Mortar, which is comprised of a mixture of concrete, sand, and added water, is used for a sealant between stones, and also to create a bed into which stones can be imbedded. Though it is not as strong as concrete, its makeup allows for a little more flexibility of use. Mortar can be used to set the stonework around the edges of ponds, in waterfall fixtures, and within the beds of man-made streams. It can be purchased in premixed 80-pound bags, but if you’re involved with a project that involves using a large quantity of it, you might consider mixing your own.
The standard mortar mix contains 1 part lime, 2 parts cement and 9 parts sharp sand. Wheelbarrows have been the time-honored containers for mixing these ingredients because of their size and mobility. Begin by mixing the dry ingredients thoroughly with a shovel or hoe. Add water a little bit at a time and continue to mix, examining the consistency as you proceed. Mortar that is too thick won't bond well; but if it is too thin, it will run off without adhering. It's helpful to have some quantities of the dry mix set aside. If the mix ends up too runny, adding more cement and sand can amend it. Well-mixed mortar can be shaped into small peaks, like towers, that will hold their form. Another remedy for a runny mix is to allow it to settle for half an hour. Excess water will rise to the surface and can then be skimmed off.
Mortar is usually applied in one-inch-thick layers. When stones are set in place, this will squeeze out some of the mortar, which can then be spread with a trowel. You can also apply it to crevices within existing stonework, smearing it with the trowel and then cleaning up the excess. Wire brushes are helpful for scrubbing rock surfaces to remove crumbs of mortar and restore their natural appearances.
Curing mortar is a process whereby its chemical action takes place over a course of days and results in a hardening of the surface. It should be kept moist for the duration of this process, which can take up to six days. Cover mortared areas with sheets of plastic or wet burlap. Once it has set enough so that it can't be washed away, it should be wet with hose water a couple of times a day, especially in hot weather. Heat can make mortar dry too quickly before it becomes sufficiently hardened and cohesive. Extreme cold can also weaken the mixture by disintegrating it before it has cured.
Mortar can even be a building tool all of its own. Gunnite, which is used to form imitation rock creations - for example, the bed of a stream - is essentially mortar that is blown through a special gun. This approach can be much cheaper for large landscaping projects that otherwise would require the shipping and setting of massive amounts of stone.