HELP! Failed Acrylic Polymer Sealing of Sandstone Flagstone

[Shona]

Dear Do it yourselfers:
The result of our patio sealing by an installer is a disaster.
1. I just learned what the black spots are in sandstone: fungus....so now it's sealed in and I'm concerned I can't get it out.
2. A day or two after sealing, the polymer came up onto the surface of the stone and peeled and cracked, staying white (or didn't penetrate).
3. 90 percent of the stones (Cherokee red and pink sandstone) got discolored and stained with gray, brown and other colors which are NOT the colors of the flagstone.

So I'm guessing there was something in the stone that caused this, or failed polymer. My installer said this was the third time this happened this year. I wish he would have tested it if I was the third time!!!

QUESTIONS: What do I use to remove the polymer (other than dangerous chemicals like acetone, etc). I read some conservation articles and it seems that if one doesn't use dangerous stuff, it doesn't all come off.
2. Will the stain come off?
3. Do I need to talk to a chemist, or have my stones tested?
4. Can I get the fungus out of the stones after (if I can) get the polymer off?

MORE INFO:
Installer heated the patio with a crop burner (a flame) because the stones were damp and the sand joints needed more drying.
Polymer was applied before sunset in 50 - 60 degrees F.

THANK YOU!!!

I was told that the stones had 'acid' in them and that is what repelled the polymer. Not so sure about that.

I have photos if you need them.

 

[fixerupper3530]

Acetone will work to remove the polymer, but I would try an environmentally friendly paint stripper that can be put in a spray bottle and applied to the surface. FYI- you may have to rinse and repeat several times to remove it all. If all else fails, some have been known to use gasoline and a scrub brush to remove coatings. Once the polymer is completely removed try using a clear coat spray early in the morning with the surface being completely dry before application. Please make sure to wear a mask and gloves when you do this type of work.