Performing a building wash and having trouble with a growth? on cast concrete. Treated with multiple coats of 4% and surfuctant to clean brick and this removed most of organic from cast concrete.
What’s left is something I’ve yet to come across. It’s black, raised and seemingly impervious to SH. When the building wash failed to remove, I treated with 10% + lye and still nothing!
Put high pressure on an area that had undergone these treatments as an experiment. The black came off with some work and left raised bumps of concrete behind. Thinking it has been there so long that the concrete around it has been worn from weather and these areas remain at original height? Building is approximately 60 years old and probably never cleaned.
Is this organic? Can it be removed with anything short of high pressure? Thanks in advance.
This whole area was sprayed with higher concentration, the leading edge just seemed to clean better. This view is from the roof, not actually visible at all from the ground. Some of the black is visible from ground however.
The second photo in my post shows cast concrete that actually underwent multiple treatments at 4% and then 10% + lye. Close ups only had 10% + lye and selective pressure.
Is it a flat roof with a rolled rubber roof coating, with possible gravel on top (river stone etc).? It is possible that the roofers left some tar up there
On further inspection it doesn’t look like tar. Try a turbo on it?
I was thinking the same thing as dirtyboy. Looks like remnants from asphalt from the roof. Is the top the only place that has it? If you think it’s organic use 12.5% straight sh. If you think it’s asphalt or tar use a good caustic degreaser. It could’ve be the sodium hydroxide doing the cleaning. If so, you’re better off with a degreaser and amping it up with the sodium hydroxide.
12.5% + s hydroxide still didn’t touch it. I think that disqualifies it as organic? The building turned out great, finishing up with windows today. I don’t intend to pursue this mystery black stain any further without talking to building owner as it doesn’t appear to be organic and so, is outside original scope of work.
Thanks for that. The property owner is thrilled with the results but I must admit I’m curious to know what would remove it. When I have some free time, maybe over the winter, I’ll try that and some of the other suggestions.
