I do not think it is advised, to lay blockwork in the sleet but I have a hunch that there is no severe cold spell on the horizon that could ruin a newly laid wall. Jordan and I busied ourselves building the blockwork foundations for the new barn. Poor Jordan had cold feet all day and the grey wet damp conditions did little to lift the spirits. You cannot see much in the attached photo as everything is covered from the rain and forecast snow. Imagine however, the sunshine and some grass where you see rain and mud!