Installing flagstone over a wooden deck is not a complex task, but there are a couple key aspects of the project to keep in mind. The wooden deck must be structurally sound before any flagstones can be installed. This may involve replacing or reinforcing some of the structural supports of the deck. Once the structure is solid, the surface of the deck must be covered with a cement backer board. Once the backer board is installed, the flagstones can be set and grouted.
Preparing the Surface
Once the deck is structurally sound, the surface should be covered with quarter-inch backer board. The backer board is a cementlike material that comes in 3 by 5 feet sections. This material, which prevents the flagstones from shifting and cracking, can be screwed down to the wooden deck with masonry screws.
Laying the Flagstones
Flagstones can be applied in a desired pattern with thinset adhesive. Most flagstones are irregularly shaped, so the spacing between the stones isn't precise, but a matter of personal preference. The adhesive must set for 24 hours before applying grout in the gaps between stones. Grout must set for 24 hours, too.