How many blocks will one 80 lb bag of mortar lay?

One standard 80 lb (36.3 kg) bag of pre-blended Type S or Type N masonry mortar will lay approximately 30 to 35 standard 8x8x16-inch concrete blocks with nominal 3/8-inch bed and head joints using face-shell bedding. Mason contractors typically estimate 3 bags per 100 blocks (or 1 bag per ~33 blocks) including typical 10% spillage waste.

Should I use Type S or Type N mortar for concrete block walls?

Per ASTM C270, use Type S mortar (1,800 psi compressive strength) for below-grade foundation walls, retaining walls, structural masonry, and high-wind structural applications. Use Type N mortar (750 psi) for above-grade interior partitions, decorative veneers, and garden walls where high lateral shear forces are absent.

What is the difference between mortar and concrete core grout?

Mortar (ASTM C270) is a bonding adhesive applied only to the horizontal bed and vertical head joints to glue blocks together. Grout (ASTM C476) is a high-slump, pourable concrete mixture (usually 8 to 11 inch slump) containing pea gravel that is poured directly into the hollow vertical cores of the CMU blocks to encapsulate structural steel rebar.

How much sand and masonry cement is needed if mixing on site?

For field-mixed mortar using ASTM C91 masonry cement, use a volume ratio of 1 part masonry cement to 2.25 to 3.0 parts damp, loose masonry sand (ASTM C144). One 70-lb bag of masonry cement mixed with 240 lbs of damp sand produces approximately 2.8 cubic feet of wet mortar, laying roughly 75 to 80 standard 8-inch blocks.

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MASONRY SPECIFICATION MANUAL

Mortar Calculator for Concrete Blocks

Estimating mortar is one of the easiest ways for a masonry budget to go off track. This guide explains how to calculate pre-blended 80 lb and 60 lb bags of Type S, N, and M mortar per 100 CMU blocks, accounts for 3/8-inch joint loss, site-mixed sand ratios (ASTM C270), and differentiates joint mortar from structural core grout (ASTM C476).

Author: Construction Estimator Team • Standards: ASTM C270 / ASTM C476 / TMS 402 • Updated: October 2026

■ Quick Fact Summary ✓ ASTM C270 & C476

One 80 lb bag of pre-mixed Type S mortar lays approximately 30 to 35 standard 8×8×16 concrete blocks with 3/8-inch joints and face-shell bedding. Masonry estimators use the standard rule of 3.2 bags per 100 blocks (or 1 bag per ~33 blocks).

Bags / 100 Blocks3.2 bags (80 lb)

60 lb Equivalent4.5 bags / 100

Standard Joint3/8 in (9.5 mm)

Grout (Solid Cores)0.96 yd³ / 100 blks

■ Interactive Mortar Estimator

Our main calculator engine automatically estimates your exact mortar requirements (~33 blocks per 80 lb bag) alongside block takeoffs in real time:

Open Real-Time Takeoff Engine ↗ View Bag & Sand Requirement Table ↓

FIG. 02 — Face-Shell Bedding vs Core-Fill Grout Anatomy

1. Comprehensive Mortar Bag & Bulk Material Matrix

The table below outlines the exact number of pre-mixed bags or site-mixed raw ingredients needed based on nominal 8×8×16-inch hollow CMU blocks laid with standard 3/8-inch (9.5 mm) joints and face-shell bedding, including a standard 10% spillage and waste allowance:

Block Quantity	Wall Area (8×8×16)	80 lb Pre-Mix Bags	60 lb Pre-Mix Bags	Masonry Cement (70 lb)	Masonry Sand Needed
50 Blocks	~44 sq ft	2 bags	3 bags	1 bag	250 lbs (~0.1 cu yd)
100 Blocks	~89 sq ft	3.2 bags (buy 4)	4.5 bags (buy 5)	1.5 bags (buy 2)	500 lbs (~0.2 cu yd)
250 Blocks	~222 sq ft	8 bags	11 bags	3.5 bags (buy 4)	1,250 lbs (~0.5 cu yd)
500 Blocks	~444 sq ft	16 bags	21 bags	7 bags	2,500 lbs (1.25 tons)
1,000 Blocks	~889 sq ft	31 to 33 bags	42 to 45 bags	13 to 14 bags	5,000 lbs (2.5 tons)

2. ASTM C270 Mortar Types: S vs N vs M

Under ASTM C270 (Standard Specification for Mortar for Unit Masonry), mortar types are defined using every other letter in the phrase MaSoN wOrK:

Type M (2,500 psi): High Strength & Heavy Compressive Load. Formulated with a high Portland cement ratio. Ideal for foundations bearing extreme vertical loads, earth-retaining walls with heavy surcharge, and masonry structures subjected to continuous freeze-thaw cycles or water saturation.
Type S (1,800 psi): High Flexural Bond Strength (Contractor Standard). The most common mortar specified for CMU block walls. Offers superior tensile and lateral bond strength to resist wind loads, seismic events, and soil pressures.
Type N (750 psi): Medium Strength & High Workability. Used primarily for above-grade, non-loadbearing interior partition walls, chimney veneer, and soft brick restoration where high flexibility and vapor permeability are required.

3. Mortar (ASTM C270) vs Core Grout (ASTM C476)

Critical Estimating Difference:

A frequent error made by DIY builders and apprentice estimators is confusing joint mortar with cell grout:

Mortar has a thick, peanut-butter consistency and is applied only to the 1-1/4 inch outer perimeter face shells of the block. It bonds adjacent units together.
Grout is a wet, fluid mix (8–11" slump) made of fine aggregate or 3/8" pea rock. It is poured down the vertical hollow holes to encapsulate steel rebar. For 8-inch CMU blocks, one filled core requires approximately 0.25 cubic feet of grout (or ~1 cubic yard of ready-mix grout per 108 cores filled).

4. Mixing Mortar from Scratch (Proportions)

When mixing mortar on-site with a gas paddle mixer or wheelbarrow rather than buying pre-blended sacks:

Type S Mix Ratio: 1 part Portland Cement + 1/2 part Hydrated Lime (ASTM C207) + 3-1/2 to 4-1/2 parts clean, damp Masonry Sand (ASTM C144).
Masonry Cement Method: 1 bag of Type S Masonry Cement (70 lbs) + 2.5 to 3.0 cubic feet of damp sand + clean potable water until the trowel holds a ridge without slumping.

5. Masonry Tool & Trowel Essentials

Mixing & Transport

Heavy-gauge steel wheelbarrow or mortar pan
Square masonry hoe with dual holes
Rubberized mortar boards & folding stands
Clean measuring buckets for consistent water dosage

Laying & Finishing

10" or 11" London or Philadelphia pattern trowel
Convex barrel jointer (3/8" and 1/2" radiuses)
Corner blocks and line stretchers with nylon line
Soft horsehair masonry dusting brush

Explore Connected Planning Guides

Ensure your materials and dimensions line up before ordering:

Retaining Wall Block Calculator — Buried courses, base trenches, and backfill gravel.
Concrete Block Weight Chart — Unit and pallet weights for flatbed delivery hauling.
CMU Block Sizes & Dimensions — Actual vs nominal sizing with 3/8" mortar allowance.
Cinder Block Pallet Quantities & Cost — Wholesale pallet pricing and block counts.