·        Cementitious grouts

These grouts use high water-cement ratio, although in some cases powdered plasticisers are added to reduce water demand. Such grouts, due to the high water-cement ratio end up as mere void-filling materials and are generally useful in providing temporary solutions. The shrinkage loss of water is a cause of worry too. However, where cost is a major constraint and special structural or any other requirements are not playing a major role, this type of grouting is generally adopted. The shrinkage problem in this grout can be overcome with the use of shrinkage compensating cements.


·        Expansive cementitious grouts (Non-shrink grout)

This is a modified cementitious grout in which the shrinkage effect is controlled by incorporating either gas producing agents or chemicals like lime or calcium sulpho aluminate which cause expansion in the mass. The grouts produced from calcium sulpho aluminate give good service and performance than those produced from gas producing agents, which are not so effective in terms of contact, good adhesion, desired high elastic modulus, chemical resistance and protection against corrosion. This is because the expansion produced due to hydrated calcium sulpho aluminate is more uniform, stable, controllable and is available even in the hardened state. In the latter case, the dispersion of metallic powder in cement is usually not uniform and while the expansion is not steady the same is available only during the plastic stage. Moreover, there is a possibility of corrosion of reinforcement due to the generation of hydrogen gas.


·        Inorganic liquid grouts

In many cases cementitious grouts do not offer sizeable relief because these grouts being insoluble powders do not disperse uniformly in water and do not reach the various capillaries properly. The reach of a single grout is not substantial, thus many grouts are needed to cover the entire periphery of a structure. In the chemical grouting method a clear solution of a silicate-based chemical A is injected first which reaches easily to all the capillaries being a watery liquid and also spreads in the larger areas without any discontinuities. Almost immediately afterwards, a solution of a precipitating agent chemical B is injected which also spreads similarly. On coming in contact with chemical A, an insoluble precipitation is immediately formed. Wherever these two materials meet, including at the extreme ends of the capillary networks, voids and pores are filled blocking the entire passage. Such a method is particularly useful in arresting dampness in foundations and costs much less than other polymeric grouting. These can totally discontinue the capillaries and hence effectively bring down dampness of the structure. Several alternatives can be suggested for such methods. However, care is to be taken that none of the resultant products is a soluble sulphate, chloride or any other radical which will affect the concrete or steel.


·        Low viscosity epoxies and polyurethanes

These are polymer grouts consisting of two or three-pack system in which one part is necessarily a resin and others are accelerators / curing agents. Once the curing agent is added to the resin, setting process or cross linking process starts irreversibly with visual increase in viscosity as the time passes. Often, this creates problems in the grouting performance by adhering to any obstacle in the passage as a result of increasing viscosity. At such times, the remaining part of the passage / capillary may never get filled. Hence the very purpose of grouting gets defeated. This also creates problems in the cleaning operation of the pressure device.

Sometimes, these grouting materials are modified by diluents to lower the viscosity of the grout or the amount of curing agent is adjusted so as to increase the setting time. In such cases, the strength parameters of the matrix are found to suffer. However, for fast-setting and underwater setting wherein faster strength developments are required, epoxy and PU systems are very useful. Polyester resins are also used for grouts in some parts of the world. These systems are quite costly because the resins themselves are costly and these are generally to be grouted in the pure resin form and a filler material cannot be added into the system which could have reduced the cost of the system. The mechanical injection pressure systems developed for this are costly too, since high pressure producing pumps are required due to high viscosity of the materials.


Generally, these systems give good adhesion to dry surface but do not behave well in wet conditions. Such systems are not quite desirable since they are fire hazardous. In fact, PU systems may create obnoxious gases like isocynates under combustible conditions. Still, these systems were quite popular due to the dearth of better and more suitable materials. However, water-based polymer systems are now available and can be mixed with cement. These co-matrices offer better convenience and superior cumulative performance as compared to other contemporary materials.