Lime-based mortars with linseed oil: sodium chloride resistance assessment and characterization of the degraded material

Abstract

Lime mortar is often used to repair historic buildings but is prone to salt crystallization with deleterious consequences. Lime mortar is a very susceptible material due to its high porosity and low mechanical resistance. Recent findings concerning mortar additives that impart hydrophobic properties to mortar show that by limiting water penetration, damage from frost and salt can be decreased. Linseed oil was commonly used in former times as an additive for mortar in order to grant hydrophobicity. The aim of the present research is to assess the ability of lime -based mortars with 1.5% linseed oil (by the weight of the binder) to resist salt degradation. The effect of linseed oil addition was  studied  in  two  different  mortar  mixtures:  air  lime  mortar  and  air  lime -metakaolin  mortar. Specimens, cured for three months, were subjected to a sodium chloride ageing test. The ageing action was evaluated by means of mechanical and physical measurements. Addition of 1.5% of oil to both mortars resulted in remarkable water absorption reduction without significantly affecting their mechanical strength. Improved durability of lime-based mortars with added linseed oil has been confirmed, making the present formula a recommended recipe for mortar repairs.