Mason lime: Type S hydrated lime for mortar

Mason lime (Type S): what we stock

What does lime do in mortar?

Cement brings strength. Lime brings the working qualities. According to the lime makers, Type S lime keeps water in the mortar so it doesn't dry out against thirsty block, carries more sand, spreads with a smooth, sticky feel and improves bond between the mortar and the units.

Lime also keeps the hardened mortar slightly flexible, and as it takes up carbon dioxide over time it can seal fine hairline cracks. Cement-lime mortar, meaning portland cement, lime and sand with no additives, is the standard mortar in ASTM C270.

What is the difference between Type S and Type N lime?

ASTM C207 covers four hydrated limes for masonry: Type N (normal), Type S (special), and air-entraining versions of each, NA and SA. The S stands for special, not for Type S mortar.

Type S and SA differ from N and NA mainly in three ways: they must develop high plasticity early, they must hold more water, and their unhydrated oxide content is capped. Lime makers produce Type S from dolomitic limestone, hydrated under pressure.

Source: National Lime Association fact sheet on hydrated lime for masonry. The unhydrated oxide cap applies to Types S and SA only.

Mortar types M, S, N and O by volume

Field-mixed mortar is batched by volume under the ASTM C270 proportion method. The ratios below are cement to lime to sand. The strengths are typical lab results reported by the National Lime Association, with the C270 property minimums alongside.

Mortar shouldn't be stronger than the units it joins. The specification or engineer sets the type; NLA's general guide lists N for most above-grade walls and S for exterior work at or below grade.

What to order with mason lime

For site-mixed mortar, order lime and 94 lb Portland cement together. Crews who want a preblended bag take 80 lb mason mix type S or mortar mix instead. The same lime goes into scratch and brown coats of portland cement stucco, where it cuts cracking and helps the coats bond.

Keep bags dry and off the ground. Lime, cement, mixes and sand can all ride on one delivery from Monroe.

Questions about mason lime (Type S)

What is Type S lime for?

Type S hydrated lime is mixed with portland cement and sand to make mortar and stucco. It makes the mix more workable, holds water so the mortar doesn't dry out against absorbent block, and improves bond to brick, block and stone. Yankocy stocks Type S mason lime meeting ASTM C207 in 50 lb bags, 50 bags per pallet.

What does Type S mean in lime?

In ASTM C207, the S stands for special. Type S hydrated lime must develop high plasticity early, hold at least 85% water retention and contain no more than 8% unhydrated oxides. It has nothing to do with Type S mortar; Type S lime goes into Type M, S, N and O mortars.

What is the difference between Type N and Type S hydrated lime?

Both are ASTM C207 masonry limes. Type S must reach high plasticity early, hold more water, and stay under a cap on unhydrated oxides. Type N isn't held to those limits. That's why masons and stucco crews usually ask for Type S.

What are the three types of lime?

In building, lime usually means quicklime, hydrated lime or hydraulic lime. Quicklime is burned limestone. Hydrated lime is quicklime slaked with water, sold as a dry powder; mason lime is this kind. Hydraulic lime sets partly by reacting with water.

Why is lime mortar no longer used?

Straight lime-and-sand mortar hardens slowly, by taking in carbon dioxide from the air. Modern mortar adds portland cement for early strength. The lime is still there: cement-lime mortar is the standard mortar in ASTM C270, and lime gives it workability, water retention and bond.

Last updated November 2, 2026

Yankocy sells mason lime wholesale to mason and lumber yards, on the same truck as cement and bagged mixes. Buying for your own home? Your local lumber or mason yard can order it for you.

Mason lime (Type S) data sheets and sources

• Graymont: Dolomitic Hydrated Lime Type S, safety data sheet
• National Lime Association: Hydrated Lime for Masonry Purposes (fact sheet)
• Carmeuse: The Benefits of Type S Mason's Lime
• ASTM C207: Standard Specification for Hydrated Lime for Masonry Purposes

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