Can I Lay Slate on Top of a Concrete Porch?

Slab Basics

• While a concrete slab does not need to be level for a slate tile installation, it does need to be flat. If there are hills and valleys in your concrete porch floor you will need to flatten them out with a concrete-based mixture prior to installing the slate. Thinset mortar can be used to fill in the valleys for sloped slabs, while level floors can be filled in with a self-leveling compound.

Indoor Slab

• Indoor slabs can have slate material installed directly on top of the slab with little regard to anything other than the flatness of the floor, although if there are expansion joints you will need to take those into consideration. Expansion joints are cut joints that run through concrete slabs and tile installations to allow for seasonal movement of the concrete material. Any slab expansion joints need to be mirrored in the slate installation, with a joint in the slate tile installation placed directly on top of the slab expansion joint. It must be filled with caulk rather than normal grout to allow for expansion and contraction of the slab due to the climate.

Outdoor Slab

• Preparation for outdoor slabs is the same as for indoor slabs, except you may also want to protect the slate with a layer of sealer afterward if you live in an area where there is a freeze/thaw cycle. Concrete and slate tile are both porous and can breathe, thus shedding moisture naturally. Adding a topical coat of sealer to the slate can help protect it from excessive moisture during snow melt, which can help the tile survive expanding water during freeze cycles.

Weather

• The climate and weather affect whether or not you can install slate tile on top of a concrete porch in an exterior setting. If the slab is prone to holding moisture from damp soil, you will not be able to install slate tile because of the inherent mold and mildew issues. If the slab is simply wet from rain, on the other hand, you just need to wait for it to dry before installing the slate.