ASTM Cement-Lime Mortar Ratio Chart

Aggregate rule: aggregate measured in a damp, loose condition must be not less than 2¼ and not more than 3 times the sum of the separate volumes of the cementitious materials (cement and lime).

Mortar Type Strength Chart

Mortar Type by Common Masonry Application

Local codes, adopted editions and the structural design can be stricter than these model-code and guidance entries.

Masonry mortar is the material placed between masonry units to bond them into an assembly, make up small differences in unit size, keep the joint continuous, and help resist air and moisture penetration. CMHA describes mortar as a small share of a concrete masonry wall (about 7 percent) with an outsized effect on how the wall performs.

• Cementitious binder: portland or blended cement, or a factory blend such as masonry cement or mortar cement.
• Lime or plasticizers: hydrated lime or lime putty in cement-lime mortar, or the plasticizing materials already blended into masonry and mortar cements.
• Sand: natural or manufactured sand graded for masonry mortar.
• Water: clean water added for a workable consistency.

Mortar and concrete both contain cementitious material, aggregate and water, but BIA cautions against treating them as interchangeable. Mortar is designed around bond, workability and water retention against absorptive units. Concrete is designed to work as a structural material by itself. See the Concrete Mix Ratio Chart for concrete proportions, which follow different rules.

Users often search for mortar recipes when they actually need grout or concrete. The three materials have different jobs, different standards and different consistencies.

ASTM C270 covers four mortar types, M, S, N and O, in each of its two alternative specifications. The types separate mortars by laboratory compressive strength and by the balance of strength, bond and workability. The letter does not describe a single fixed recipe.

• Type M: the highest laboratory compressive strength of the four. BIA describes it as high compressive-strength mortar that is not very workable.
• Type S: general all-purpose mortar with higher compressive and flexural bond strength, used for more demanding structural and exposure conditions.
• Type N: general all-purpose mortar with good bonding capability and workability, widely used above grade.
• Type O: low-strength mortar used mostly for interior applications and restoration, where the code and specification allow it.

CMHA notes that building codes typically require Types M, S and N, and may restrict certain mortars for particular uses. Type O should not be treated as a normal structural or exterior mortar.

ASTM C270-26, the current active edition, gives two alternative ways to specify mortar. Only one should be called for in the project documents, not both.

Proportion Specification

Compliance comes from using the specified materials and adding them to the mixer in the permitted volume proportions. ASTM C270 states that compliance is verified by confirming the materials are as specified, meet their requirements, and are batched in the proper proportions.

Property Specification

A mortar mixture is qualified by preparing it in the laboratory at a specific flow and testing it against the property requirements. The laboratory then establishes proportions from the successful tests, and those proportions are followed when preparing field mortar. CMHA describes this as a preconstruction evaluation.

What Happens When Neither Is Specified?

ASTM C270 says the proportion specification governs, unless data are presented to and accepted by the specifier showing that the mortar meets the property specification.

For cement-lime Type M, the proportion specification is 1 part portland or blended cement and ¼ part hydrated lime or lime putty. Sand is 2¼ to 3 times the sum of the two, which is 2.81 to 3.75 parts for that combination.

• Laboratory property strength: 2,500 psi (17.2 MPa) minimum average at 28 days, for laboratory-prepared mortar only.
• Typical uses: masonry foundation walls and below-grade work, where the IRC requires Type M or S, and heavily loaded structural masonry.
• Workability: BIA notes Type M is not very workable, which affects how easily units can be bedded.
• Limitation: higher compressive strength does not make Type M the best choice for every brick or block. Softer units and many veneer applications do not need it.

For cement-lime Type S, use 1 part cement and over ¼ to ½ part lime, with sand at 2¼ to 3 times their combined volume. At ½ part lime, sand ranges from 3⅜ to 4½ parts.

• Laboratory property strength: 1,800 psi (12.4 MPa) minimum average at 28 days, for laboratory-prepared mortar only.
• Typical uses: foundation walls (Type M or S under the IRC), structural masonry, and stronger brickwork in high-wind and high-seismic areas.
• Seismic: the IRC lists Type M or S portland cement-lime or mortar cement for lateral-force-resisting masonry in SDC D0, D1 and D2.
• Balance: Type S offers higher bond and compressive strength than Type N while keeping better workability than Type M.

For cement-lime Type N, use 1 part cement and over ½ to 1¼ parts lime, with sand at 2¼ to 3 times their combined volume. At 1 part lime, sand ranges from 4.5 to 6 parts.

• Laboratory property strength: 750 psi (5.2 MPa) minimum average at 28 days, for laboratory-prepared mortar only.
• Typical uses: general-purpose brick masonry, most anchored veneer, and above-grade work. BIA recommends Type N for normal use.
• Strengths: good bond, workability and water retention.
• Limitation: Type N is not allowed where the code or drawings require Type M or S, such as prescriptive masonry foundation walls.

For cement-lime Type O, use 1 part cement and over 1¼ to 2½ parts lime, with sand at 2¼ to 3 times their combined volume. At 2 parts lime, sand ranges from 6.75 to 9 parts.

• Laboratory property strength: 350 psi (2.4 MPa) minimum average at 28 days, for laboratory-prepared mortar only.
• Typical uses: interior, nonbearing work and some restoration, where permitted and specified.
• Softer masonry: a lower-strength mortar can suit softer units, but the choice must come from an evaluation, not a rule of thumb.
• Code position: Type O is in ASTM C270, yet building codes typically require Type M, S or N for the structural situations CMHA discusses.

ASTM C270 controls the sand through the total volume of cementitious materials, not through a fixed number. That is why many quoted ratios are examples of a permitted range.

ASTM Aggregate Rule

• Vs: volume of sand, measured damp and loose (parts by volume)
• Vc: volume of portland or blended cement (parts)
• Vl: volume of hydrated lime or lime putty (parts)

Common Shorthand Examples

Sand Range for Selected Lime Amounts

Three cementitious routes appear in ASTM C270. Bag labels and product type matter, so check what is actually in the bag.

A bag of masonry cement is not one part portland cement and one part lime. It already contains plasticizers, and its proportions come from the ASTM C270 masonry cement rows, not from the cement-lime table.

The IRC and ASTM C270 list separate combinations for masonry cement and mortar cement. Aggregate is again 2¼ to 3 times the sum of the separate cementitious volumes, damp and loose.

Masonry Cement Mortar Ratio Chart

Mortar Cement Ratio Chart

Example: 1 part Type N masonry cement plus ½ part portland cement makes Type S. Total cementitious volume is 1.5 parts, so sand ranges from 3.375 to 4.5 parts.

The chart below repeats the ASTM C270 property-specification minimums with metric values. It is a laboratory qualification requirement, so read it together with the next two sections.

Field compressive tests and laboratory property strengths are not the same measurement. Four reasons explain the gap:

• Controlled flow: laboratory mortar is mixed to a prescribed flow, so its water content is set by the test.
• Water chosen for workability: field mortar carries whatever water the mason needs for a plastic mix.
• Absorption by units: absorptive masonry pulls water out of mortar in the wall, lowering its effective water content.
• Different geometry: a thin joint has a very different shape factor than a test cube.

CMHA explains that mortar in the wall is typically stronger than field-tested specimens because of that absorption and joint shape. ASTM C270 states that physical properties of field-sampled mortar are not used to determine compliance and are not acceptance criteria. Field testing under ASTM C780 checks that materials and procedures are consistent from batch to batch.

Mortar compressive strength is not the compressive strength of the masonry assembly (f′m). Wall performance depends on the masonry unit strength, mortar type, geometry, grout, reinforcement, construction quality and the design method used.

TMS 402/602-22, the edition referenced by the 2024 IBC, recognizes both a unit-strength approach and prism testing for establishing masonry compressive strength. A Type M mortar with a 2,500 psi laboratory minimum does not produce a 2,500 psi wall.

Compressive strength is only one of the properties that matter. BIA and CMHA point to several others that often decide field performance:

• Bond: the extent of contact and strength of adhesion between mortar and unit. It rises with mortar strength, though not in direct proportion, and depends on workmanship and unit surface.
• Workability and plasticity: the smooth consistency that spreads easily and holds the unit in place.
• Water retention: the ability to stay plastic against evaporation and absorptive units, which lets a mason lay a bed two or three units ahead.
• Ability to fill irregularities and seal the joint: needed for resistance to water penetration.

Lime improves workability and water retention, which is why increasing cement is not automatically better. Air-entrained materials improve workability and freeze-thaw resistance but reduce bond strength.

ASTM C144 Requirements

ASTM C144-26 covers natural and manufactured sand for masonry mortar. It sets grading limits and requirements such as soundness and deleterious substances. Sand that fails the grading limits may still be used if the resulting mortar meets the ASTM C270 property specification.

• Grading: well-graded sand reduces segregation and improves workability. Sand short on fines gives a harsh mortar, while too many fines can lower compressive strength.
• Cleanliness: dirty sand can harm bond and durability.
• Natural vs. manufactured: natural sand needs less water for the same workability. Manufactured sand has angular particles and needs more water.

Sand Moisture and Bulking

The proportions assume sand measured damp and loose. Moisture makes sand bulk up, so changing moisture between batches changes how much sand a bucket really holds. For volume estimates, the IRC treats 1 ft³ of damp, loose sand as 80 lb of dry sand. Measure with the same container and the same sand condition for every batch. The Masonry Sand Calculator helps with quantity estimates.

Hydrated lime for masonry follows ASTM C207, which designates Types N, S, NA and SA. Types N and S are non-air-entraining, and NA and SA are air-entraining. Type S is the special hydrated lime, with higher early plasticity, higher water retentivity and a limit on unhydrated oxides. CMHA notes Type N or NA lime is not typically used in mortar unless shown by test or performance record not to harm soundness, and BIA recommends only Type S hydrated lime for masonry mortar.

Masonry mortar has no single water-cement ratio. BIA notes that applying the concrete water-cement ratio idea to mortar is misleading, because mortar sits against absorptive units that pull water out of it. Instead, water is adjusted to give a workable, plastic mortar within the approved mix.

• Plasticity: the mix should spread easily and support the unit without slumping.
• Unit absorption: highly absorptive units draw water quickly.
• Weather: heat, wind and sun accelerate water loss.
• Sand moisture and mixer size: both change how much added water is needed.
• Product instructions: follow them for bagged or preblended mortar.

Too much water or too little water can damage bond and durability. CMHA notes that water must be clean and free of harmful acids, alkalis and organic material, and that drinking water is considered suitable.

Above-grade clay brick work is commonly laid with Type N, which BIA recommends for normal use including most anchored veneer. Higher-demand conditions, such as high seismic or high wind areas, typically call for Type S, and some structural or below-grade conditions call for Type M or S.

Brick absorption and unit strength influence how a mortar performs, so no single ratio suits every clay brick. BIA also recommends ASTM C270-compliant mortar and the lowest strength that meets the project requirements. For brick dimensions, coursing and quantities, use the Brick Size Chart and the Brick Calculator.

For concrete masonry, the mortar type comes from the design and the adopted code. CMHA notes that building codes typically require Type M, S or N, that empirical foundation wall design needs Type M or S, and that glass-unit masonry needs Type N or S.

• Bearing and nonbearing walls: follow the structural drawings and specifications.
• Exterior masonry: exposure and wind or seismic demands can push the choice toward Type S.
• Reinforced CMU: mortar bonds the units, while grout (ASTM C476) fills the reinforced cells.
• Foundation walls: Type M or S for IRC prescriptive walls.

Unit dimensions are in the Masonry Block Size Chart, and unit weights are in the Concrete Block Weight Chart.

The IRC requires Type M or S mortar for masonry foundation walls built under its prescriptive foundation wall tables (R404.1.1(1) through R404.1.1(4)). Below grade, mortar faces soil contact, moisture and lateral earth pressure, which is why the code sets a higher minimum than Type N.

Type N or O should not be casually substituted where M or S is required. Foundation walls designed outside the prescriptive tables follow the engineer’s specification. For wall thickness, see the Foundation Wall Thickness Chart.

Brick Veneer and Adhered Masonry Veneer

Anchored brick veneer is conventional masonry, and BIA recommends Type N for most of it. Adhered masonry veneer is a different system: the IRC allows ASTM C270 Type S or N mortar, or latex-modified portland cement mortar complying with ANSI A118.4. Setting mortar behind adhered units and pointing mortar in joints can have different requirements, so follow the product and code instructions for each.

Seismic Areas

• SDC A, B, C: Type M, S or N where the masonry is the lateral-force-resisting system (IRC R606.2.8.2).
• SDC D0, D1, D2: Type M or S portland cement-lime or mortar cement (IRC R606.2.8.3).

Seismic performance comes from the whole structural masonry system: reinforcement, grout, detailing and workmanship. Choosing a stronger mortar alone does not make masonry seismic-resistant.

A hard modern mortar can damage older or softer masonry. Repointing needs an evaluation, not a default recipe.

• Existing unit hardness: mortar should not be much harder than the units.
• Existing mortar characteristics: composition, color and texture affect a match.
• Moisture movement: the joint should let moisture leave the wall at least as easily as the units do.
• Preservation specifications and laboratory analysis: ASTM C1324 covers the examination of hardened mortar.

Do not assume Type O for all old brick. It is one possible lower-strength category where appropriate and specified. Full historic restoration is outside the scope of this chart.

Ratios only mean something when the same container measures every part. For a chosen batch volume V and a mix with total parts P:

Use the approved proportion specification, the manufacturer’s instructions, or the batch established under the property specification. An online ratio is not a substitute.

The checker tests your proportions against the ASTM aggregate rule and the cement-lime lime ranges. The batch volume is the combined volume of loose dry ingredients, not the volume of finished mortar. Weights use IRC conventions: portland cement 94 lb/ft³, hydrated lime 40 lb/ft³, damp loose sand 80 lb dry sand per ft³.

Batch Conversion Chart

One cubic foot equals 7.48 gallons, so a 5-gallon bucket is roughly 0.67 ft³. Use the same bucket, filled the same way, for every part. Bagged products should be batched by the manufacturer’s stated volumes or an approved procedure, since bag sizes vary.

Brick Walls

A geometric estimate works from the wall volume minus the volume of the units:

Job estimating normally uses established unit and joint consumption factors, so treat the geometric method as a check. The Mortar Calculator and Brick Calculator handle project totals.

CMU Walls

CMHA gives typical concrete masonry construction as using about 8.5 ft³ of mortar per 100 ft² of wall, assuming 3/8-inch joints, face-shell mortar bedding and a 10% waste allowance. Do not treat it as universal for every block size, full-bed mortar or different joint thickness.

For block counts and layout, see the Masonry Block Size Chart and the Concrete Block Calculator.

Mortar Joint Thickness

Joint thickness changes both appearance and material quantity. Unless the drawings say otherwise, the IRC (R606.3.1) calls for 3/8-inch head and bed joints, except that the bed joint of the starting course over a foundation must be not less than 1/4 inch and not more than 3/4 inch. The IRC tolerance for load-bearing masonry is plus 1/8 inch for bed joints, and minus 1/4 to plus 3/8 inch for head joints.

Material Measurement and Mixing

1. Confirm the mortar type and the specification method (proportion or property).
2. Verify the materials against the specification (cement type, lime type, sand grading).
3. Measure the cementitious materials accurately by volume or by the approved batching method.
4. Measure the sand consistently in the same damp, loose condition every batch.
5. Add part of the mixing water first, then the dry ingredients, and mix thoroughly.
6. Adjust the water to a workable consistency and keep the batch consistent.
7. Follow the product and project requirements and place the mortar within the permitted working time.

This is a workflow summary, not a substitute for the project specification on structural work.

Mixing Consistency and Pigmented Mortar

Batch consistency matters most with colored mortar. BIA recommends careful control of pigment quantity and consistent batching, since small changes in water, materials, tooling or curing can change the color. CMHA notes that TMS 602 limits pigments to no more than 1 to 10 percent by weight of cement, depending on the pigment type. Pigment does not by itself change the M, S, N or O classification.

Retempering

Retempering restores workability by mixing in water lost to evaporation, before the mortar has stiffened from hydration. It is different from reusing mortar after initial set, which is not acceptable. BIA gives 2½ hours after initial mixing for normal and cold weather and 2 hours for hot weather. For glass-unit masonry, the IRC forbids retempering after initial set and requires discarding mortar not used within 1½ hours of initial mixing. For ordinary masonry, follow TMS 602 and the project specification.

TMS 602 sets temperature-dependent provisions for hot and cold weather, and BIA Technical Note 1 summarizes them for brick masonry. Values below are a summary of BIA Technical Note 1, so confirm them against the current TMS 602 edition and the project specification.

In cold weather, mix mortar in smaller batches so it can be used before it cools, and protect newly built masonry as required. In hot weather, watch for fast water loss and fog-spray newly built masonry as the specification requires. Cold-weather construction is also affected by footing depth and frost, covered in the Foundation Frost Depth Chart.

• Preconstruction qualification: under the property specification, laboratory testing establishes the approved proportions.
• Material verification: confirm cement, lime and sand match the specification (ASTM C270 compliance is verified by materials and batching).
• Batch proportions: observe that ingredients are added in the specified proportions.
• ASTM C780: preconstruction and construction evaluation of mortars, used to verify consistency of materials and procedures.
• ASTM C1324: examination and analysis of hardened mortar, including petrographic analysis.
• Laboratory testing: the property specification requires an evaluated testing agency (ASTM C1093).

Field compressive specimens are useful for checking consistency, not for treating ASTM C270 laboratory property strengths as field acceptance criteria.

1. Identify the masonry unit type.
2. Decide whether the wall is structural or veneer.
3. Determine above-grade or below-grade exposure.
4. Identify the locally adopted code and edition.
5. Check the structural drawings and specifications.
6. Determine the seismic design category.
7. Identify unit strength and absorption.
8. Select the lowest mortar strength that satisfies the requirements.
9. Choose the approved cement-lime, masonry cement or mortar cement system.
10. Follow the ASTM C270 proportion or property specification, not a hybrid mixed on site.

Project specifications, the adopted code and its edition, ASTM standards, TMS 402/602 requirements and manufacturer instructions govern. Code entries here refer to the IRC; other codes and local amendments can differ. Shorthand ratios are examples, not specifications, and calculated tables are illustrative.

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