Flagstone can be dry-laid on a compacted stone and sand base with sand or polymeric joints, or mortar-set on a reinforced concrete slab with grouted joints. Dry-laid flexes with clay soil and can be relaid; mortar-set is a solid surface that rides on the slab under it.
One independent, insured North Texas contractor will call or text within one business day to set a time to look at it. You get a written quote with the pattern, color, stone and slab spec on it.
Updated November 10, 2026
The stone, the base and the joint decide how it looks and how it holds up.
A trade write-up in the Journal of Light Construction walks through it: excavate about 8 inches below finish grade and 6 inches beyond the layout, add landscape fabric on wet, sandy or clay soil, place 5 to 6 inches of crusher-run stone in 3-inch lifts compacted to refusal, then a 1-to-2-inch sand bed that compacts to about an inch. Stones are floated in, and polymeric sand swept into the joints sets like a flexible mortar, resists weeds and still lets a stone be lifted and relaid. Pitch the surface about 2 inches in 8 feet away from the house.
Source: Journal of Light Construction, laying a flagstone terrace
A mortared installation sets each stone in a mortar bed on a reinforced concrete base, with grouted joints, which gives a solid, even surface and is the usual route when flagstone goes over an existing slab or at a doorway. One contractor guide calls for a 4-inch reinforced concrete base, compacted and sloped for drainage, and recommends sealing to keep water out of the grout joints. On North Texas clay, the slab is doing the structural work and should be quoted like any other 4-inch slab: steel, base, joints.
Source: Landscaping Network, flagstone installation (dry-laid vs. mortared)
Natural-cleft bluestone pavers are split to 1 to 3 inches thick; stair treads run 2 to 6 inches. Thicker stone resists rocking on a dry-laid base; thinner stone is fine in mortar on a slab. For a geometric layout the two rules of thumb in the trade are no seams longer than 6 feet and no four corners meeting unless the design calls for it. Irregular flagstone follows the opposite logic: tight, varied joints and big stones at doorways and steps.
Source: Journal of Light Construction, laying a flagstone terrace
Oklahoma and Arkansas sandstone flagstone in buff, tan and chocolate is the regional default and takes the heat well; Pennsylvania bluestone brings grey-blue tones at a higher freight cost; Texas limestone (Lueders and similar) matches the native stone on many DFW houses. Darker stone gets hot in July sun. Verify with the stone yard which quarries are in stock and ask for a pallet photo, since color varies by lot.
The eastern metro sits on Blackland Prairie clay that Texas Parks & Wildlife describes as black, calcareous, heavy clay over chalk and shale, and it moves with moisture. Dry-laid stone on a deep compacted base moves with it and can be reset. Mortar-set stone cracks with the slab under it, so that slab needs the same base, steel and joints as any other, and the joints should carry through the stone as grout lines. Ask the quote to state which method and why for your lot.
Source: Texas Parks & Wildlife, Blackland Prairie ecoregion
Stone steps are 2-to-6-inch treads on a mortared base or on block risers; a stone-veneered seat wall or planter runs on a small footing. Each of those is a line item with its own stone and its own base, and the quote should show them separately from the flatwork.
Source: Journal of Light Construction, laying a flagstone terrace
Dry-laid if you want flexibility on clay and the ability to relay a stone; mortared if you want a solid, even surface, especially over an existing slab or at a door.
Polymeric sand sets when wetted and limits weeds in dry-laid joints. Mortar or grout joints do not grow weeds but can crack with slab movement.
One to three inches for pavers; thicker stone is steadier on a dry-laid base, thinner is fine in mortar.
Yes, mortar-set, if the slab is sound and drains. That is one of the common uses of the mortared method.
Pattern, color method, sealer, stone and joint, or field thickness, edge, steel, base and membrane: one independent, insured North Texas contractor looks at the lot and writes it all down with dates.
Residential and acreage, in eight DFW counties. No price on this site, because the lot and the drawing decide the price.
One independent, insured North Texas contractor will call or text within one business day to set a time to look at it. You get a written quote with the pattern, color, stone and slab spec on it.