Black wood on patio ceiling, shouldn't be black


An elderly family friend has a 3200 Sqft house. She states every time she has someone wash it her patio ceiling black mold comes back within two months, which may or may not be true. I have attached some pics. It appears to me that maybe the guys washing previously only used high pressure water???

Being that the ceiling front and back is going to be the hard part, I am thinking of some roof snot/cling-on to help get the chems to stick to the ceiling for awhile. Any recommendations for a mixture other than a stronger HW and let soak in? Percarbonate or Ox? It is painted white but the mold has definitely penetrated and there is no UV that hits it. Straight up embedded mold form years and years.

She is at her wits end paying guys when she says it never works. Any assistance so I can help an old friend would be great. The rest of the house is straight forward and I’ll just water down the plants a bit since its overgrown next to the house.

I am down streaming with a 10:1 injector with 12.5% and Gain. HW varies between 3:2 and 4:1 SH/H20 depending on application with this injector.


Picture didn’t upload. Try again.






If they sprayed bleach on bead board that had a poly finish, it will turn black.


If you aren’t confident, do a small test spot with a similar mix that you’d get while downstreaming, but in a pump up sprayer. Drop the gain, get some Elemonator and don’t forget to bag the fan before you wash it. I’m still a newb so if someone disagrees please say so. I think downstreaming should work just fine.

1 Like

Cleaned and then re-painted would be my suggestion.


Mold is having a feast on the ceiling AND moulding. Then it stops abruptly at the yellow paint. Definitely looks like defective paint or wrong paint product. Maybe somebody figured it wouldn’t get rained on and slapped an interior ceiling paint on there.

1 Like

I’d listen to them before myself btw ^^^


I will ask if they know if there was a poly finish applied.


I will temp her expectation from cleaning and recommend she may need a painter to strip and refinish.

1 Like

Definitely just use 12.5 percent and elemonator. A few applications and long dwell time. With it not being in the sun, let it dwell while you wash the back side of the house and one side. That’s what I would try. I love challenges and I would take this on in a heart beat. Elemonator and SH will hold off mildew a lot longer than just high pressure which is what it looks like. I would also offer to do that part for free if you are just doing the whole house anyways. That literally would take not even 10 minutes of dwell anyways. That way if it doesn’t work then you can suggest to her it’s at least clean for paint. Tell her it’s a 50/50

1 Like

That sounds like a good plan. Elemon on the way.

Anyone with experience with oxalic acid h2o mix for rust on wood siding? Their well water sprinklers make big rust stains.


Issue is some one painted over the mold before cleaning. When it gets cleaned it can’t kill the mold behind the paint, which bleeds through after a few months.


Yes, it sounds like she and her husband did. She referenced painting it with Kilz, which indicated to me that they rolled over the partially cleaned mold.


While it looks great now, interested if it holds better than 2 months like she stated.

This hardi board house was difficult. Multiple deep rust stains on every side. They have been using iron out to remove the rust which has created large white spots on the paint.

First hardy board house and I read a lot so I reduced the SH and washed within about 2 minutes. If any paint issue occured it was not noticable in part because of pre existing paint conditions.
The porch ceiling took 2-3 applications with 8-10 minute dwell times to come fully clean.
2-4 applications of 1/2 cup OA to 1 gal h20


Nicely done


Looks great! If that mold starts to come back even after you cleaned it. Tell them to mix up a squirt bottle of 50/50 white vinegar and warm water to spot treat it with. Have they checked for leaks? Thats horrible.