To grout flagstone, remove cracked or loose mortar from the flagstone using a chisel, then sweep the bedding floor to remove loose stones and debris. Fill a grout bag with sand and Portland cement mortar mix, then squeeze it from the nozzle into the gaps between the flagstones to fill them completely. Lastly, press the joints using a jointer tool, then wipe the face of the flagstones with a sponge.
Flagstone refers to any flat, split stone and may be made of limestone, granite or sandstone. The product is used to provide a rustic, natural feel when used to construct garden walkways, patios and even floors within the home. Grout is used to hold the flagstone firmly in place and prevents debris from collecting between the stones.
Adding hydrated lime to the mortar mix improves the plasticity and workability of the mix, making it easy to squeeze it through the grout bag nozzle. Lime also makes the water more waterproof and reduces shrinkage and cracking during the curing process. To get optimum results, replace 10 to 15 percent of the total volume of sand with hydrated lime.
Grouting flagstone should ideally be done in cool to slightly warm weather. The flagstone should be covered with waterproof insulating blankets for at least 48 hours, according to AskTheBuilder.com.