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Constructing Flagstone Steps in the Landscape

Diana Panhorst


Steps serve many functions in a landscape. One function is to create safe passage and easier movement up and down grades. Steps can also highlight or create garden levels by making outdoor "rooms." Informal steps can be made by using stepping stones placed directly into the ground in a random fashion. More formal steps are constructed with connected straight edges like those found inside a building. Flagstone steps are an example of formal steps.

Varieties of Stone:

Deciding what type of stone to use for your steps will depend on existing colors and materials available in the surrounding area, the style you want to create, the landscape you want to compliment, and your budget. To make an informed decision, it will be helpful to become familiar with some stone terminology. Many different stones are commonly referred to as ‘flagstone' but serve a variety of purposes.

Flagstone: A stone cut to form a shallow, flat slab. They are often used as pavers for patios and paths. They are available in several different thicknesses and can have either a straight edge or a random cut edge. Flagstone is commonly cut from stones that are easily split such as limestone, granite, and sandstone.

Ashlar: A stone that is cut into a straight edged, geometric shape used in building stone walls. Typical ashlar stones are limestone, granite, and sandstone.

Rubble Stone: Any uncut stone that is used for building stone walls and as stepping stones. Rubble stone is usually a hard stone such as basalt, gneiss, or granite.

Fieldstone: Any uncut stone that is indigenous to the area. For example, basalt and granite are typical field stones of Minnesota and Wisconsin.

Belgian Blocks: Paving units with similar dimensions to brick. Belgian blocks are typically cut from granite or other durable stone.

The following table is a list of common stones used in landscaping, their characteristics, and their typical landscape uses.

Characteristics of Stones Used in Garden Features

Rock Texture Color Durability Water Absorption Shapes/Uses
Basalt Fine-grained Grey, black, brown Strong Resistant Usually rubble.
Walls, stepping stones, natural water basins
Gneiss Medium-to coarse-grained Pink-grey, black, white, banded Strong Resistant Usually rubble.
Specimen stones, walls
Granite Fine-to medium-course-grained Pale grey, pink, red Strong Resistant Rubble or ashlar.
Walls, stepping stones, specimen stones
Limestone Varies Grey, black, white, buff Medium-strong to very weak Poor resistance Usually ashlar.
Marble Fine-grained Pink, white, black, yellow, brown Strong Resistant Usually ashlar.
Slabs for walls, paving
Sandstone Varies Buff, brown, blue, black, pink Strong to very weak Somewhat resistant Rubble or ashlar.
Walls, flagstones
Slate Fine-grained Black, green, red Strong Resistant Usually ashlar.

Table from Stonescaping by J.K. Whitner

Stones Native to Minnesota and Wisconsin:

Stones indigenous to the Minnesota-Wisconsin area are: Sandstone, limestone, dolomitic limestone, and granite.

Depending on the location of the quarry, these stones can have different names and different colors. For instance, two popular landscaping stones, Chelton and Fond du Lac, are different types of limestone. They are both from Wisconsin and are sold by the same supplier (Buechel Stone Corp.), but they are found in two different quarries and are different colors. The name of the area or quarry is often the name given to the stone. Granite is an exception. Granite is usually referred to by its shape (cobblers, boulders, rubble, fieldstone).

The following table is a list of Minnesota and Wisconsin stone by type of stone, supplier, name of stone, and color of stone.

Location & Stone Type Stone/Quarry Name Color Supplier
Wisconsin Limestone Lannon Stone Grey, buff, blue, rust, brown, gold Halquist Stone
Wisconsin Limestone Chilton Grey with blue, shades of red and brown Buechel Stone Corporation, Eden Stone Company
Wisconsin Limestone Fond du Lac Beige to white, tan, gold Buechel Stone Corporation
Wisconsin Limestone Eden Grey, white, brown Eden Stone
Wisconsin Limestone Oakfield Tan, cream Eden Stone
Wisconsin Sandstone Highland Brown Antique Reddish-brown Krukowski Stone
Wisconsin Sandstone Sandy Creek White with reddish-brown outline Krukowski Stone
Mankato Dolomitic Limestone Kasota Stone Grey, cream, golden brown Various suppliers
Minnesota and Wisconsin Granite Granite Various colors Various suppliers

Site and Design Considerations:

  • Construct steps if your slope is 33% or more (33% = 1 foot of vertical rise for every 3 feet of horizontal movement).

  • Consider route to stairway, traffic volume, and user's physical capabilities when designing steps.

  • If there is a path leading to the stairs, the stairs should be at least as wide as the path.

  • Stairs in high traffic areas should be at least five feet wide or more.

  • To avoid soil erosion next to steps, install half buried stones (support stones) or a low retaining wall.
Tools, Equipment, and Supplies:

Consider constructing a crude ramp alongside the steps if you are using a wheelbarrow or heavy equipment. The ramp will allow you to move equipment and supplies more easily.

  • Straight long wooden board
  • Measuring tape
  • Chalk or pencil
  • Carpenter's level
  • Wheelbarrow
  • Mortar (4 parts concrete sand to 1 part Portland cement)
  • Mortar pan
  • Trowel
  • Crushed rock (Class 2 or 5)
  • Hand tamper
  • Shovels
  • Eye protection
  • Stonemason's chisel or a brickset
  • Club hammer
  • 2" thick Flagstones of desired size *
  • Granite Belgian Block riser stones **
  • Granite Belgian Block support stones -- approximately brick size ***
* The size of the flagstones should be the desired length of the tread, plus the thickness of the riser, plus 1 inch for overhang. For example, a 15-inch tread with 4-inch riser blocks will need flagstones that are 20 inches in length. The tread can also be composed of a couple of flagstones to make up the 20-inch length (see Preparing Flagstone below).

** The height of the riser stones are 2 inches less than the height of the total riser (the flagstone will make up the other 2 inches). The thickness of the block should equal its' height. For example, a 6-inch riser will need a 4" x 4" granite belgian block.

Diagram 0

*** You will need two support stones for every step including the base step. The support stones will prevent soil erosion next to the steps.

Preparing the Flagstone:

Select stones that will properly fit the dimensions of the tread. Frequently, stones that will not fit the tread dimensions will require cutting.

  • Align the stones together in a space equal to the needed dimension (tread length and tread width - including 1 inch overhang, plus the width of the risers).

  • Mark with chalk or pencil any pieces that do not fit. Mark the line to be cut on both sides of the stone.

  • Use a chisel to score 1/8-inch grooves into the slab on both sides.

  • Use a club hammer to gently hit along the cut line on either side of the slab. The stone should split along the scored line.
Mixing Concrete:

A general-purpose concrete mix that works well for this type of project contains:

1 part Portland cement
3 parts concrete sand
2 parts coarse aggregate (3/4 inch particles)
0.5 parts water (this is approximate and depends upon the moisture content of the sand)
Use a ready mix concrete
A ready mix concrete may be the most convenient to use because only a small amount of concrete is needed for the base. In cold climates, where freeze-thaw causes significant soil movement, it is advisable to use a ready mix that contains an air entrained admixture. A local supplier can advise you on the proper ratio of admixture to cement mix. Less water is needed when using an admixture.

The amount of water added to a cement mix is critical for obtaining the desired consistency. To obtain the desired consistency, add water slowly and periodically perform a "squeeze test". To perform a squeeze test, take two handfuls of cement mix into one palm and squeeze it. The water content is correct if the concrete does not crumble (too dry), or ooze through your fingers (too wet).

To mix the concrete:

  1. Add the cement to coarse and fine aggregates.
  2. Mix ingredients with a shovel by adding the material at the edge of the pile to the middle and folding it over.
  3. Form a crater in the middle of the pile and add most of the water
  4. Mix as in step 2.
  5. Add additional water in small increments using a watering can until desired consistency is obtained.
Mixing Mortar:

Mortar differs from concrete in that it contains sand and cement, but not heavy aggregates. Mortar may contain additives, such as lime or plasticizer, which improves its flexibility.

To make a mortar mix, combine:

1 part Portland cement
4 parts concrete sand
1 part masonry cement
3 parts concrete sand
The procedure used for mixing cement can also be used for mixing mortar. Water is again the critical factor. The mortar mix is at the right consistency if a blob of mortar sticks to a piece of metal that has been turned upside-down.

Concrete and mortar have a limited amount of time before they become unworkable. It is recommended that a batch of concrete or mortar be used within two hours.

Step-by-Step Process for Constructing Flagstone Steps:

I. Determining the Slope

The height of the slope governs the tread/riser ratio and the number of steps that will need to be constructed. The slope equals the rise divided by the run. The rise is the height difference from the top of the hill to the bottom. The run is the length of the slope.

An easy way to determine the slope (vertical drop) is to use a straight wooden board or pole, a tape measure, and a carpenter's level. As shown in the diagrams below, the board is laid level, horizontally at the top of the slope, using the carpenter's level. Next, using the tape measure, measure the height of the board at the bottom of the slope. The measurement is the height of the slope.

Measuring the rise
Measuring the rise

To measure the run of the slope, stand the board upright at the bottom of the slope, making sure the board is level. Measure the distance from the top of the slope to the board. The measurement is the length, or run, of the slope.

Measuring the run
Measuring the run

II. Calculating the Tread/Riser Ratio

For outside steps the height of each riser should be a minimum of 4 inches and a maximum of 6.5 inches. A 15-inch tread and a 6-inch riser is a comfortable tread/riser ratio recommended by most landscape architects.

You can choose either the tread or the riser dimensions first, depending on the style of the steps you plan to build, and its users. To calculate the tread/riser ratio use the equation:

tread + 2x riser = 26 to 27 inches
or use the chart below.

Typical tread and riser dimensions for outdoor steps

Tread (inches) Riser (inches)
19 4
18 4.5
17 5
16 5.5
15 6
14 6.5
13 7

The tread and riser dimensions should be the same for each step in a set of stairs. Changing the dimensions of individual steps will cause visitors to trip.

When choosing a tread/riser ratio, consider the rise and run of your slope, but do not try to make the ratio fit your slope. Doing so can cause a poor tread to riser relationship. In most cases, it will be necessary to either dig into, or fill in the slope, or possibly both in order to create a comfortable flight of steps.

III. Shaping the Slope for Steps

Excavate the rough shape and dimensions of the steps.

IV. Preparing the Base Step Foundation

A flagstone is placed level with the adjacent ground. This is the base tread that anchors the flight of steps and acts as the foundation.

  1. Mark out the base tread at the bottom of the steps.

  2. Excavate to a depth of 12 inches.

  3. Place 4 inches of crushed rock (class 2 or 5) in excavated site. Tamp firmly.

  4. Pour 4 inches of concrete over compacted rock. Allow concrete to cure (dry) for a minimum of 24 hours before laying stone.

  5. Excavate several inches on each side of the step to a depth of 2-3 inches.

  6. Place a support stone on angle at each corner and on each side of the step.

    Detail of first tread construction
    Detail of first tread construction (adapted from Stonescaping by J.K. Whitner)

  7. Apply a 2-inch thick layer of mortar on top of the concrete foundation. Spread the mortar out to the sides to set the support stones.

  8. Press the flagstones into the mortar making sure that the flagstones are level with the adjacent surface. Wipe away excess mortar.

  9. Level the flagstones using the carpenter's level.

  10. Mortar between flagstones. Wipe away excess mortar. Allow mortar to cure for three days.
V. Constructing the First Riser
  1. Apply a 1-inch thick layer of mortar to the back of the base tread. The width of the mortar layer should be equal to that of the riser stone.

  2. Press the riser stones into the mortar.

  3. Add tamped soil or rubble as backfill between the riser stones and the earth's foundation.

  4. Mortar the riser stones together. Wipe away excess mortar.

  5. Level the riser stones using the carpenter's level.

  6. Allow mortar to set.
VI. Installing the Steps
  1. After the mortar on the first riser has set, excavate the tread area behind it to a depth of 6 inches.

  2. Add 3 inches of crushed rock. Tamp firmly. Add enough crushed rock so that after it is firmly tamped, it is 2 inches below the top of the preceding riser.

  3. Apply 2 inches of mortar over the crushed rock.

  4. Lay the flagstone treads on the mortar so that there is 1 inch overhanging the riser.

  5. Level the flagstones using the carpenter's level.

  6. Mortar between the flagstone treads. Wipe away excess mortar.
image (adapted from Stonescaping by J.K. Whitner)

Repeat procedures V and VI until all treads and risers have been completed. Allow the steps two weeks to fully cure before using them.

Mortared flagstone steps
Mortared flagstone steps (adapted from Stonescaping by J.K. Whitner)


Fitzgerrell, S. 1991. Sunset Basic Masonry. Sunset Publishing Corporation. Menlo Park, CA.

Garden Projects. 1985. Arco Publishing. New York.

Hedberg Aggregates. Supplier of aggregate and stone. Plymouth, MN.

Putman, R. 1988. Modern Masonry. Harcourt Brace Jovanovich Publishers. Orlando, FL.

Whiteley, P. 1991. Sunset Garden and Patio Building Book. Sunset Publishing Company. Menlo Park, CA.

Whitner, J. 1995. Stonescaping. Garden Way Publishing. Vermont.

Wirth, T. 1984. The Victory Garden Landscape Guide. Little Brown and Company. Boston.

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