Laying Flagstone

As a material, flagstone is cut or "flagged" by separating the "layers" or stratifications of rock formations. The primary rocks used for this are limestone, slate, bluestone, and sandstone. The quality and color of these stones vary and these variances often become a retail pricing factor.

The hardness of the stones is important when choosing them for certain projects. Slate generally is the hardest of the flags and it is non-porous. Color ranges are green, gray, and purple. Limestone varies both in hardness-from dense to granular; color is widely varied: you can find lots of tones. Bluestone and sandstone range in color from a light beige to pink to red to a dark bluish tone. Both stones are fairly soft (as compared to slate) and are easy to cut.

MEASUREMENTS & MATERIALS:
Most retailers sell flags by the square foot. And many retailers let you pick out what you want from the pile. Therefore, you ought to know approximately how many square feet of the material you'll need for your project, PLUS about 10 percent for sizing and shaping and waste. You will fracture some stone the wrong way. If possible, try to "pre-fit" the flags as you select them. Lay each piece down on the ground and try to match the pieces as they would go together. You'll be a bit sloppy doing this; the idea is to approximate matches so you'll have less cutting to do later.

The project you are creating with flags will also determine other materials. If you will set the flags on bare ground (in a warm, nonfreezing climate), the thickness of the stones should be a tad more than if you will set the stones on a sand base. If the stones go on a concrete base, they can be thinner because the concrete will support the thinner size reducing breakage from weight on the stones' surface.

It is next to impossible to figure the amount of cement and sand needed for setting flags, so we'll give you a rule of thumb: buy 160 pounds of Portland cement and 525 pounds of mortar sand for every 50 square feet, of flagstone surface, This formula will be just about right, although you may be a little short or long-a problem easily corrected as the job progresses.

STEP-BY-STEP:

1. With a brick chisel, score the flag where you want to fracture it. Just tap along the cutoff line with the chisel until it forms a "notch" in the stone. Wear gloves and safety glasses.
2. Lay the flagstone over a piece of 1x2, aligning the notch you cut in the stone with the edge of the 1x2. Then lightly tap along the notch with a sledge or rubber hammer to fracture the stone.
3. After fitting and cutting the flags, set them back down on the sand base and tap them into firm position with a rubber or wooden hammer. Leave approximately 1/2-to 3/4-in. at joints.
4. Level the job as you progress with it. The flags should pitch slightly one way or another for drainage. If a flag is high, remove sand. If the flag is low, add sand. Test again for level.
5. When finished, sprinkle sand over the flags. Then, with a broom, work the sand into all of the joints. Sprinkle with water, fill again and again, sprinkling. Sand will "harden."
6. Over concrete, set flags in bed of stiff concrete. Then tap with trowel handle to level the flags. Work in a small area at one time and keep the flag joints about 1/2 to 3/4-in. apart.
7. Butter the stiff concrete after you set stones and lift them. Spread butter mixture with a trowel. Then reset the stones in the butter, tapping them lightly and leveling as you go.
8. Remove mortar from joints, using the point of a bricklayer's trowel, or, better, a tuck pointing trowel. Depth of johns should match the bottom of the flagstones so grout holds tight in joints.
9. Fill joints with grout mixture. Pack it in as tight as you can. Then smooth the joint with a concave jointing tool, smoothing the edges of the grout with the edges of the flagstones.