Laying Block and Brick

Masonry looks simple. You spread mud and stack units. In practice, a mason is working within 1/8 inch over a long wall, to a line, while the mortar is curing under their hands. A wall that is level and plumb in the corners and has full joints lasts a century. One with poor joints leaks and cracks, and a fresh wall that is not braced can blow over.

This guide covers concrete masonry units (CMU, or block), and brick veneer and walls. Plans, specifications and local code control the reinforcement, mortar type and details for your job.

What You Will Be Able to Do

• Read block and brick sizes, nominal and actual.
• Select a mortar type and mix it correctly.
• Lay a corner lead, run a line and tool joints.
• Describe how masonry walls are reinforced and drained.
• Set up a limited access zone and bracing for a wall in progress.

Block and Brick Sizes

A block's nominal size includes one mortar joint. Its actual size does not.

The difference is a 3/8-inch mortar joint, which is the standard thickness. Two courses of block with their joints rise 16 inches. Three courses of modular brick rise 8 inches, so brick and block line up.

Special units include corner blocks, bond beam or lintel blocks for grout and rebar, and split-face blocks for a textured look.

Mortar

Mortar bonds units together, seals joints and takes up small size differences. It is not concrete, and it is designed to be weaker than the block so that any cracks stay in the joints.

Type S is the usual choice for above-grade load-bearing walls, and Type N is common for veneer. A common proportion for Type S by volume is 1 part Portland cement, 1/2 part hydrated lime, 4-1/2 parts sand. Many crews use premixed bags.

Mixing:

1. Add most of the water to the mixer first.
2. Add half the sand, then the cement and lime, then the rest of the sand.
3. Mix for at least 3 to 5 minutes.
4. Adjust water so the mortar hangs on the trowel without sliding off.

Mortar stiffens from evaporation and from setting. You can add a little water to mortar that has dried out, which is called retempering. Discard mortar once it is about 2-1/2 hours old, because at that point it has started to set.

Warning: Mortar is caustic, like wet concrete. Wear gloves and eye protection, and wash your skin right away if it gets on you. Cutting block or brick creates silica dust. Use a wet saw or a saw with a vacuum, and wear respiratory protection where required.

Laying a Block Wall

1. Lay Out

Snap a chalk line on the footing for the wall face. Dry-lay the first course to check the fit and plan where cuts go, so you do not end with a sliver. Openings should fit whole or half units when possible.

2. Set the First Course

Spread a full bed of mortar on the clean footing. Bed joints at the footing can be thicker to take up unevenness, generally up to about 3/4 inch. Set the corner block first, level it and plumb it, then lay out from there.

3. Build the Corners

A lead is a corner built up first in steps, called racking back. Corners are the most important part of the wall because everything between them follows the line set from them.

1. Build the corners up 3 to 5 courses.
2. Check each course with a level for level and plumb.
3. Check course height with a story pole, a rod marked at each course height. Eight inches per course for block.
4. Check diagonal alignment across the rack with a straightedge.

4. Run the Line

Stretch a mason's line between the corners at the top of the next course. Hold it with line blocks or pins. Keep it tight, so that it does not sag.

5. Lay to the Line

1. Spread mortar on the face shells of the block below. Block has a thicker side, which goes up to give you more bed for the mortar.
2. Butter the ends of the block you are setting. This is the head joint.
3. Set it down near the line and press it into place.
4. Tap it to height so the top edge is just shy of the line without touching it.
5. Cut off squeezed-out mortar with your trowel.

Keep checking. Do not move a unit once the mortar has started to set, as that breaks the bond. Take it out, clean it and lay it again with fresh mortar.

6. Tool the Joints

Wait until mortar reaches thumbprint hardness, which means your thumb leaves a clean print without mortar sticking to it. Tool the joints with a jointer. Tooling compresses the mortar to make it denser and seal it against the block. Concave joints and V joints shed water best. Raked joints hold water, so they are not used in weather-exposed work.

Brush off any crumbs after tooling, once the mortar is firm.

Reinforcement and Grout

Plain masonry is strong in compression but weak in bending, so walls that carry wind and soil loads need steel.

• Vertical bars. Set in block cells at the spacing shown on the plan.
• Joint reinforcement. Ladder or truss wire laid in the bed joints, commonly every other course, or every 16 inches, for crack control.
• Bond beams. Horizontal courses of U-shaped blocks filled with bars and grout, at the top of the wall and over openings.
• Lintels. Beams over doors and windows that carry the wall above.

Grout is a fluid mix that fills the cells around the steel. It is not mortar. Keep cells clean. Pour in the lift height the specification allows, and consolidate it with a small vibrator. Low-lift grouting is commonly done in pours of up to about 5 feet. Check the spec.

Laying Brick

Brick follows the same principles as block, with a few extras.

• Bonds. Running bond (each joint centered over the unit below) is by far the most common. Flemish, English and stack bond are mainly decorative.
• Veneer. In modern houses, brick is usually a single layer in front of a wood or steel wall, with a 1-inch air space behind it. It carries only its own weight.
• Wall ties. Metal ties attach the veneer to the backup wall, commonly every 16 inches up and 24 to 32 inches along. Check the code for your wall. The IRC limits each tie to 2.67 square feet of wall.
• Flashing. Water will get behind brick. Through-wall flashing at the base and above openings catches it.
• Weep holes. Openings at the base and above flashing let the water out. Space them no more than 33 inches apart, and many crews use about 24 inches. A blocked weep can leak into the building.

Keep the air space clean of mortar droppings. Use a mortar net or a board to catch them.

Safety Around Rising Walls

Limited Access Zone

OSHA rule 1926.706 requires a limited access zone before work on a masonry wall begins:

• It must be on the side of the wall with no scaffold.
• It must run the full length of the wall.
• It must be as wide as the wall will be tall, plus 4 feet.
• Only people actively building the wall may enter.
• It stays in place until the wall is supported against overturning.

Bracing

Masonry walls over 8 feet tall must be braced to prevent overturning and collapse unless they have enough support. The bracing stays until permanent supports, such as a roof or floor, are in place. Green mortar has very little strength, so a gust of wind can push a new wall over. Follow the wall bracing plan, and stop work and clear the zone if the wind exceeds its limit.

Lifting

Block usually weighs about 35 pounds each. Mortar tubs and bags are heavy as well. Stage material within easy reach, keep it off the ground, and use mechanical help and a two-person lift where you can.

Scaffolds

As a wall rises, masons work on scaffolds. Heavy loads of block and mortar on a platform must stay within its rating. Do not stack material all in one bay.

Troubleshooting

Check Your Understanding

1. A plan calls for a wall that is 10 courses of standard block. How tall is it?

10 x 8 inches = 80 inches, or 6 feet 8 inches.

2. You press your thumb on a joint and it comes away with mortar on it. What does that tell you?

It is too soon to tool. Wait for thumbprint hardness, when your thumb leaves a clean print.

3. You bump a block after the mortar has stiffened. How do you fix it?

Remove it, clean off the old mortar, and relay it in fresh mortar. Tapping a stiffened unit breaks the bond.

4. A 20-foot-tall wall is going up on one side of a site. How wide is the limited access zone on the unscaffolded side?

The height plus 4 feet, which is 24 feet.

5. Why not fill in the base of a veneer wall with mortar?

That can block the weep holes, and water behind the brick then has no way out.

Key Takeaways

• A standard CMU is nominally 8 x 8 x 16 and actually 7-5/8 x 7-5/8 x 15-5/8 inches.
• The standard mortar joint is 3/8 inch.
• Type S mortar for load-bearing walls is commonly 1 cement, 1/2 lime, 4-1/2 sand.
• Tool joints at thumbprint hardness to compress the mortar.
• Keep weep holes open, with no more than 33 inches between them.
• Set up the limited access zone first, and brace walls over 8 feet.