Concrete mortar in flagstone patio?

[hitekcountry]

What it comes down to is that a solid grout without a solid base to lock the stones in place, is asking for problems. And a moveable base requires a flexible grout, but you want one that doesn't wash away or blow around. Well actually there is such a thing, but I don't think I'd recommend it for your application. There is a highly flexible material that's used to seal the joint between a concrete deck and the copping around the perimeter of swimming pools. That gap is essentially an expansion joint that allows the swimming pool and the deck to expand and contract independently. That gap then needs to be sealed to prevent water from pouring into the gap. The difference there is that those gaps are fairly consistent and generally less than 1 in width, where your "grout lines" can be several inches wide. The other important factor is that the stuff is extremely expensive. Thought I let you know about the stuff, but I'm not sure it's appropriate for your application.

 

[riptides]

I ended up using a "stone" dust mixture that was also used for the base to fill in. Our patio is around two years old, and every time I frequent it, it gets beer.

The beer encourages moss to grow, and I'd say about 1/2 the 300+ square foot area is now "sealed" with moss.

I obviously need to drink more beer and expand my area of coverage.

Moss is a very clean option, and very low maintenance. It holds up well in a high traffic area of our patio too. That being around the grill.

 

[Egon]

Moss is a very clean option, and very low maintenance.

Does that mean Moss brings his own beer??