This is my first house and I've owned it for almost 2 years. I think I have mold in the basement, but I'm not 100% sure. Here's some background on my house.

My basement floor is about 6 feet below grade. The walls are made of cinder blocks. The blocks were painted white, but I'm not sure if they used Drylock or regular paint. We have a high water table in my neighborhood and I do have a sump pump. A few weeks before I bought the house, the town was flooded. There was a small, thin covering of water on my basement floor... perhaps 1/8 of an inch... 1/4 inch in some corners. The sump pump was working at the time. Since then I have completely redone the sump pump and basin because the morons who installed it only made a 1 foot cube basin that they bricked and mortared!! During the spring, summer, and fall I keep a dehumidifier running almost 24-7.

I have concerns about 3 of the 4 corners. These corners just happen to be where my downspouts are outside and when it rains badly and the river floods, dampness used to occur here first (I've had no problems since I fixed the sump pump). I have adjusted the downspouts and will be installing a french drain around the inside perimeter of my foundation below the floor in a couple of years to direct water to the sump pump.

Again, I think I have mold in three of the corners. Attached are pictures of the worst spots. Is this mold? If so, how bad? Is the removal something I can do or do I need to hire a professional? Any idea how much removal costs? Any and all advice is welcome.

Thanks... Logan

Logan, sure looks like mold. Flick a small amount of household bleach on it, if the flecks turn soft brown after a few minutes it is mold. Clean with a mildewcide that can be bought at most home center. Some folks just use a 1:4 mix of water to fresh bleach.

Just to clarify, that's 1 part water 4 parts bleach?

Be sure to have adequate ventilation when you are doing this procedure as well.

Check how far away downspout pure water?
It needs 5 feet away from your house.
Downspout is not connected to storm or sewer line, is it right? Because it can be 2 different solutions to stop that mold. When you see signs like this you will need to stop that leakage first. And then clean walls. Otherwise your brickes will be wet amd mold wouldn't go away.

Logan, turn that formula around, one part bleach to 4 parts water, I wrote it wrong, sorry.

Update:

I tried pouring bleach over those spots but the color didn't change. I still think it's mold, but it appears that the people before me painted over it.

Is it possible that if someone has painted over mold and the mold is growing between the coats of paint? If so, how do I tackle the job?

Logan76,

Is it still dark? Is it not getting any lighter? If so you have to make waterproof outside (best solution), if it is getting lighter it means your walls are getting dry (water stop coming "in"). Get hard brush, put mask on your nose(!) and clean mold away, let it dry completely and if no signs of water you can put new coat of paint. But also you can make some inside protection (hydrolic cement can be put as a layer to your walls from inside, that cement will make a waterproof protection and nothing will get out from that layer, we use that trick when we need double protection. The first option, of course, outside dig, installation of weeping tile (or you call that french drain), connection to sump pump, layer of Blue Seal, and then membrane on top, full outside protection for your walls to get rid of outside ground water.

Inside it can be bleached (as you did) just to kill bacteria, clean out, cemented (by special type of cement - hydrolic ot water instant plug cement), painted. This option is going to work only if you will stop leaking from outside.