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Compounds and Cleaning · Formula · Book recipe 8.4

Lime mortar and plaster (hydrated lime)

Lime-based mortars and plasters predate modern cement by thousands of years and remain in use because they flex without cracking, breathe moisture, and actually harden further over decades.

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How it works

Mix dry
Add water
Apply thin coats
Cures for weeks

Inside this article

What you'll need
Steps
Warnings
Storage and shelf life

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  • The method at a glance: mix dry, then add water, then apply thin coats, then cures for weeks
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Prefer paper? This is Recipe 8.4, page 38, in Prepper's Chemical Survival Guide.

Questions this answers

Tap a question for the short answer.

How do I make lime mortar?

Hydrated lime is blended with clean fine sand, and optionally a little clay for adhesion, then wetted to a trowelable paste. It hardens by reabsorbing carbon dioxide from the air, which lets it flex and breathe.

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What's the recipe for lime plaster?

Lime plaster uses the same lime and sand paste as the mortar, built up in several thin coats instead of a single thick layer. Each coat is dampened before the next so the layers bond.

Members get the exact amounts and every step.

How long does lime plaster take to cure?

It dries coat by coat, but full hardening is slow because lime cures by pulling carbon dioxide back out of the air. Fresh work needs protection from rain while it sets.

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Can I patch a cob oven with hydrated lime?

Only on parts that never touch flame. The lime mix is for patching and sealing surfaces away from fire, not for the inside of a firebox.

Members get the exact amounts and every step.

How long does hydrated lime last in storage?

The dry powder keeps indefinitely as long as it stays sealed away from moisture, air, and acids. Mixed mortar does not store, so make it fresh each time.

Members get the exact amounts and every step.

Keep going

Read nextCalcium HydroxideA strong alkaline base, also called slaked lime. It preserves eggs, raises low soil pH, sanitizes with whitewash, and binds simple mortar and plaster.Compounds and Cleaning · Compound

Related to this

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Everything in Compounds and CleaningNever-mix checkerShelf life tableFind a recipe by needWalk-around auditStart here

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Compounds and Cleaning · FormulaSource: Prepper's Chemical Survival Guide, Recipe 8.4, p. 38 · Last reviewed 2026-09-18

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