Ground heave solutions

The ideal moment depends on the concrete mix and pour depth. The general rule? Irrigation should begin once the concrete reaches self-supporting strength. When the slab is securely held by piles and beams, Clayboard has fulfilled its role perfectly as part of a reliable ground heave solution.

A useful rule of thumb: one Voidpak per 24m². For buildings with internal beams that divide the footprint, ensure at least one Voidpak per enclosed area of Clayboard, adding more if the area exceeds 24m².

Yes, it does. When using Clayboard in lay-flat tubing sections, stick to three panels per section for easier handling. In this setup, one Voidpak pipe is needed per bagged section, instead of the usual one per 24m².

Absolutely! While intact, Clayboard keeps the insulation securely in place. If the ground dries out and shrinks, extra support may be needed. Attach wire ties to mesh or rebar, or anchor the insulation with wide helix plastic screws into the concrete during the pour. These steps help ensure that your ground heave solutions remain effective and maintain their integrity over time.

Not at all. The Voidpak pipe isn’t for removing Clayboard but for softening its honeycomb core. Water reduces its compressive strength from 30kN/m² to a gentle 2-3kN/m², allowing the Clayboard to yield easily when the ground heaves. It’s much more forgiving than polystyrene void formers, which require precise load calculations.

Yes, but you must keep an eye on the weather. Since Clayboard collapses when wet under pressure, it must stay dry while supporting steel and wet concrete. This is crucial for effective ground heave solutions. Clear any standing water before laying, and in trenches, consider a sump and pump to manage pooling. Pea gravel might be a better choice than sand, as wet sand can retain water longer. And try to minimise the time between laying Clayboard and pouring concrete. Proper handling ensures that your ground heave solution remains effective even in challenging conditions.

Not a problem. Sand blinding provides a smooth, flat surface that prevents point loadings on Clayboard and aids water drainage. After irrigation, a steel rod can be used to break through the bottom skin via the Voidpak pipe opening to let excess water drain. With concrete blinding, just give it an extra tap to ensure water can escape.

The correct thickness is typically based on soil analysis at the site. NHBC guidance relies on the Modified Plasticity Index (PI), which measures the difference between the soil’s liquid and plastic limits. In simpler terms, a lower PI percentage indicates less volume change. Clayboard thickness is determined by the void depth plus 10mm. Being slimmer than polystyrene void formers, Clayboard also reduces excavation and muck away, saving on costs and time. Choosing the right thickness ensures your ground heave solution is both efficient and effective.

Not at all. Clayboard is designed for use under suspended slabs, not ground-bearing ones. The slab is supported by beams, so even when Clayboard loses its strength, there’s no risk of slumping. In cases with a piled raft, other building elements take over the load, keeping everything rock solid.