Naylor Concrete Lintels R6 is the best concrete lintels on the market in the UK. To ensure maximum efficiency, all units are pre-stressed and come with a standard fire rating of 30 minutes. A wet cast concrete finish with an ex-steel mould finish. These units are ideal for use below ground due to additives. Different form and location of reinforcement than in the Naylor economy range. Tiny air holes may appear on the surface, and aggregate and concrete fines may settle to the floor. Normally used in plastered, non-exposed cases.