Basement floor problem - water, mold, stain

[ausername1]

Had a window that was leaking for a few months and I didn't notice bc I had a lot of boxes in the way. A large area about 15' x 5' was completely soaked, had mold, etc etc... So, I cleaned with bleach and scrubbing, wet dry vacuum and then tried vinegar on the white areas thinking it would cut the calcium/hard water stains. But, the vinegar didn't do anything even after more scrubbing / rinsing / vac... Now, I've stopped the water source, used a leaf blower to try and help the drying process and have let it sit for a week or two.

But, it looks terrible and I'm thinking these are my only two options.
- Paint it with Kilz garage floor paint
- Power wash it and scrub and bleach again and then see if it the stained area will get removed

The dark area is dry to the touch so it's like the concrete is permanently stained now? I'm guessing power washing will remove the white stains (which are what exactly? vinegar didn't help them so maybe it's not calcium?). But, I'm worried that adding more water during power washing will make it take several weeks or a few months to fully dry.

It's been at least 2 weeks since I cleaned it last and dried it and the dark area hasn't gone away or reduced in size. I'm thinking just a light cleaning with not a lot more water this time and just paint it is the only way to save it?

Thanks for any thoughts.

[machinist]

Hi! Welcome to the forum!

The dark areas are likely moisture stains or remnants of mold, while the white marks could be efflorescence, which happens when water leaves behind salt deposits. The fact that vinegar didn’t do anything suggests they might not be typical hard water stains, which can be tricky to remove.

Since it has been two weeks and the dark area hasn’t lightened, the moisture may have penetrated deep into the concrete, making it a permanent stain. Before painting over it, you might want to check if there's still moisture trapped inside. One simple way to do this is by taping a plastic sheet over a section of the stained area and leaving it for 24 hours. If you see condensation underneath, then there’s still moisture in the concrete, and it might need more time to fully dry. Using a dehumidifier, fans, or even a space heater could help speed up the process.

For the white stains, since vinegar didn’t work, a stronger cleaner like a commercial efflorescence remover or diluted muriatic acid might do the trick. If you’d rather not deal with strong chemicals, scrubbing with a dry cleaner like TSP (trisodium phosphate) could also help lift the residue. As for the dark stains, a good concrete cleaner, an oxygen bleach solution, or a degreaser might be worth trying before resorting to painting. Power washing could help, but as you mentioned, it would introduce more water, which means more drying time.

If the stains won’t budge and the floor is completely dry, painting it with Kilz or a similar concrete paint could be a good way to seal and refresh the area. Just make sure the floor is fully dry before applying any paint to avoid peeling or adhesion issues. Given how much work you’ve already put into this, painting might be the quickest and easiest way to get a clean and finished look without spending more time scrubbing.

Machinist.

[ausername1]

Ok, thanks for the excellent advice and info!! Alright, let me see if I can determine how much moisture is present then I'll make a judgement call. Thinking in the end I'll have to paint.

[machinist]

You're very welcome! Glad we could help. Keep us posted on what you find and how the fix goes. Would love to hear the outcome.

[ausername1]

Well, I just dried some more, cleaned with a towel/sweep and painted it.... Twice. And, looks good enough... You can see the imperfections from the buildup that wouldn't come off with scrubbing but only just barely. I just didn't want to powerwash it and make even more wet. I think I could have removed those buildups that way but it might have taken literally weeks to dry. Don't have time for that. Thanks for the help!

[machinist]

The results look pretty good. Those subtle texture variations and the little crack are totally normal, by the way. They actually give the floor a bit of character. Glad it worked out for you!