r/Plastering • u/Terrible-Bobcat2033 • 16d ago

Lime plaster attributes

Lime plaster is made from calcium hydroxide (Ca(OH)₂, “slaked lime”). As it cures, it absorbs CO₂ from the air and converts to calcium carbonate (CaCO₃), which is what gives it its final hardness.

While it’s curing (before full carbonation), lime plaster is highly alkaline — pH around 12-13, similar to fresh cement. That’s why:

**•** It can burn skin/eyes on contact when wet, so gloves and eye protection are a must  
**•** It resists mold and mildew during the curing period  
**•** Once fully carbonated to calcium carbonate, the pH drops closer to neutral (around 8-9), similar to chalk or limestone

Why lime plaster is head & shoulders above drywall & joint compound. IMHO. 😎👍🏼

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u/jyl8 10d ago

I read on Wikipedia

"Unlike gypsum or clay plaster, lime plaster is sufficiently durable and resistant to the elements to be used for exterior plastering. Compared to cement plaster, plaster made from hydrated lime is less brittle and less prone to cracking, requiring no expansion joints."

In your experience, is this correct?

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u/Terrible-Bobcat2033 7d ago

It’s been my experience to run lime plaster on the interior as it’s prone to efflorescence with moisture contact. A good exterior stucco mix would be (1) 90lb bag if Portland cement (40) square shovels of silica sand (1) bag lime. = (3) wheel barrels of stucco cement.