Frequently Asked Questions

Why is it critical to control the water addition very precisely when mixing Conbextra BB72IN?

The water-to-powder ratio is the single most important variable in determining the strength and shrinkage properties of a cementitious precision grout like Conbextra BB72IN. Adding more water than specified increases fluidity (making placing easier) but significantly reduces the 28-day compressive strength and changes the expansion/shrinkage characteristics, potentially causing net shrinkage and loss of base plate contact. Adding too little water makes the grout too stiff to flow and fill the void beneath the base plate. The product data sheet specifies a narrow range of water addition by weight per bag — this must be measured with a graduated container and not estimated. A consistent mix can only be achieved by measuring the water volume for every batch.

How long after grouting can machinery be started or load applied?

The timing for loading the base plate after grouting depends on the compressive strength development of the Conbextra BB72IN grout and the minimum strength required for the specific loading. In hot Indian conditions (above 25 degrees C), the grout typically achieves 20 to 30 MPa within 24 hours and above 40 MPa within 3 days. In cooler conditions (below 15 degrees C), strength gain is slower. The minimum strength required before loading is determined by the equipment supplier and the structural engineer — typically 20 to 25 MPa for most machinery bases. Always test the actual compressive strength by keeping cube samples cured in the same temperature conditions as the base plate grout before authorising loading.

How should the base plate and foundation be prepared before grouting with Conbextra BB72IN?

Proper surface preparation is essential for achieving full contact and maximum load transfer through the grouted base plate. The concrete foundation surface must be free of all oil, grease, laitance, loose aggregate, and contamination — mechanical preparation by scabbling, grinding, or hydroblasting to expose clean, sound concrete aggregate is required. The prepared surface must be thoroughly pre-wetted to saturated surface dry condition immediately before grouting (no standing water). The base plate must be set to the correct level and alignment using levelling bolts, wedges, or shims, with adequate space (minimum 25 mm) for the grout to flow under the full area. Vents should be provided at the highest point to allow air escape during grouting. After the grout has set and cured to the required strength, all levelling devices should be removed or cut flush, and the void left by the levelling devices should be filled with fresh grout.