I'm about to demo the old deck in my backyard, and I plan to lay a flagstone patio.

I've visited a couple of stone suppliers and I think I'm going to use 1.5" stone for the 16'x 16' section. What I haven't figured out is what to use as a base material, and what I'm going to use in the joints.

The easiest route seems to be using decomposed crushed granite as a base and between the stones. However, I think I really want to bond the joints with some type of mortar. If I bond the joints, what base material should I use and what should I use between the joints?

Any advice is much appreciated!

sand, lots and lots of sand.

you need about a 3" base laid, skreed it level with a 2x4 and runners (2x4 laid flat and leveled, skreed to that by running your 2x4 in a saw motion on top of them) then compacted, rent a vibrating packer from a rental yd. compact damp (not wet but just damp so it will hold a ball when you compress it in your hand). should end up about 2" or a little less. this is important for drainage and leveling.
lay your stone with tight joints, when you get done throw more sand on and push broom it into the joints, repeat till they are full. get some osb or even clean used plywood, lay 3-4 sheets on top and vibrate again, repeat till the sand will not go down anymore, spray water and be sure to soak all joints well, repeat sand till compacted well and no more will go in.

should be some youtube of how to do it this way. buy some advil, lots of advil as your back is gonna hate ya for a week or two.

If you want it to last follow Hop instructions with these exceptions. Use a few bags of dry cement in the sand. Dig the pattern out about two inches deep and fill with sand ans concrete mixture. compact with tamper. Add another 1 2 inches of sand and compress again with tamper . Lay your flag stone in the pattern you want. Once finished use the color of decomposed crushed granite that you want to fill the grout lines. water lightly and repeat. Sweep clean and allow to dry and seal

The 2 posts above explain it perfectly. For the stone surface joints, you might also consider Quikrete PowerLoc jointing sand. It's a polymer based sand made for this application.

y'all are more up to date on the new materials, been at least 20 yrs since I laid any pavers, my back still hates me for it.

I forgot about the portland cement. gettin old ain't for sissies. lol

I had a pool built 15 years ago, surrounded by flagstone. They poured concrete slab and then laid flagstone. It looks as good today as it did then. I got the idea to do it with sand.....it cracked within 5 years. I added more using concrete and it has been ten years and still looks new. FYI

I for the most part follow what Hop and Bruce mentioned. Something I add when constructing paver or flagstone patio without a concrete base is a 4" crushed roadbase base layer due to our black gumbo clay soil. Use a plate compator on the roadbase and get semi level. The road base layer is topped with a 2" sand/cement mixture. Screed using 2x4 across 3/4" pipes leveled as guides.

I make what I call runways which are 6"-12" wide rows of sand the entire length of the area I will be screeding. Put down the 3/4" pipe and level it to your liking, I normally pitch it one direction for drainage. Once the pipe is leveled, Start wheel barrowing/shoveling in your sand. Screed the area and start laying pavers or flag.

Polymeric sand will work great on your joints if they are less than 1/2" wide otherwise use whats called gator dust. Sweep into joints and wash off with water which sets the polymer in the sand to bond the joints together. Make sure and wash off any excess polymeric sand or will bond to the top of the flag.

Here is a pic of my flag patio that was built like mentioned. It's 7 years old and holding up great.


Here is a in progress pic of a fire pit and patio using the same method. You can see the roadbase and sand. I should have taken a pic of us packing and screeding the project. I also set the soldier course (outside row) in concrete if I'm not bordering another patio. This stops the outer row from breaking away and falling apart.


Final product.I just finished washing off the polymeric sand.

Here is one like you're wanting to do. Smaller area than you mentioned but it's one I set the flag on a bed of concrete. Excavated 6" deeper than sidewalk/driveway then filled with concrete as we went. We used 2" flag so basically 4" of concrete. Once it dried, I mortared the joints. You might want to add some rebar to an area like you mentioned.

Pour concrete patio, buy 3/4-1 inch flag stone and set like tile then grout the joints.

I already have the patio poured, 16x20, my winter project is doing the flagstone top

I did what hop said, but I got pissed that my "seams" never seemed to set. So, i poured sacrete all over everything, swept it off the stones, and watered. Kept sweeping so no dust was on stones and it was great when finished. I would do it again this way.

That looks great!

Nice work