By definition, a hydraulic cement is any cement which hardens and sets when chemically reacting with water; this includes Portland cement. In actual use, however, the term is used to refer to cements which expand as they dry and are used to fill cracks and holes in cement structures. The type of cement being referred to is more properly called Calcium sulfoaluminate cement.
The applicable specification standard for hydraulic cement is ASTM C1157 / C1157M – 09 “Standard Performance Specification for Hydraulic Cement”, while the specification for rapid hardening hydraulic cements is ASTM C1600 / C1600M -08.
Calcium sulfoaluminate cements include calcium sulfoaluminate. The calcium reacts with the sulfate to create the special poperties of this formulation, which include expansiveness and quick setting time, typically under 10 minutes, although it will cure to final strength after around 30 days.
So-called hydraulic cement can be used to repair cracks and holes in concrete foundations and walls, swimming pools, ponds, fountains, water storage tanks and masonry joints. It also works well for sealing around metal to concrete joints like pipe or conduit passthroughs, anchor bolts, water pipe form holes and the like.
To patch holes and cracks, begin by cleaning the area to be repaired with a wire brush or abrasives.
Cracks should be chiseled so that the bottom of the crack is wider than the surface, forming an inverted V shape. You can form the inverted V by using an abrasive grinder wheel, preferably silicon carbide, mounted on a power grinder or drill.
Thoroughly flush and wet the area with a sprayer or hose. Mix only enough of the cement to do the job at hand, as it sets up in 3 to 5 minutes.
Then apply it with a trowel or putty knife, forcing it into the crack or void. Smooth it so it is flush with the surface being repaired. A second or third coating can be applied if required.
Tools and surrounding surfaces should be cleaned immediately with soap and water, as once the cement has hardened, it will need to be chiseled off.
Sealing Active Leaks
The fast hardening time means you can even use some brands to stop active leaks in a structure, like a below grade concrete or masonry basement wall. This can be done by mixing the cement into to a putty-like consistency, form it into a conical plug slightly larger than the hole size, and wait until it begins to be hot to the touch.
Then press the plug into the leak hold and hold it there 3 to 5 minutes; it should harden and seal the leak within 15 minutes or so. Of course, this will only be feasible if the water pressure of the leak is low enough for you to stop it with hand pressure.
If the cracks or voids are due to foundation settling or shifting, and the movement is ongoing, then hydraulic cement will only be a temporary cure, as the crack will probably continue to widen.
A few brand names of rapid hardening hydraulic cement which can be used for repairing cement cracks are:
CGM Pro Plug
United Gilsonite Laboratories Drylok Fast Plug
Quikrete Quick-Setting Cement
DAP Quick Plug
There are many more on the market. Just follow the manufacturers instructions on the label.
Hydraulic cement, or calcium sulfoaluminate cement, is alkaline when mixed with water. It can cause irritation or injury to skin or eyes, as can inhalation of dust. Use gloves during mixing and application, and wear a respirator if you have chemical sensitivities. Wash any cement from skin before it hardens.