New terrace wall efflorescence everywhere!

No, he says it already happened during storage! The second picture also shows the stone stacked before installation.

Although one might wonder why the material was knowingly installed that way...

Kärcher?

I say naivety... The stones were parked at the dealer for 2 months, where after about two weeks the stones changed like this... took pictures and asked what that was... Answer, it goes away through weathering. My impression was that concrete dust got wet and just ran down the stone, but it goes away with water! I didn't google, no info on what can happen with such stones... The shock came when I wanted to clean the stones at home, of course already installed... I just completely trusted my local dealer

the concrete dust got wet and just ran down the stone, but it goes away with water!

Hello Schnubbi

that's exactly the situation. The air was full of dust and then it rained a bit. The concrete ran down and then set.
Wire brush, water and strong arms. Then the issue should be resolved. A pressure washer would also be possible, but it damages the stone.
Try it first on a piece of wall. Let's say four stones. Wait a few days. If it works: have fun scrubbing.

Steven

Hello

what I notice: The format of the stones in the wall looks different from the format of the stones on the pallet. Is that an illusion?

Steven

the picture with the stones on the pallet is probably from the short side?

When you enlarge the picture (the quality is great it looks to me
as if something ran onto the top row (not from inside over the
edge but on the edge!) And only from above. The streaks can clearly
be tracked from top to bottom.

Maybe there was still something on the (over the) pallets at the dealer?
Scraping off and chemical examination? Then clarity.

If this is something that should not be in or on the stone (belongs according to the manufacturer)
it is something "foreign" for which the dealer / supplier should take responsibility?

They were loose, can only come from the stone itself... I will get to work right away and report. There is the format with 3, 2, and one compartment to fill. .. on the pallet, there are still full stones to be placed as the finish (top row)