Abstract Surface treatment technology is instrumental to construction material conservation and more specifically to preventing decay and improving durability. Surface treatments help protect and consolidate the built heritage against material damage, reducing repair and replacement costs. This study assessed the effect of two eco-friendly healing agents, one generated by iron-enriched Escherichia coli and the other by mixed microbial cultures that metabolise glycerol, a biodiesel processing by-product, to produce polyhydroxyalkanoates. Healing was monitored by measuring the water drop absorption rate in cement mortar, air lime mortar, ceramic brick, limestone, adobe and compressed earth block. The agents tested lengthened water absorption times in all the materials studied, confirming their efficacy as external repair treatments for construction materials.