The padding dried out effectively over a period of time.
Next we felt the plywood. There was some water-staining on it. We were most concerned about the crack between two pieces of plywood, whether too much water seeped down through the crack and spread out under the plywood. Since concrete is under the plywood layer, mold could grow on the underside of the plywood if water was trapped between the plywood and the concrete.
We were hoping that since we acted fast and since the padding seemed to soak up most of the water, not too much water seeped underneath the plywood. We decided to let the plywood just air-dry for a day, and then I would check the area with a moisture meter.
(On the next day, the moisture meter registered "dry" for the plywood, plus the crack area. That was good news, because the alternative would be to remove the wet part of the plywood.)
We next turned our attention to the edge of the plywood, right near the base molding at the wall. Sure enough, water had reached to this area. I knew that the soft wood of the tack strips would be quickly attacked by mold if the tack strips didn't dry soon, so I got a screwdriver and pried up the tack strips. We stood them against a wall to dry.
Next, we looked at the bottom of the base molding. Did the water penetrate under that? If it did, that was another area that wouldn't dry out in time to prevent mold growth. The base molding had to come off. Again the screwdriver came in handy to pry the molding away from the wall.
We saw water staining on the inside bottom portion of the molding, which confirmed that removing the molding was necessary to prevent mold growth. We stood the molding against a wall to dry.
When the molding was removed, there was maybe a half-inch access to the sill plate. The sill plate is a horizontal piece of lumber to which the vertical studs are nailed to form a support for the sheetrock walls.
When I felt the surface of the sill plate, it was damp. I gave my friend two options: 1) We could either leave things as they were to dry, hoping that we caught the water in time so that not too much water penetrated under the sill plate and onto the paper backing of the sheetrock, or 2) we could cut into the wall cavity, removing the bottom portion of the sheetrock and opening up the area to dry better. A box cutter could be used to cut out the sheetrock.
After discussion, we decided on the first option, again hoping that we caught this spill in time to prevent any substantial amount of water from penetrating into the wall cavity. I explained that if the paper backing of the sheetrock got wet and could not dry out easily, it's a perfect material for mold growth.
Stachybotrys, the toxigenic black mold, particularly likes sheetrock, but it needs water to grow. If the surface dries off quickly, the mold won't grow. Stachybotrys likes the paper backing and also the calcium that leeches out of the sheetrock. Other common allergenic and toxigenic molds like sheetrock, too, such as Aspergillus and Penicillium.
So we crossed our fingers and hoped for the best. The next day, wood surfaces accessed within that half-inch gap were dry to touch. The moisture meter showed that the sheetrock was dry. Was it possible that a little bit of water was trapped under the sill plate? It was possible, but the risk was not worth tearing apart the wall.
My friend did not own a dehumidifier, or we would have run it in the area. In hindsight, we could have set up a fan. Dehumidifiers and fans can be used in the early stages of a water spill, before mold has a chance to grow. They should not be used without careful consideration later, after mold is established, because fans could blow spores about, and lowering the relative humidity can provoke mold to release spores.
Lastly, we propped up the pulled back carpet to allow access to air on both sides of the damp carpet. By the next day, the carpet was dry. The carpet was synthetic, which is more resistant to mold growth the natural carpet. Synthetic carpet has other downsides, but this at least is a positive. Natural fiber carpet and padding are at greater risk for mold growth, though not if they are dry by the next day.
We left the entire area open to the air for a second day for good measure, before putting everything back in place, starting with the piece of dried padding.
Considering that my friend's original intent was just to leave everything in place and "let it dry out" by itself, she's lucky that her environmental inspector was with her, for she surely would have had a big mold issue a week or two down the road.
That's sopping carpet padding would have contaminated the plywood subflooring, and the wet area behind the molding would have caused mold growth in those dark enclosed spaces.
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