Mixed my first batch of lime mortar for a historic restoration project. Got it on my hands without gloves. That burning sensation taught me to respect the material. Also taught me to wear protection.
What Hydrated Lime Is
Quickite – raw calcium oxide from heated limestone – reacts violently with water. Add water carefully and you get hydrated lime, a white powder that’s still caustic but more manageable. Construction grade is often called mason’s lime.
Different from agricultural lime, which is just ground limestone. Hydrated lime has been chemically changed and behaves differently.
Why It Matters for Buildings
Lime mortars flex. Portland cement mortars don’t. Old brick and stone buildings were built with lime. Repointing them with hard cement mortar causes the softer masonry to crack instead of the joints absorbing movement.
Lime also self-heals to some extent. Small cracks can fill themselves as lime reacts with carbon dioxide over time. Portland cement just cracks and stays cracked.
Construction Uses
Mortar – Mixed with sand for laying brick and stone. Traditional ratio is often 1:3 lime to sand, but this varies. Lime mortars take longer to cure than cement but age better.
Plaster – Interior and exterior finish coat material. Lime plaster breathes, allowing moisture to move through walls rather than trapping it.
Whitewash – Lime mixed with water makes a traditional paint. Antiseptic and breathable. Common on historic buildings and in agricultural settings.
Soil Stabilization
Mix hydrated lime into clay-heavy soil and it changes the chemistry. The clay becomes less plastic, more stable, better able to support loads. Road builders use this technique for subgrades.
Works for foundations too on marginal sites where the soil needs improvement before construction.
Water Treatment
Municipal water plants use hydrated lime to adjust pH. It softens hard water by precipitating calcium and magnesium. Old-school technology that still works well.
Safety Matters
This stuff is strongly alkaline. It burns skin, especially wet skin. Damages eyes seriously. The powder irritates lungs if inhaled.
Wear gloves, eye protection, and a dust mask when handling it. If it gets on you, wash immediately with plenty of water. Not something to be casual about.
Storage
Keep it dry. Hydrated lime absorbs moisture from air and turns into calcium carbite over time, which is useless for most applications. Store in sealed containers away from humidity.
Check the date on bags. Old product may not perform like fresh material.
When to Use It
Historic restoration where matching original materials matters. Projects where flexibility is more important than initial strength. Situations where breathability prevents moisture problems.
Modern construction uses less lime than it should, honestly. The old builders knew things we’ve forgotten.
