It is important to note that colder temperatures will require extended cure times. A good rule of thumb to follow is that for every 18 degrees Fahrenheit (10 degrees Celsius) below 70 degrees Fahrenheit (21 degrees Celsius), the installation should cure for twice as long in order to reach the desired result.

Critical detailing and expansion joints

Proper detailing also needs to occur when the stone paving transitions to other areas and when changes occur from one surface finish type or plane to another.

Possibly the most important detail to include when designing and constructing an exterior paver application are the expansion joints. Due to the demanding nature of these projects, exterior installations will require more frequent and wider expansion joint placement.

For example, the North American Tile Council (TCNA) suggests that exterior expansion joints be placed every 8 feet (2.8 meters) to 12 feet (4 meters) in each direction (Detail EJ-171). Typically, joints placed 8 feet (2.8 meters) on center should be no less than 3/8 inch (9 mm) in width, and joints placed 12 feet (4 meters) on center should be placed no less than ½ inch (12 mm) in width.

However, notice that minimum widths should be increased 1/16 inch (1.5 mm) for each 15 degrees Fahrenheit (5 degrees Celsius) stone surface temperature change greater than 100 degrees Fahrenheit (36 degrees Celsius) between summer high and winter low. (Decks exposed to the sky in the Northern U.S. usually require ¾-inch-wide (19 mm) joints on 12 feet [4 meters] centers).

Typically, a dark stone paver can reach temperatures of 140 degrees Fahrenheit (58 degrees Celsius) in the summertime and then experience -10 degrees Fahrenheit (-21 degrees Celsius) in the dead of winter. That calculates to an additional 3/16-inch (4.5 mm) increase in width.

It is important to note that these types of applications will require calculated expansion joints that are determined by the project engineers rather than following industry-provided “guidelines.” Factors that are important to the equation include the coefficient of expansion rate for the concrete substrate, the mortar bed, the stone being used and the temperature extremes that each unique project will experience.

Samplings of these rates per degree Centigrade are as follows:

Portland cement concrete - Sandstone

0.9 to 1.2 x 10-5

Granite

.0000085

Marble

.0000110

Typical latex Portland cement mortars

.0000065

Brick

.0000055

Steel (drains, curbs, etc.)

.0000120

When all of these rates are factored, the appropriate amount and width of movement joints can be calculated.

The project architect or engineer should provide direction on the design, placement and construction of all expansion joints. The movement joints should be fully functional and be brought up through the setting bed and stone layer from where they are placed in the substrate. Many times, additional movement joints are required even if they do not occur in the substrate. The setting bed and finish layer should still accommodate any movement that may occur. The sealant chosen for these joints should also be durable, weather-resistant and be able to handle the movement that it is subjected to. Typically, silicones and urethane sealants are best for these applications. Latex or acrylic caulks are only suitable for interior non-wet areas. Most of the sealants produced match the grout or stone colors to blend in with the entire color scheme of the installation.

Generally, latex-fortified Portland cement-based grouts are used for exterior paving projects.

The stone being used for the application should also be carefully chosen. Some types of stones may not be suitable for exterior paving, vehicular traffic or exposure to moisture. Make sure that the stone manufacturer or supplier of the stone recommends their stone for your specific application. When all of these factors are taken into consideration, a beautiful and successful exterior stone paver installation will be achieved.