Monday, 10 May 2010
The lime mortar cast within the formwork was completed today as planned. It was thicker than we had hoped in places. Ideally we were trying to keep it to a minimum, just sufficient to provide a level base to begin the masonry from. We were aiming for less than 50mm but generally it seems to be between 50-100mm.
We wanted to backfill around the concrete lintels with spoil first before applying the limecrete bed to avoid the lime mortar becoming thicker here. However, the mortar does seem to be a bit thicker.
The problem with the mortar becoming too thick is that it will increase the drying time and we were hoping to start laying the first phase of masonry after about 36hours in order to stay on programme.
We are using NHL 5 lime mortar, with a mix of 1 (lime) : 2.5 (sharp sand). The sand needs to be well graded, and include a good range of all grain sizes from large to very small. This will give the mortar good strength. The sand we are using is from Whitton Frost in Bury and includes grain sizes from 4mm down.