Recommendation for Austin limestone cleaners. (Plano: appointed, new house, school)

[slk750]

Howdy,
I recently turned a home owner and need some help with home maintenance. My home exterior is Austin limestone and I have noticed black coloring on the areas exposed to rain. I believe this is dirt/pollution/algae. There are lots of suggestions on using power washing/pressure washing/chemical treatments, etc. I tried to use an electric pressure washer but did not get the expected results and I am not comfortable with using chemical cleaners being a first time home owner. Wondering if anyone had used a professional to get this kind of work done and would provide your recommendations?

Appreciate your time and help in this matter.

[EDS_]

We have a good bit of both Austin Chalk on our house and Oklahoma Flagstone around our pool and spa. Ditto at our last house in Plano.

Easy:
I use bleach (3 parts hot water to 1 part bleach) in a spray bottle or small spray tank. Works great for me. When done hose down that area and all plants and grass with copious amounts of water from a hose.

Not easy but sometimes needed:
A weak muriatic acid solution will clean the stone while removing a thin layer of the stone. If you haven't done this kind of thing before consider it a pro only job. Pool companies clean flagstone pool decks this way all the time. Muriatic acid (it's really just weakened hydrochloric acid).......fumes like crazy, ruins clothes, kills plants and heavens forbid if you got any in your eyes.

Easy but you've got to have the right equipment:
A hot water power washer can work. But you'd need pretty serious machine. Further, a pressure washer spraying a combination of water and an abrasive (epson salt, properly milled aggregates etc.) will work for certain.

I don't know but I'd guess plain old soda blasting (dry soda) would work as well. Heck old school sand blasting would probably work.

Good luck.

[turf3]

Don't know if you have an old or a new house with Austin chalk. My almost 80 year old Austin Chalk house has all kinds of neat little fossils visible. My parents had it power washed and it damaged a number of the fossils, which I was very disappointed in. But they had no appreciation for anything old or with patina. They also cut down a couple of 50+ year old trees so they could grow grass better.

Anyway, if you have fossils in your stone, be advised that pressure washing, abrasives, or acids are likely to damage or destroy them.

I would suggest you consider the darkening of the stone as patina which adds to the character of the house.

[slk750]

Thanks EDS_ and turf3 for your inputs.