Hey guys I’ve researched thoroughly via this forum and Youtube videos and decided to pressure wash on a section of my concrete.
I batch mixed about 4% SH and surfactant as a pre treat and let it dwell for about 5 minutes. After my first rinse i still had a large amount of black mold and mildew i believe.
I was irritated at the results and tried it again with a hotter mix at 6% and let it dwell for roughly the same time. The spots wouldn’t go away. I decide to use my green tip and managed to clean most of the spots but I believe I etched my concrete as pores started showing and the aggregates within the concrete.
Just spitballing a thought here - perhaps the pits are basically filled with mold and being small holes the surface cleaner is not able to force the mold out of the hole. I would suggest a longer dwell as a first possible solution. With the holes so small, I am not sure a surface cleaner would ever flush out the mold without keeping it in one place which might risk leaving circle marks on the surround concrete.
It is kinda like cleaning exposed aggregate concrete that is basically a minefield of gaps and valleys in the surface. I find I have to go slower or multiple passes sometimes to fully clean it.
Post treat it and check it again when it has dried. Sometimes there are black spots that dont disappear immediately if at all. I tell the customer Ive used adequate pressure and any more will start to remove layers. They understand, but a dwell, post treat, and drying may be needed.
A five minute dwell time isn’t very long. Make sure you get plenty of SH down. If the concrete is warm it’ll dehydrate before it has a chance to work. Sometimes you have to get it good and wet and keep misting.
I get that all the time in really bad concrete here and a lot of times it’s not very apparent before you surface clean. Post treat with a hot mix with a dedicated sprayer, plan on hitting it multiple times and it will usually come off with the wand once it has changed colors.
I ran across some of this the other day on a job, I have to go back and Fix it, but it seems the only thing that works is high PSI with a and really close up.
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