Flagstone Options for Yard and Patio
A flagstone patio is hard to beat for durability and aesthetics, but not all flagstone is created equal. Here is a basic rundown of the range of flagstone options for building pool decks, walkways, porches and patios, and a host of other outdoor projects.
Flagstone is a generic word, not a geological term. It refers to the shape and aesthetics of landscaping rocks, and may cover a wide variety of stone types.
Most real flagstone is simply raw, quarried sandstone, a widely available sedimentary rock composed mainly of quartz and feldspar. Standard colors include gray, white, brown, red and pink.
Slate and limestone are less common sources of flagstone, but they may offer different colors than sandstone. Not all colors are available locally in all areas, so you may have to pay a premium for a specific color that matches your home and other landscaping features. For example, red sandstone is ubiquitous in the southwestern United States, but blue flagstone may be harder to find. On the other hand, so-called Pennsylvania bluestone (also not a geological term) is widely available in the northeast, but red sandstone may be a premium import.
All these three types of rock have rough, irregular and porous surfaces, which offer good traction, but also can lead to spalling (the splitting of surface layers when water or ice gets into the rock). Sandstone is least likely to spall. Also, most flagstone can be treated or sealed to reduce spalling. Still, stone must be chosen carefully in harsh climates.
Artificial concrete-based flagstone also is available. It is cheaper, and less likely to spall, and can be designed in virtually any color. However, it is also less attractive and less durable.
Flagstone is typically available in irregular shapes or in pre-cut uniform squares and rectangles.
Irregular flagstones are commonly used for casual, natural-looking patios. Both the surface and the edges are irregular and rough-cut. Prices vary widely around the country, but local rock is available nearly everywhere, and is typically cheaper. Irregular flagstone is typically sold by the ton. Pieces smaller than 16 inches are typically sold as steppers, and may be cheaper than large slabs.
Irregular stones are typically set in sand, or sometimes mortar. They are very forgiving for do-it-yourself installers. Because they are irregular and imperfect, they need not be set at the exact right height or location, and need not even be perfectly level.
If selecting irregular flagstones at a quarry or rock supplier, seek out a wide variety of shapes and sizes so you can fit them together like a puzzle and fill any holes or gaps. Also look for blocks with fairly uniform thickness, between two and three inches thick.
Uniform flagstone tiles are typically set in mortar, and used in more formal patios and projects. They are typically sold by the square foot. Uniform tiles are less forgiving, as they must all be lined up more evenly than irregular shapes.
Flagstone patios are relatively easy to build, but very attractive and durable. However, it’s important to start the job right by choosing the best flagstone from among many available options.
Updated August 6, 2018.
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