C. Strunk Inc

‼️ ⚠️ TECHNICAL POST ⚠️ ‼️

🔥Below is a very short snippet of some very basic lime chemistry:

Why Lime Mortar Is Vulnerable to Dissolving

Pure Carbonating Lime mortar is made from calcium hydroxide that slowly carbonates over time and turns into calcium carbonate (CaCO₃), the same material as natural limestone. This gives the mortar its breathability and flexibility — essential qualities for historic masonry.

However, calcium carbonate reacts with acid including weak acids. One often overlooked acid is called: carbonic acid (H₂CO₃), which forms when carbon dioxide dissolves in water:
CO₂ + H₂O → H₂CO₃
CaCO₃ + H₂CO₃ → Ca(HCO₃)₂ (soluble calcium bicarbonate that leaches away)

Put into plain language: The water molecules that are in rain drops, fog, moisture in the soil, etc, have both a positive and negative ion which are constantly attracting electrically neutral carbon dioxide molecules. When a water molecule and a carbon dioxide molecule combine, they create a new substance called carbonic acid (H₂CO₃).

Carbonic Acid is what actually dissolves the lime in your historic lime mortars and plasters.

Adding pozzolan to the carbonating mortar will create a more durable mortar for consistently wet and damp locations. The recipes are simple but complex.

This picture shows remnants of original striping. The brick was lime washed red then someone with patience went back and painted the mortar joints white. It was very common throughout Lancaster County PA