Hey Glenn, I recently finished a patio behind our house. I didn't use flagstone, I used a product called a Walkmaker by Quikrete, basically a mold you fill with concrete to get a random stone pattern, but the end result is wide joints similar to what you'll have between your flagstones. I found a product called Envirostone made by Envirobond. (www.envirobond.com) It's similar to the "stabilizing" sands you've seen, but is specifically made for flagstone joints. It is a mixture of a fine sand, aggregate, and their "stabilizer". It's been raining here everyday since I put the Envirostone down and swept it in to the joints, so I still don't know exactly how hard it sets up, but it is very tightly packed in from the rain and isn't running off at all. I imagine once it dries it will not blow away. I did fill my joints about 50% with pea gravel before adding the Envirostone to keep costs down. The Envirostone was $12.50 a bag locally, and I needed 4 bags of it for my 225 sq. ft patio. I also used 5 bags of pea gravel. They have 2 colors of Envirostone, I used the "natural", sort of tan/beige when dry. Here are a couple of pics of the finished patio. Good luck! http://img201.echo.cx/my.php?image=patiodone10lm.jpg http://img141.echo.cx/my.php?image=patiodone31xz.jpg

I am guessing that you live in a climate that has multiple freeze/thaw cycles. everything moves with the weather conditions - expanding and contracting. additionally, if water somehow finds its way into the mortar or stone, it could expand when frozen and aid in the hairline cracks in your mortar. I would repair the joints the best I could, adding a liquid latex (B-20) to the mortar mix. this will allow more flexibility. then I would seal the whole thing with a waterproofer like: "Gloss n' Guard" or "Weather Seal Siloxane" this will keep the water out of your flagstone and joints. Belden Brick and Supply Co. in Grand Rapids carries this stuff if you are interested. they may have more answers as well!

Would try and discourage you from installing flagstone, especially with mortar, over a patio that is cracked and separated. If you mortar and the crack widens or deepens it will cause separation of the flagstone above. If you mortar or glue just the edges and set the middle in sand it may work for a short time but will almost assuredly disappoint you later, with the same 1/4 section that is now sunken, progressing in its failure. The 'best practice' in this situation is to fix the underlying problem which is the existing patio itself. Fixing probably means removing the patio and re-pouring a new one before you would apply any material topically. Good luck!

I’d call the handyman and ask what specific products were used, then look up the instructions online. (I’d be curious to see if the sealer mfr recommends moisture testing prior to application.) I would assume they waited a week between cleaning and sealing to allow everything to dry out. But like I said before, that corner would probably take a lot longer to dry than the walkway, and if it was sealed before it was thoroughly dry, then either a. it’ll take forever to dry and thus lighten up or b. it’ll take forever to dry and the darkness you’re seeing is actually mold, not wetness. Keep in mind these are all just theories on my part. ;) Do you have before pics, by any chance?