Frequently Asked Questions

What is the minimum gap height under a machine base plate that Conbextra HF can flow into and how does its flow compare to Conbextra GP2?

Conbextra HF is specifically designed for grouting narrow gaps that are difficult or impossible to fill with standard-flowability precision grouts like Conbextra GP2. The minimum gap height that Conbextra HF can fill depends on the distance the grout must travel and whether the gap has a smooth or rough lower surface, but as a general guideline, Conbextra HF can fill gaps as narrow as 10 to 15 mm height over short distances (up to 300 to 500 mm horizontal run) and gaps of 15 to 25 mm height over longer distances (up to 1,000 to 1,500 mm horizontal run from the entry point). Conbextra GP2 at standard grout consistency (targeted at 250 to 300 mm flow table diameter) requires a minimum gap height of approximately 25 to 50 mm for adequate flow under a base plate. For a large machine base plate (say, 2,000 mm by 1,500 mm) where the gap is 30 mm and the grout must fill from one side to the other (1,500 mm flow distance), Conbextra GP2 at standard consistency may stall and not reach the full extent of the plate — particularly at the corners. Conbextra HF at 400 to 600 mm flow table diameter can fill this plate at 30 mm gap height comfortably. For very narrow gaps (10 to 15 mm), the maximum practical flow distance with Conbextra HF is shorter — the frictional resistance of the narrow gap absorbs the flow energy and slows the grout before it reaches distant areas. For very narrow, long gaps, Conbextra HF may need to be pressure-assisted (a simple sealant-gun or grout pump pressure applied at the entry point) to drive the flow to the far end.

How is Conbextra HF mixed and placed under a large base plate with a restricted grouting access — for example, a turbine base where only one grouting pocket entry is available?

Grouting a turbine or large compressor base plate with a single grout pocket entry point using Conbextra HF requires systematic planning of the grout flow to ensure complete void filling under the entire base plate from the single entry point. The procedure is as follows. Before placement, the base plate should be levelled and shimmed to the precise bearing level, and the perimeter of the base plate should be sealed with formwork boards on three sides to prevent grout flowing out at the edges prematurely — leave the entry side open for grout pouring. The single entry pocket should have the largest practical cross-sectional area to minimise entry resistance and allow rapid grout flow. Mix Conbextra HF in a clean drum by adding the measured quantity of water (strictly within the specified range — over-watering reduces both strength and non-shrink performance) to the drum and then pouring in the dry powder while mixing with a slow-speed drill and paddle mixer at 400 to 500 rpm until a smooth, lump-free grout is achieved (typically 3 to 4 minutes of mixing). Do not mix individual bags individually for large pours — batch-mix several bags with consistent water per batch to maintain uniform consistency. Pour the mixed Conbextra HF continuously into the entry pocket from a constant height (a raised container or hopper creates head pressure that drives flow under the plate) and monitor the opposite edge through a small vent or inspection point for grout breakthrough. The key to successfully grouting a large base plate from a single entry is continuous pouring without stopping — pausing allows the leading edge of grout already under the plate to begin stiffening, which prevents subsequent grout from flowing past it. Once grout breakthrough is observed at the opposite edge or at all perimeter edges, filling is complete. Allow the grout to reach initial set before removing perimeter formwork (typically 2 to 4 hours).

Can Conbextra HF be used for horizontal construction joints where concrete is poured over a previously cast foundation slab and is it suitable as a structural connection grout?

Yes — Conbextra HF is suitable for use as a structural connection grout at horizontal construction joints where concrete or grout is placed on a previously cast and cured concrete foundation, provided the substrate preparation is adequate and the grout thickness is within the practical placement range. For typical structural base plate grouting (10 to 75 mm grout layer between foundation concrete and base plate), Conbextra HF provides more than adequate structural performance: at 55 to 65 MPa compressive strength, the grout is typically stronger than the underlying foundation concrete (typically M25 to M35 grade in industrial construction), meaning that the connection capacity is governed by the concrete strength rather than the grout strength. For horizontal construction joints between two pours of concrete in a multi-stage pour sequence — for example, a pump base pedestal where the lower section is cast and the upper section is formed and cast later — Conbextra HF can be used as the bridging grout to fill the gap between the two concrete sections and create a continuous structural connection. In this application, the key requirements are: the previously cast concrete must be prepared (roughened by chipping, grinding, or hydro-jetting to a minimum aggregate exposure profile) and the laitance removed; the previously cast concrete must be at SSD condition when the Conbextra HF is placed; Nitobond EP epoxy bonding agent should be applied to the prepared substrate and the Conbextra HF placed wet-on-wet for maximum interfacial bond strength; and the gap height must be sufficient for the Conbextra HF formulation (minimum approximately 10 to 20 mm gap height for effective placement and consolidation under gravity flow). Pull-off adhesion testing of the grout-to-substrate interface should be specified for critical structural connections to verify the bond meets the minimum required by the structural design.