If the hole takes grout very rapidly, use of a thicker mix can be warranted, except in the special case where large voids are present; the water test before grouting should have indicated whether such voids are present.

Usually, a fast take with minimal pressure buildup indicates that the cracks will probably accept a thicker mix without blocking. Therefore the grout should be thickened by one step (the steps are detailed below) and injected into the hole so as to use the thickest practicable grout and thereby gain maximum durability.

Further thickening of the mix might be warranted if grout behaviour warrants this.

STANDARD MIXES and THICKENING STEPS

There is no need to use any other mixes than

•       5 : 1 by volume
•       4 : 1
•       3 : 1
•       2 : 1
•       1 : 1
•   0.8 : 1
•   0.6 : 1
•   0.5 : 1

These mixes give adequate increments in viscosity. Mixes in between give negligible extra control over viscosity and are only a nuisance.

When thickening the mix during grouting, proceed down the list one mix at a time - never jump a mix. For instance, if thickening from 3 : 1, go to 2 : 1 for a while and then to 1 : 1 and perhaps on.

Never go straight from 3 : 1 down to 1 : 1 or else the too sudden thickening is liable to prematurely block cracks in the job.