I have exactly the same problem with a large area thermal bluestone walkway...1-1/2" dry butted joints, After the first season some of the stones began spalling to a point where the whole top layer about 1/8" would eventually shed off over time. The resulting surface is smooth again, but looks discolored and stained. Other stones have lost their color and look washed out. I have tried different types of stone cleaning agents to regain some color but to no avail.

From my preliminary research on bluestone, i guess there are different density grades depending on the batch that was quarried. This combined with the freeze thaw cycles in the NE seem to be the possible culprit. The stone yards have no clue when I address this issue to them and they have no clue what type/quality of bluestone they are selling. So my multi thousand dollar walkway looks like crap and I have to see it several times a day. I don't know if replacing some of the stones is worth the time and money if this will only continue to happen again and I am not sure how to purchase/specify stone that is less likely for this to happen based on the lack of knowledge of most salesmen. If i had to do it over again, I would have used a bluestone-like concrete paver.

My contractor was also perplexed and was giving me the old "stone is a natural substance with imperfections" BS. After his 2 failed attempts at making the appearance acceptable (scraping and burnishing), he is still willing to work with me on this problem up to and including some stone replacement....but i need to know if there IS? a solution?

Did you ever get a resolution to this problem? Did it get worse? We have the same problem with our patio in Bronxville NY

I have Asian Bluestone on my covered porch. This stuff started powdering up and flaking off within the first year! The rock dealer tried to tell me that I put "something" on it to make it do that! After a fight, we had them take out 90% and replace with new tiles. One year later, they are doing the same thing! I hate it. I want to rip it all out and put in concrete!

Did you find a solution or cause to the brown/discolored spots?

Same with discoloration. Also Bronxville ny

Deicing salts on bluestone causes this too

We had a bluestone patio installed at our moms house in long island. This is one of the dpalling stones. I would say this is NOT Pennsylvania Bluestone but an inferior import. Ask your stone yard for the vendor or quarry where they get their material. These supply yards may be bringing in cheap material.

I agree with riccardino but you have to realize natural stone is natural at the end of the day and im a 3rd generation Pennsylvania bluestone quarryman if it turned black whoch we call that black jack it had calcium deposit on it which we would never send to a customer but the brown means there is iron in the stone which we cant see when we produce the stone but i know most our buyers tell their customers to seal it to protect this from the minerals coming out and doing this.