Q: We have a flagstone patio with the stones mortared in place. But the mortar is crumbling away, leaving the stones loose, making a couple of steps particularly dangerous. To repair this, do I need to remove the stones and start all over? And what sort of mortar should I use?
A: Stone patios are often built on a flexible base of crushed rock and sand to avoid the problem of deteriorating mortar. But with features such as steps, a rigid, mortared base is the only way to build. The problem is that the water in the mortar mix causes the concrete to shrink as it cures. Particularly in colder climates up north, the freeze/thaw cycles will cause the concrete to expand, which creates voids between the pavers and eventually leads to crumbling mortar. To fix this, first use a hammer and small chisel and chip away the old, loose mortar. Sweep the joints clean. Next, mix a batch of mortar consisting of three parts Portland cement and five parts sand. Use only enough water to make a semi dry mix; it should not slosh around like regular cement. Trowel the mortar between the pavers and tamp down the pavers and mortar using a mallet and blocks of wood. [Non-text portions of this message have been removed]
