Our recommended solution for this situation would be to ensure that where any bracketry is connected to the structural steel, these locations should coincide with the board joints for the steelwork encasements. This will allow the encasement boards to be notched around the ties with the smallest possible gaps between the ties and the boards – between 3mm and 6mm as a maximum. Any small remaining gaps can then be sealed with a FSi Promat Pyrocoustic® Sealant for dry internal environments, or FSi Promat Pyrolastic® Silicone Sealant for any areas subject to moisture/atmospheric conditions. 

We would recommend that the maximum cross-sectional area of the brackets is kept below 3,000mm2 per linear meter of encasement, this is in accordance with industry guidance from the ASFP in their Advisory Note 21: ASFP Position on Coatback with Respect to Attachments and Unprotected Secondary beams fixed to Protected Primary Beams.