how to: mix mortar

Mortar can be useful in pond building. if mixed and applied correctly, it has superior adhesion when compared to waterfall foam and is less costly. It also allows for leveling and raising stone etc. and when bed onto liner, it keeps stone in place and the water from disappearing in the stone

About Mortar

As it pertains to ponds, mortar is great for bonding stones in waterfalls, leveling stone, and to direct and contain water. It is important to realize neither mortar or concrete are inheritably waterproof. To create a waterproof structure there are several options

For one, a liner should be placed underneath the stone. I have seen a number of leaking concrete ponds & waterfalls without a liner placed underneath. Waterproofing powders/mixes can also be added to the mortar mix to create a water tight seal. Liquid rubber or fiberglas can also be painted on a cured concrete thereby rendering it watertight

The big key with mortar or concretes that it should be allowed to cure slowly so that the chemical reaction is properly completed. If the mortar does not cure properly it will not have any strength. To slow the drying process, the mortar should be sprayed down with water several times a day in order to keep it moist. In excessively hot weather it should be covered with burlap to stop it from drying out rapidly. Also make sure not to add too much water creating a sloppy mix as this lessens its strength
  • Portland cement, Masonry Cement and sand are the main constituents of mortar
  • It is easier to dry mix the constituents before adding water
  • An acrylic based liquid bonding agent can be added which aids flexibility and strength
  • The mix should be thorough and stiff. If you add too much water, you end up with a weaker finished product

You can buy ready mix mortar in a bag or mix the constituents on your own. I prefer to mix my own. When you mix your own, you can control the ratios. For example I prefer a mixing ratio of 1:0.5:3 - 1 part portland, 1/2 part masonry and 3 parts sand. Type S cements are stronger than type N and should be chosen. Soft sand is also desired over gritty sand when doing stone work. Masonry cement provides a strong bond as well as being able to deal with freezing and thawing. Portland cement supplies flexural strength and adhesion

When applying mortar to rocks, it is a good idea to prep them with a wire brush. This is easily accomplished with a cordless drill. This cleans any dirt and loose debris away. You should also wet the stone or even apply a slurry mixture made of portland cement and bonding agent

When stacking the stones, pack the mortar in as best as possible and be aware of aesthetics. It is usually not advisable to stack more than 3 stones [2 layers of mortar between the 3 layers] before letting the mortar cure - stability or placement will likely be an issue if you do. The use of shim stones also helps maintain postponing, and a level is required to ensure a forward slant and left to right placement. Of course waterfall foam is a good alternative to mortar and it is particularly advantageous when trying to get a quick seal and bond between liner and stone