Anyone built a flagstone patio? I put stones down last year, didn’t get it all finished so I covered for winter. Just pulled the cover up to start finishing it, looks good a couple are tippy and need a little sand under an edge or something. My question is what polymers sand to use between the joints. I’m leaning towards Techniseal NOCO Storm Multi-Weather Jointing Compound. It is a sweep in with water type filler. Kinda expensive, just hoping it last a while. This is about 450 sq. feet.



wws

I like it a lot!!!

Looks real nice!

I used irregular concrete pavers that are supposed to interlock, and they do...sorta...I'll get 6 of them to fit and I'm stuck, lol
I finally put them reasonably close together and filled around them with sand, being we live on a sandbar, sand is free, lol

I wouldn't have the patience, and probably the ability to do what you've done....so I'm no help..

not specifically flag stone

brick and other styles of paver yes

ideally you compact with a vibratory compactore , you have pieces of plywood to lay over the brick or other stone , the vibration settle the stone down into a base of crushed limestone so that it doesn't get tippy or less so any way.

My wife like collecting river agates, I figured a few of the spots that have a bigger gap will throw a polished river agate into it. Be little treasures for the grandkids to find. It was a fair amount of work, just hope it last. I have almost a foot of crushed rock under it all compacted. Need to get this done, irrigation in, grass, all done so i can go fishing. Wife wanted a yard but I bought a boat. Now she gets her yard. Thank you for the compliments.

wws

That looks great! It is a real test of patience fitting natural stone. As for your "grout", I'm not sure how it will hold up with the stones not on a concrete or similar base. The material under the stones WILL move over a short period of time, with wet-dry-soil compaction, freeze/thaw, all of which will result if the individual stones moving. Even a little movement will result in cracking. I have used play sand before when using bricks, but the gaps were very small, less than 1/2", and even that needed re-doing every year or two. We used sand a couple years ago for our 12"x18" paver walkway here in southern Oregon. I put a 1-1/2" gap between each paver but the squirrels keep digging it out trying to hide peanuts, so will be replacing that with dirt and then grass seed.
You might look into using very small pea gravel, the 1/4"-3/8" stuff. Washed pea gravel would sit in there nicely and probably look great.

Looks like a lot of work, but sure will be worth it when it's done. Looks great!

Pea gravel sounds good but it migrates everywhere, I have a pea gravel yard and it gets over the pavers of the walkway and you constantly need to sweep them clear....and sand doesn't really pack down very well....maybe a crushed stone, a mix of dust and small pieces that should mesh together and pack down....

Techniseal recommends a free draining base under NOCO storm. They also make a dry version of NOCO for dense graded base. This product sweeps in dry and you wet it afterwards to activate.

Tecniseal has a very good reputation and is a good choice. Call them, tell them what the flagstone is laid on and where you are (climate). They will point you in the right direction. The resin based NOCO storm is a very good choice.

I have also used a product called perk grout. It is mixed and applied like mortar. Flagstone patio on dense graded base. Tedious to apply but looked good when done. Did the work in 2023 for one of my pickiest customers. Spoke to her a week ago and no mention of a problem. This means the product is performing very well.

Wet applied jointing material is resin based.i do not have much experience with them. I have recently started using them when I can because they last longer. That said, I suspect they would be a nightmare to rejoint.

Dry applied jointing sand is polymer based. I have quite a bit of experiecce with these, mostly pavers but some flagstone. Very much a love hate relationship. There always seems to be that one spot that never sets right. Resanding takes some effort, but is doable. The polymer degrades over time (3-7 years in MN). On wide joints in flagstone I have used Alliance (Gator Dust), Polysweep and SRW with poor results. I have a flagstone patio rebuild on the schedule for this year. I will be using the techniseal dry applied NOCO sand for this one due to its great reputation for flagstone on dense graded base.

Traditional jointing material like sand or gravel also works. It is easy to work with and easy to replace, but it moves alot. It will end up on the flagstone surface and plants will grow in it. The joints are also less chair friendly. This is my go to on walking paths, but not so great for patios. If you go this route, make sure to use an angular/crushed material. It packs in tighter and moves less. Rounded aggregate like pea rock and some sands roll/move too much .

That is about everything I know about jointing a flagstone patio.

If the pictures above show your first go at laying flagstone I am a bit humbled and quite impressed. I will be stealing a couple of your design elements. Top notch.