How many bags of mortar do I need for 100 blocks?

Laying 100 standard 8x8x16 concrete blocks requires 3.0 to 3.5 bags of 80 lb Type S or Type N mortar mix with standard 3/8" joints.

What is the best mortar for exterior block and brick walls?

Type S mortar (1,800 PSI) is the industry standard for exterior block walls, retaining walls, and foundation work due to high flexural bond strength.

Can I use concrete mix instead of mortar for laying blocks?

No. Concrete contains coarse gravel stones that prevent achieving a thin 3/8" joint. Mortar contains fine graded sand and hydrated lime for a buttery, airtight bond.

How much water is needed per 80 lb bag of mortar mix?

An 80 lb bag of pre-blended mortar requires approximately 4.5 to 5.5 quarts of clean water until it clings firmly to an inverted trowel.

Construction • Material Estimator

Mortar & Concrete Bag Calculator

Calculate exact premix bags of Type S/N mortar for block/brick walls, and fast-setting concrete bags for fence and gate posts

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Mortar vs Concrete: Key Differences Explained

What is Mortar?

Mortar is composed of Portland cement, hydrated lime, and fine masonry sand with NO gravel aggregate. It acts as the "glue" that bonds concrete blocks, bricks, or stones together and seals joints against water intrusion. Never use structural concrete mix as a block bonding bed.

Setting Fence Posts with Fast-Setting Concrete

Fast-setting concrete (such as Quikrete Fast-Setting in the red bag) allows you to set posts without pre-mixing in a wheelbarrow. Pour the dry powder directly around the plumb post in the hole, then pour 1 gallon of clean water on top. It hardens in 20–40 minutes.

Frequently Asked Questions (FAQ)

Laying 100 standard 8" × 8" × 16" concrete blocks requires approximately 3.0 to 3.5 bags (80 lb) of pre-blended Type S or Type N masonry cement with standard 3/8-inch face-shell joints. If using 60 lb bags, you will need approximately 4.2 to 4.5 bags per 100 blocks.

A standard 4x4 or 2-3/8" steel fence post in a 10-inch diameter hole dug 36 inches deep requires 3 to 4 bags (50 lb) of fast-setting concrete mix. Remember to place 4 inches of gravel at the bottom of the hole for drainage before setting the post.

Type S mortar (1,800 PSI) is the industry standard for exterior structural masonry, retaining walls, foundation CMU walls, and below-grade construction due to its high compressive and lateral flexural bond strength. Type N (750 PSI) is best for non-load-bearing exterior veneers, interior walls, and chimneys.

No. Never use concrete mix to lay bricks or concrete blocks. Concrete contains coarse gravel stones that prevent achieving a thin, uniform 3/8-inch bed joint. Mortar contains fine graded sand and hydrated lime, which provides the plastic "buttery" consistency required for mason tools and creates an airtight, water-resistant seal.

An 80 lb bag of pre-blended masonry mortar mix requires approximately 4.5 to 5.5 quarts (1.1 to 1.4 gallons) of clean drinking water. Add 75% of the water first, mix for 3 minutes, then gradually add the remaining water until the mortar clings firmly to an upside-down trowel without sliding off.