You’re welcome. 
Is there an equivalent of plant wash for acids? I’m not sure soaking would be enough for newer grass
Not that I know of… The grass will grow back. Just keep the edges saturated. I always have a forewarning to clients, that treatments may burn the edging.
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Maybe try a mix of baking soda and water?
That sounds like a good idea. Can’t be worse than killing it
Sheesh - it still looks better than it did, lol.
Few things - @Kentucky1234 rec for the baking soda is for the green stain on the rock, not the grass. No one cares about the grass. You put 2 coats of acid on and 2 inches of grass that wasn’t heavily saturated with water turned brown next to the edges. The first thing you tell the HO that may happen. But it’ll grow back in a couple of weeks. If it was edged they probably wouldn’t have even noticed.
You need to take control of the situation - The homeowner got a shoddy install by someone who left mortar smears and obviously didn’t put the sand down right. (Probably didn’t saturate it enough to get it thoroughly wet to full depth if he used polymeric sand). Honestly from looking at pic he may have just used mortar but you have to determine that. There should not be large amounts of sand coming out, maybe a little on the surface, but we’re talking a cup full on the whole patio if that. At least not from the nmd80. Not sure what else you’ve done. What pressure were you running on the surface cleaner? If you want to get more of it out then break out the turbo nozzle. But be careful, you take out too much with flagstone, not like just re-sanding pavers unless they’re set on a concrete base, you’re going to be re laying the thing. But in one post you say you want the sand out and in another, you say you’re worried about the nmd80 taking out the sand. If you can get it down 3/4’ to 1" then you can put the polymeric in and seal it and it should hold. Have you talked to the company that installed to find out what they used?
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The surface cleaner was around 1750 with 25 degree tips. The test area seemed alright. It took most of the sand off the stone without taking too much out of the joints. Of course now I believe otherwise. This is the only full treatment we applied.
To clarify, when I was cleaning the patio, I wanted to leave the sand in the joints. Now that the sand in the joints is damaged beyond repair, I need to remove the sand so I can reapply.
My first step is making sure I can remove the green. Then I’ll work on removing 3/4" - 1" sand like you recommend.
I have not talked to the installer. I will see if I can get their information.
Overall, I should be able to get through this. It’ll be a pretty penny in sand, and more lessons learned the hard way.
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I’m around on occasion…but don’t have time to read the whole thread. Whatcha need?
Alright guys and gals. Nature took care of most of the vanadium green staining. Baking soda helped out as well. I’m optimisic that the green will continue to improve.
New challenge… A lot of the red color that the customer likes was removed as well. It seems the red was more on the surface, and it got washed away along with the polymeric sand. Is there any way to restore the red? Is the red a product of internal iron? Could SH or another basic solution bring the red back out?
The first picture is the original stone. The second picture is the stone turned green on Tuesday. And the third picture is the stone today. The green was almost entirely resolved with time.
I was originally looking for your thoughts on removing vanadium stains from flagstone, but that problem is being resolved.
A new question though. Do you have any thoughts on bringing the red color back to flagstone that has been acid washed?
A mason told my customer that it would not be possible.
let it dry out for several days. Flagstone is pretty absorbent. Reason you generally want to seal it fairly soon after installation. Water can change the color and you’ve been drowning it for a week. Plus it’s stone. Changes color some anyway. You need to get out of there. The more I look at it, I think it’s mortar joints. Look at the pic of the big piece in upper left corner looks like a pebble or coarse sand in that joint. Typically that’s what is used here and most places. You use a thick mortar and then use like a whisk broom to sweep away mortar off of edges. Probably why it had so much sand on the surface.
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I’ll let it dry. I’m asking for more time, but I’m afraid it’s heading toward an insurance claim.
Think of it like acid washed jeans…it’s almost like bleaching a color. My only thought is how far did the acid go down? If it’s a super thick rock perhaps it could be sanded past the acid discoloring? It’s just a thought.
I’m working on a quote for some stones and flagstone. Not sure what kind of stones they are.
For some reason this thread has stuck with me.
The green is algae…not the color of the stone.
I’m thinking SH but just want to make sure I don’t end up in sixsolve’s bind (sorry, bud) so I’m double-checking with you all.
Am I thinking right?
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Hey man, yes, you’re right. SH will take care of the green algae no problem. Stay away from any acids on that colored stone and you will be fine. To set expectations, I would say the black streaks may not come out. I’ve had similar stone where the black just wouldn’t budge, and I’ve read similar experiences on here. If it’s black and on top you might have a good chance. If it’s black and looks like it’s inside/ part of the stone, I’d be surprised if you have much luck.
One more thing, take it easy with the pressure. That stone has a tendency to flake/ chip. You can also blast away some of the red coloring. If you see any flaking or any red running in the wash water, back off the pressure
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Thanks!
How did things turn out for you on the above job?
We resolved the dilemma with mutually agreeable terms.
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I use straight 12.5% sh on flagstone. Paint it on with soft bristle brush. I’m not talking about down streaming either I’m saying full undiluted bleach straight on the flagstone. Once it dries the black stains typically go away.
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