Intumescent coating added to existing structure

Hello Samuel and thank you for utilizing ASK Hilti! The IFRM can be applied to an existing structure as long as the primer is determined to be well adhered to the substrate showing no signs of being compromised due to rust, curling, delamination, flaking,etc. The existing primer is an approved primer and well adhered to the substrate. To determine well adherence, there are adhesion tests that be performed in accordance with ASTM D 3359 Method A to determine if the primer is suitable to overcoat. An approved primer list can be downloaded from our website at www.us.hilti.com/steel-protection.