Masonry bonding

A brick is sized for one hand: about four pounds, small enough to lay all day. A wall built of them is only as strong as the way they overlap. Bonding is that overlap: the arrangement that keeps vertical joints from lining up, so a load spreads sideways through the wall instead of running down a crack, and that ties the layers of a thick wall into one mass. The pattern the bricks make on the face is a by-product, and over the centuries it became a language of its own.

Wythe

A vertical layer one unit thick. The wall in the figure is two wythes, 8 in nominal.

Course

One horizontal row of units.

Bed joint

The horizontal layer of mortar each course is laid on.

Head joint

The vertical joint between two units in a course.

Collar joint

The vertical joint between two wythes, parallel to the face.

Stretcher

A brick laid flat along the wall, its long side showing.

Header

A brick laid flat across the wall, its end showing. In an 8 in wall it reaches through both wythes.

Closer

A cut brick that finishes a course or keeps the lap at a corner. A queen closer is a brick split lengthwise.

The figure uses the US modular brick. Its actual size is 3⅝ × 2¼ × 7⅝ in (92 × 57 × 194); add a ⅜ in (10) joint and it occupies 4 × 2⅔ × 8 in, its nominal size. Two stretchers side by side with a joint between are exactly as deep as one header is long, which is what lets the two wythes of an 8 in wall be bonded with whole bricks. Three courses make 8 in, so heights work in multiples of 8 in and lengths in multiples of 4 in, and a wall planned to those numbers needs few cut bricks.

Switch the figure between them. Each is the same corner, laid again course by course.

Running

Stretchers only, each course shifted half a brick. With no headers, the two wythes are joined by steel ties in the bed joints. The usual bond for veneers and cavity walls.

Common

Running bond with a full course of headers every sixth or seventh course. Also called American bond. Pick the interval in the figure and light the headers to see the bands.

Flemish

A header and a stretcher alternate in every course, each header centred on the stretcher below. Ends of darker, harder-fired headers were often set into the face to make a pattern.

English

Whole courses of headers alternate with whole courses of stretchers. The stretchers’ joints line up from one stretcher course to the next. Sturdy and plain.

Stack

Every head joint in line. Nothing overlaps, so the wall has no bond of its own: steel joint reinforcement at 16 in (405) on centre holds an unreinforced stack-bond wall together.

Variants refine these: Flemish cross and Flemish diagonal bonds shift the courses to draw crosses and diamonds, and garden-wall bond sets one header to every three stretchers for light boundary walls.

At a corner the two walls take turns: in one course wall A runs through to the outside face, in the next wall B does, so the corner is woven rather than butted. In Flemish and English bond the corner brick is a header, and the bricks have to be shifted a quarter of a length to keep every header over the middle of a stretcher. The mason does this with a queen closer laid right next to the corner header. In Flemish or English bond, light the closers in the figure: there is one in every course at the corner, alternating from face to face.

The free ends of the walls are left toothed, each course stopping at its last whole brick. Toothing is how a wall is left to be continued; the alternative, racking each course back half a brick, is stronger and is how corner leads are usually built.

The wythes of a solid wall must act together or each will buckle on its own. Headers do it with brick: they should make up at least 4% of the face and sit no more than 24 in (610) apart each way. Common bond’s header course every sixth course puts them 16 in apart.

Without headers, steel does it. Ties of 3⁄16 in (5) corrosion-resistant wire are set in the bed joints, one for every 4½ sq ft (0.42 m²) of wall at most, no more than 16 in (405) apart vertically and 36 in (915) horizontally, staggered from course to course and covered by at least ⅝ in (16) of mortar from either face. They are hidden once the wall is built; light them in the figure and they are drawn dashed, as hidden lines are drafted.

So the bond is chosen first by what the wall is. A veneer, one wythe in front of a frame, has nothing to bond to and is laid in running bond with ties; a solid wall bonds its wythes with headers, and the pattern of the headers becomes its face:

Mortar joints run from ¼ to ½ in (6 to 13) and are usually ⅜ in (10). How the joint is finished matters more than it looks. A tooled joint, concave or V-shaped, is pressed in with a jointer, which compacts the mortar against the brick and sheds rain best. Troweled joints are cut off with the trowel; of these the weathered joint, sloped outward, is the one to use outside. A raked joint, scraped back square, casts a strong shadow but holds water on its ledge and belongs indoors.

A brick has three pairs of faces, and a mason names it by the face that shows. Switch the figure to Positions: each brick is set with its exposed face, shaded, on one line, as if in a wall.

Rowlocks cap walls and form sills; soldiers make bands and the flat arches over openings. Sailors and shiners are mostly decorative and need solid bricks: they show the bed face, which on most bricks is cored with holes and never meant to be seen.