The suggestions offered herein are intended as an aid to help the operator identify some of the factors that need to be taken into consideration when mixing and pumping cementitious grouts. Because a wide variety of materials are available for many different applications, it is incumbent upon the operator to become familiar with the specific characteristics of the material he intends to use.
Among the commercially manufactured materials available in todays market are materials for structural repairs, floor toppings, high strength non-shrink grouts, manhole and sewer lining mortars and other specialty materials. Each of these materials has unique characteristics, which must be well understood to insure a successful application.
In general, most materials need to be of a flowable or pourable consistency for successful pumping. This means that if the material can be poured out of a pail or bucket, it can likely be pumped. The exception to this requirement is repair mortars, which tend to be mixed in a thicker consistency and require special pumping techniques. Materials that contain aggregates pump best and perform best when the consistency is kept to the lower range of pourable; that is, not too wet.
Some materials contain accelerating admixtures to reduce the setting time. This is particularly true of repair mortars and other spray applied materials so that strength gain can be fairly rapid. It is important to keep moving when using these types of materials. Once the material is mixed, it must be pumped immediately and kept in motion and subsequent batches must be mixed and pumped as rapidly as possible. Any delays in the application process could result in plugged hoses and equipment. Temperature also has an effect upon these materials to the extent that exposure of the hose to the sun on a hot day will accelerate the set time even more; therefore this should be avoided. It may even be necessary in some cases to cool the material, the mix water, or even the hose itself.
Pumping distances should always be kept to a minimum, and hoses should run as straight as possible no matter what material is being used. Sometimes circumstances require longer than usual hose lengths; when this occurs, every effort should be made to use every advantage possible to insure a successful application. Some materials simply cannot be pumped for long distances, so its best to know the proposed material characteristics before attempting a production procedure.
Before attempting to mix and pump production materials, it is prudent to rinse the mixer and charge the pump hopper with sufficient water to thoroughly flush the pump and all grout lines. This is to purge the grouting system of any residual materials or scale that may exist. Once that is completed, remove the grout hose from the pump and drain out all water by elevating one end, or by progressively elevating the entire hose, starting at one end and proceeding to the other.
Next, mix a slurry composed of portland cement in approximate proportions of 6-1/2 to 7-1/2 gallons of water to one bag (94 lbs.) of cement, and pump this through the grouting system. This is to remove any residual water from the hose, lubricating it for the production material to follow. Now the production grout may be mixed and pumped immediately behind the slurry mix, which is thus evacuated from the hose, and may be retrieved in a bucket. Do not attempt to pump production material through a dry hose.
Finally, one last word about procedures. Occasionally, no matter how conscientious an operator may be, a hose will get plugged. Once this happens, the only sure way to remove the plug is to empty it of material. Beating on it with a hammer or running over it with a vehicle will not usually be successful. A prudent operator will be prepared for such eventuality by having readily available a sufficient length of small diameter stiff tubing, hose or plastic pipe to which he can rapidly connect a water source and flush the grout from the hose.