Self-Build Project, School Lane, Rowberrow, Somerset  

Background

Located in the hamlet of Rowberrow in the Mendip Hills, this self-build project involved the construction of a two-storey house by Architect Simon Corbett. The intention was to build a two-storey house on a site where the existing property had been demolished. However, because the location was in an area of outstanding natural beauty, the skyline had to be preserved and could not exceed the height of an adjacent bungalow. Therefore, planning permission could only be given for a single storey above ground level. The solution was to dig down one storey in order to create a basement level, which meant that waterproofing and tanking were essential to the structure’s integrity.

BASF Admixtures

The basement floor slab utilized BASF’s new two-component Watertight System to provide a waterproof substrate for the house. The BASF Watertight System uses conventional products for a single, effective solution to water penetration, with admixtures being introduced at batching stage for total ease and control and rapid, straightforward installation.

The Watertight System combines RheoFIT^® 791, a reactive hydrophobic pore blocking liquid for wet or dry cast concrete, and Glenium^® high-range superplasticising admixtures.

This particular project involved a pour size of 48 m³ for the basement floor slab, with the slab thickness being a minimum of 200 mm. The concrete mix supplied by Tor Multimix, Glastonbury was a RC30 385 kg CEM 1, 20mm pump mix. The 0.45 water/cement ratio was the most onerous of the criteria for the mix, and the target slump was 100-120 mm.

The mix design comprised 1% RheoFIT 791 and 0.5% Glenium^® 123 with the Glenium^® water-reducing admixture being added up front. The mix was dry-batched and RheoFIT 791 was then added at the back end. As the travelling time to site took 40 minutes, the concrete was well mixed by the time of arrival, and a team of three builders oversaw the pour. Membranes installed underneath the concrete gave additional waterproofing.

The Client/Architect designed the property’s walls to be constructed of Insulated Concrete Forms (ICFs), a cost-effective, fast-track construction material with high insulating properties. As one storey of the structure was below ground level, once the blocks were assembled the core was filled with a heavy-weight, self-compacting concrete with waterproofing properties rather than a more typical lightweight infill mix.

The waterproof infill mix necessitated two pours rather than one because the combination of the wall height and the heavy-weight concrete mix increased the level of hydrostatic pressure.