Hydrated lime, or calcium hydroxide, is a compound that forms naturally inside concrete as cement reacts with water. It’s part of what holds concrete together. Densifiers react with it to harden the surface, and acid stains get their color by reacting with minerals in the cement. The amount available varies from slab to slab, which affects how treatments take.
Why Hydrated Lime Matters for Your Floor
You won’t see it, but the lime in your slab affects two common finishes:
- Polishing. A densifier reacts with the calcium hydroxide and changes it into a stronger material, a bit like a sponge filling in and stiffening.
- Staining. Acid stain gets its color by reacting with the cement on the surface. Because every floor contains different amounts of minerals, two slabs can take the same stain differently.
It’s also what acids attack. Vinegar and other acids react with the calcium hydroxide in cement paste, which is why acidic cleaners etch concrete.
What It Means When You Hire a Contractor
You don’t need to test for lime yourself. What it means for you is that results vary by slab. Ask for a test patch before a stain job so you see your own floor’s color, and ask how the crew preps the surface. Our concrete floor staining guide explains the rest.
Hydrated Lime FAQ
What is hydrated lime used for?
As a bagged product, it has building and garden uses. Inside concrete, it forms on its own as the cement cures, and it’s what densifiers react with.
Is hydrated lime the same as regular lime?
No. Agricultural lime is calcium carbonate and much slower to react. Hydrated lime is a strong base that can cause chemical burns, so handle the bagged product with gloves and eye protection.