Masonry construction field guide: brick, block (CMU), and stone

What masonry construction is

Masonry construction is the trade of laying units, clay brick, concrete block (CMU), and stone, in mortar to build a wall. The units carry compression well and last for decades. The mortar bonds them, levels them, and seals the joints. That much is old and settled. The part that separates a wall that performs from one that fails is not the laying. It is the water.

A masonry wall is not waterproof, and any mason who tells a builder otherwise is setting up a callback. Brick, block, and stone all absorb water, and mortar joints pass it. Wind-driven rain gets through the face of a masonry wall every storm. The wall does not work by stopping that water. It works by collecting the water behind the face and draining it back out, which is what the flashing and the weeps are for. Everything else, the mortar choice, the reinforcement, the ties, the movement joints, holds the wall up and controls where it cracks.

This guide covers the materials, the wall systems, and the details that decide performance. Masonry bears on a footing or foundation, which is its own design problem covered in the foundation and footings guide, and it cracks unless you let it move, which is covered in the building movement joint guide. Both cross this one constantly.

Is masonry waterproof?

No. Masonry is not waterproof, and the wall is designed around that fact rather than against it. This is the single thing that decides whether a wall leaks, and it is the thing most often missed by people who think a thicker wall is a drier wall.

Water gets into a masonry wall three ways: straight through the units and joints by absorption and capillary action, through hairline separations at the unit-to-mortar bond, and around penetrations and terminations. You cannot seal all of that, and sealers on the face often make it worse by trapping the water that does get in. So the modern masonry wall is a drainage system. It expects water behind the face and gives that water a clear path down to flashing and back out through weeps before it reaches anything that matters.

Frame every detail this way. The flashing is a collector. The weep is the drain. The air space or drainage cavity is the path between them. The water-resistive barrier on the backup is the last line that keeps water off the structure. Miss any one piece and the system fails at the weakest point, which is almost always the base of the wall, a sill, or a shelf angle. Build the wall to drain and it stays dry. Build it to block and it leaks the first hard, wind-driven rain.

The materials: clay brick, concrete block, and stone

Three unit families cover most of the work, and they behave differently enough that you cannot treat them as interchangeable. Clay brick is fired clay, dimensionally small, and it expands slowly and permanently over its life as it reabsorbs moisture after firing. Concrete block, the CMU, is molded concrete, larger and hollow, and it shrinks as it cures and dries. Stone is natural and variable, laid as veneer or as solid units, and its strength and absorption depend on the type.

The other split that matters on every job is structural versus veneer. A structural masonry wall carries load: the floor, the roof, the wall above it. A veneer carries only itself and hands its lateral load back to a backup through ties. CMU is the common structural unit in commercial work, often reinforced and grouted. Brick today is usually a veneer over a stud or CMU backup, though brick was the structural wall for a century and still is in restoration and load-bearing designs. Know which one you are building before you pick the unit, the mortar, and the reinforcement, because the answer changes all three.

Match the unit to the exposure too. A brick rated for severe weathering belongs on a freeze-thaw exposure where a lower-rated unit will spall. The unit standards (ASTM C90 for load-bearing CMU, ASTM C216 for facing brick, C62 for building brick, C652 for hollow brick) set the grades, and the project specification and the engineer call out which grade the wall needs.

What mortar type should I use?

Mortar comes in four common types under ASTM C270, named by decreasing strength: M, S, N, and O. Type M is the strongest at roughly 2500 psi, Type S about 1800 psi, Type N about 750 psi, and Type O about 350 psi. The mnemonic masons carry is the word MASONWORK, whose every other letter spells M, S, N, O. Strongest to weakest, that is the order.

The mistake is reaching for the strongest by default. The right type is matched to the application, and most above-grade exterior masonry is built with Type N, not Type M. Type N is the general-purpose exterior mortar for walls above grade. Type S adds bond and lateral strength and shows up at or below grade and where the wall sees more flexure, like foundation walls and some structural veneer. Type M is the high-compression mortar for below-grade work, retaining walls, and masonry in contact with earth. Type O is a low-strength interior and repointing mortar, and it is the right answer for soft or historic brick where a hard mortar would do damage.

These are starting points, not a rule. The mortar type, the reinforcement, and the wall design are matters for the engineer and the project specification on any structural or engineered masonry, and TMS 402 and TMS 602 with the adopted code edition control the call. Verify the specified type before you batch the first board, because a mortar swapped on the fly is a swap nobody recorded.

Matching the mortar to the unit

The mortar should be weaker than the unit it bonds. That sounds backward to anyone who thinks stronger is safer, and it is the single most expensive misunderstanding in the trade. When a wall moves, and every wall moves, something has to give. If the mortar is softer than the brick, the small cracking and the stress relief happen in the joint, where you can rake it out and repoint it. If the mortar is harder than the brick, the brick gives instead. The face spalls, the units crack, and you cannot repoint a spalled brick.

This rule governs restoration above all. Old brick was soft, low-fired, and laid in soft lime mortar that flexed with the building and breathed. Repoint that wall with a hard portland mortar and you trap moisture, concentrate stress at the face, and pop the faces off the historic brick within a few freeze-thaw cycles. The repair destroys the wall. The National Park Service preservation guidance on repointing historic masonry is built around this exact failure, and it is worth reading before any restoration bid.

So the matching is a real skill, not a catalog pick. Soft unit, soft mortar. Hard new brick, a stronger mortar within reason. On historic and structural work the mortar formulation belongs to the engineer or the preservation spec, and a mortar analysis of the original is the honest way to match it. Get this wrong and you have built cracking into the wall on day one.

The wall systems: single-wythe, cavity, and veneer

A wythe is one unit thickness of wall. How many wythes you have and what sits between them defines the system, and each system manages water differently. Three cover most work.

A single-wythe wall is one unit thick, usually CMU, and it has no cavity behind the face to drain into. It relies on the unit, integral water repellents in the mix and mortar, and careful detailing to control water, because there is no drainage gap as a backup. It is economical and common on warehouses and utility walls, and it is the least forgiving of bad flashing.

A cavity wall is two wythes with a deliberate air space between them, and that air space is a drainage gap. Water that crosses the outer wythe runs down the back of the face, hits flashing at the base of the cavity, and exits through weeps. This is the water-managed wall in its clearest form. A veneer is a non-structural outer skin, brick or stone, anchored back to a separate backup of wood stud, steel stud, or CMU, with a drainage cavity behind it. The veneer carries only its own weight and passes wind load to the backup through ties. Most new brick is built this way.

The cavity drainage wall

A cavity wall earns its keep through the gap, so keep the gap clear. The air space behind the outer wythe is the drainage path, commonly held to a minimum around 1 in clear and often built at 2 in to give mortar droppings somewhere to fall without bridging the cavity. The moment mortar squeezings pile up on the flashing and bridge that gap, water walks across the bridge to the backup and the wall leaks, even though every other piece was right.

The backup carries the second half of the system. A water-resistive barrier goes on the face of the backup so that any water reaching the back of the cavity sheds down the barrier instead of soaking into the sheathing or the block. At the bottom of the cavity, and at every interruption like a shelf angle or a window head, flashing collects the water and weeps let it out. That base detail is the most-inspected and most-failed point in the whole wall.

Keep the cavity clean as you lay up. Bevel the mortar bed slightly toward the cavity so squeezings fall clean, use a cavity drainage mat or mortar collection device above the flashing to keep the weeps open, and protect the flashing as the wall goes up. The wall design, the cavity width, and the tie spacing are engineered and governed by TMS 402, so build it to the drawings and confirm the dimensions against the spec.

Brick and stone veneer over a backup

Anchored veneer is a thin outer skin that looks structural and is not. The brick or stone you see carries its own dead weight down to a foundation or a shelf angle, and nothing else. Every bit of wind load on that face goes back to the structural backup through the ties. Treat the veneer as a rain screen with a drainage cavity behind it, not as a wall in its own right.

The backup does the structural work and holds the barrier. Over wood or steel stud, the sheathing carries an air and water barrier, and the ties screw through to the studs. Over CMU, the block is the backup and the barrier goes on its face. Either way the cavity behind the veneer drains, the ties tie it back, and the flashing and weeps at the base let the water out. The veneer is the sacrificial, replaceable, water-shedding face. The drainage and the barrier behind it are what actually keep the building dry.

The two failures that show up years later are both invisible at handover. Ties left out, spaced too far, or never fastened to the framing, so the veneer has nothing holding it in a windstorm. And a cavity packed with mortar droppings that bridge the flashing and pipe water into the backup. Anchored veneer is governed by the veneer provisions of TMS 402, and the tie type, spacing, and corrosion protection come off the engineered drawings.

Reinforcing masonry: rebar, bond beams, and joint reinforcement

Masonry is strong in compression and weak in tension, so reinforced masonry puts steel where the tension is. There are three kinds and they do different jobs. Vertical rebar sits in CMU cells that are then grouted solid, carrying flexural and out-of-plane load and tying the wall to the footing through dowels. Bond beams are horizontal courses of channel-shaped block filled with rebar and grout, running as a continuous reinforced band at floors, at the top of the wall, over openings, and at intervals up the wall. Joint reinforcement is light wire, ladder or truss shaped, laid in the bed joints to control shrinkage cracking and tie multi-wythe walls together.

Do not confuse the three or substitute one for another. Joint reinforcement wire is not a structural replacement for bond-beam rebar, and a bond beam is not a substitute for the vertical steel the engineer placed for flexure. Each is sized and located on the structural drawings. The rebar size, the cell spacing, the bond-beam locations, and the joint-reinforcement spacing are engineered values, and on any structural masonry they belong to the engineer and TMS 402, not to field judgment.

The field failure here is quiet and serious. Rebar left out of cells, dowels missed at the footing, lap splices too short, or steel that drifted to the side of the cell so the grout cannot surround it. None of that shows once the wall is grouted and faced. That is exactly why grouted, reinforced masonry gets special inspection. Verify the steel is placed, spaced, lapped, and positioned before the grout goes in, because after grouting the only record is the inspection you did or did not do.

Grouting the reinforced cells

Grout is a fluid, high-slump concrete that fills the reinforced cells of CMU and bonds to the rebar and the block so the wall acts as one reinforced unit. It is not mortar and it is not structural concrete. It is mixed wet, with a slump commonly in the 8 in to 11 in range, on purpose, so it flows into the cell and surrounds the steel completely. Grout that is too stiff leaves voids around the bar, and a voided cell is a cell that does not carry the load the engineer counted on.

Two methods cover the work. Low-lift grouting builds the wall in shorter pours, commonly to about 5 ft 4 in, and grouts each as you go. High-lift grouting lays the wall full story height, up toward 24 ft under the code limits, then grouts in lifts with cleanout openings at the base so you can clear droppings and confirm the steel before the pour. High-lift needs cleanouts and a clean cell. Skip them and you cannot see or fix what is at the bottom.

Consolidation is the step that makes or breaks the pour. Grout placed in lifts over 12 in must be consolidated with a mechanical vibrator, the stinger pushed to the bottom of the lift and drawn out slowly, then reconsolidated after initial water loss to close the settlement gaps. Lifts of 12 in or less can be puddled with a rod. Grout slump, lift height, and consolidation are specified in TMS 602, so follow the spec and the special inspector on the consolidation method.

Bond pattern, coursing, and the mason's layout

Bond is how the units overlap, and it is both structural and visual. Running bond, each unit offset half a unit from the course below, is the standard structural pattern because the overlap distributes load and ties the wall together along its length. Stack bond, units aligned in vertical columns with no overlap, has little inherent strength along the wall and needs extra joint reinforcement to hold together, so it is an engineered and reinforced choice, not a default.

Coursing is the vertical math: the unit height plus the bed joint, repeated, has to land on the floor lines, the window heads, and the wall top without a sliver course or a fat joint. A mason lays out the coursing dry, sets a story pole, and works to it, because the layout decided at the base controls how the whole wall reads three stories up. The standard bed and head joint is 3/8 in, and holding it consistent is what keeps the coursing true and the joints weather-tight.

Level, plumb, and line are the craft. The wall goes up to a taut line, the corners (the leads) are built first and checked plumb, and the field is filled between them. A wall that is out of plumb or off-coursing is not just ugly. It throws off the flashing laps, the shelf-angle bearing, and the window openings that come after, and every trade behind the mason inherits the error.

Where does a masonry wall leak? The flashing

A masonry wall leaks where the water it collected has nowhere to go, and that is wherever the flashing is missing, lapped wrong, or has no end dam. Flashing is the collector in the drainage system. It is a continuous water-stop built into the wall that catches the water draining down the cavity or the back of the face and directs it out through the weeps. Put it at the base of the wall, at every sill, at every window and door head, and on top of every shelf angle and relieving angle.

Through-wall flashing runs from the cavity, across, and out to the face or just behind it, so the water it catches has only one way to go, which is out. The details that get skipped are the ones that cause the leaks. The flashing has to turn up the backup to form a back dam so water cannot run behind it. It has to be lapped and sealed at splices so a seam does not become a funnel. And it has to be closed at the ends of each run with an end dam, a turned-up corner that stops the collected water from running off the end of the flashing into the wall instead of out the weeps above it.

Where the flashing dies into nothing is where the wall stains and rots from the inside. Flashing material, laps, terminations, and locations are detailed on the drawings, and the water-management requirements tie back to TMS 402 and TMS 602 and the project spec. The blunt version: no flashing, no drainage, and a masonry wall with no drainage is a wall that holds water against the building.

Why do brick walls have weep holes?

Weep holes are the exit. A brick wall has them because the wall collects water behind the face on the flashing, and that water has to drain back out or it backs up, saturates the wall, and finds its way inside. The weep is the open path at the flashing line that lets the collected water out. Cover the weeps or leave them out and the flashing becomes a bathtub.

Weeps go in the head joints of the first course directly above each line of flashing: at the base of the wall, above shelf angles, and above window and door heads. Common forms are open head joints, joints left mortar-free, or vents and rope wicks set in the joint. Spacing comes off the spec, with open head joints commonly held around 24 in on center and weep tubes or wicks closer. Keep the weep at or just above the flashing so the water it drains actually sits on the flashing, not above a dead pocket.

Blocked weeps are one of the most common defects a mason creates and the easiest to prevent. Mortar droppings fall down the cavity, pile on the flashing, and plug the weeps from behind. A mortar collection device or drainage mat above the flashing keeps the droppings off the weeps. Weep size and spacing follow TMS 602 and the project spec, but the rule never changes: water that gets in has to get out, and the weep is the only door.

Ties and anchorage

Ties are what hold a veneer to its backup, and a veneer with bad ties is a wall waiting for a windstorm. The veneer carries no lateral load on its own. Every pound of wind on that face transfers back to the structure through the ties, so the tie type, the spacing, the embedment, and the corrosion protection are all load-path decisions, not hardware afterthoughts.

Spacing and embedment come off the engineered drawings, but the field targets are worth carrying. Adjustable veneer anchors are commonly spaced about one tie per 2.67 sq ft of wall, which works out near 16 in on center each way, tightened up around openings, at movement joints, and at the top of the wall. The wire embeds at least about 1 1/2 in into the veneer bed joint with roughly 5/8 in of mortar cover to the face, and the bed joint has to be thick enough to bury it. On a stud backup the anchor fastens through the sheathing into the framing, not just into the sheathing.

Corrosion is the slow failure. A tie that rusts away leaves the veneer unsupported decades after everyone has forgotten the wall, so ties are hot-dip galvanized or stainless (Type 304 or 316) per the exposure. Joint reinforcement that doubles as a tie has the same corrosion requirement. The anchorage provisions live in TMS 402, and the engineer sets the type and spacing for the wind load and the backup, so confirm both before you start the veneer.

What is the difference between a control joint and an expansion joint in masonry?

A control joint is for CMU because concrete block shrinks, and an expansion joint is for clay brick because brick grows. Same idea, opposite directions, and using the wrong one is a real failure. Concrete masonry shrinks as it cures, dries, and carbonates, so a control joint is a planned weak line that opens as the block pulls away from it, sending the shrinkage crack to the joint instead of through the wall. Clay brick expands permanently after firing as it reabsorbs moisture, plus thermal movement on top, so an expansion joint is a compressible gap that closes as the brick grows, giving the expansion somewhere to go before it crushes the wall against a corner or a frame.

The detail follows the direction of movement. A brick expansion joint stays open and compressible, filled with a backer rod and sealant over a compressible filler, and it never gets mortar, because mortar in the joint defeats it and the expanding brick will spall at that point. A CMU control joint can take mortar or a sealed joint over a gasket, since the block is moving away from the joint, not into it. In a modern cavity wall the brick veneer and the CMU backup move on their own schedules, so their joints are located independently, one for the growing brick face, one for the shrinking block behind it.

Spacing and location are engineered, and this is where the masonry guide hands off to the movement joint guide, which covers sizing the gap, running it continuously through every layer, and keeping it watertight. The short version: leave the joints out, or block them with mortar, and the wall cracks itself apart relieving a movement you refused to plan for. Joint type, spacing, and width come from the engineer and TMS 402, so build them where the drawings show them.

Lintels and bearing over openings

Every opening in a masonry wall needs a lintel to carry the masonry above it across the gap, and the lintel needs real bearing on each side. Three kinds are common. A loose steel angle, the trade calls it a loose lintel, carries brick veneer over windows and doors. A precast concrete lintel drops in over openings in block walls. And a masonry lintel, a course of bond-beam or lintel block reinforced and grouted, carries the load as part of the wall itself in reinforced CMU.

Bearing is the part that gets shorted. The lintel has to sit on solid masonry far enough each side to spread its reaction without crushing the units under it, commonly at least about 4 in to 8 in of bearing per end depending on the span and the load. Too little bearing and the corner of the opening cracks and the lintel sags. The load path has to land somewhere it can be carried down to the footing, so the masonry under the bearing has to be solid, sometimes grouted, not a hollow cell.

Deflection matters because masonry is brittle. A steel lintel that deflects too much under the brick above it cracks the masonry it carries, so lintels supporting masonry are held to a tighter deflection limit than ordinary steel, commonly around span over 600. And the loose steel lintel in a drainage wall needs flashing and weeps over it like any other shelf, because it is one more ledge where water collects. Lintel size, bearing, and deflection are structural, set by the engineer and the project documents, so size them off the drawings.

Cold-weather and hot-weather masonry

Weather changes how mortar and grout set, and both ends of the thermometer have their own rules. The line for cold weather is about 40°F. Below it the trade follows cold-weather provisions, because if the water in fresh mortar freezes before it sets, the ice expands, ruptures the paste, and you get a mortar that crumbles and never bonds. The protections are practical: heat the mixing water and sometimes the sand, do not lay on frozen units or a frozen foundation, and keep the laid wall above freezing after placement, commonly held above 32°F for about 24 hours for ungrouted work and 48 hours for grouted work. Never lay frozen, snow-covered, or ice-glazed units.

Hot weather is the opposite problem. Above roughly 100°F, or 90°F with an 8 mph wind, the mortar stiffens fast as the heat and the dry units pull the water out of it, and a mortar that loses its water before it bonds gives a weak joint. The fix is retempering, adding water and remixing to restore workability, which is allowed up to about two hours from mixing and not after. Past two hours the mortar is discarded, not stretched. In heat you also wet-down highly absorptive brick so the unit does not suck the water out of the mortar before it bonds, the property the trade calls initial rate of absorption, or suction.

Suction is the under-appreciated variable in any weather. A dry, thirsty brick robs the mortar of the water it needs to cure and you get a weak, poorly bonded joint that leaks. A soaking-wet brick floats on the mortar and the wall slumps. The target is a damp unit with the surface dry. Cold and hot weather requirements are spelled out in TMS 602 and the project cold-weather and hot-weather plans, which are often required submittals, so have the plan before the temperature forces the call.

Efflorescence: the white bloom

Efflorescence is the white, powdery salt deposit that shows up on the face of new masonry, and it is a symptom, not a stain to argue about. It needs three things at once: soluble salts in the masonry materials, water to dissolve them, and a path for that water to migrate to the surface and evaporate, leaving the salt behind. Take away any one of the three and the bloom stops. That is the whole story, and it tells you the cure.

New-building bloom is common in the first months as the wall dries out and the construction water carries its salts to the surface. It usually brushes and rinses off and does not come back once the wall has dried, so do not panic over the first appearance. Recurring efflorescence is the one to chase, because it means water is still getting into the wall and moving through it, which points at a flashing, weep, coping, or sealant failure. The white bloom on a two-year-old wall is the wall telling you it is wet inside.

Prevention is the same set of details that keep the wall dry. Keep materials covered and off the ground so they do not soak up salts and water before they go in the wall, cover the wall at the end of each day so it does not fill with rain, use low-alkali materials where specified, and detail the flashing, weeps, and coping so the wall drains. Light efflorescence cleans with dry brushing and water, sometimes a proprietary cleaner. If it keeps coming back, fix the leak, not the stain.

Cleaning new masonry

New masonry gets cleaned to remove mortar smears, and this is where a careless crew does damage that nobody can undo. The default reach for muriatic acid straight out of the jug is exactly the wrong move. Strong or improperly used acid burns the mortar joints, etches the units, and pulls metals out of the brick that show up as green vanadium staining or brown manganese staining, plus the white scum acid leaves when it reacts with fresh mortar. The cleaning becomes a worse problem than the smears.

The method that works is patient. Let the mortar cure first, commonly at least about 7 days, so the joints are hard enough to take cleaning. Knock off the big chunks dry with a wood paddle, never a metal tool that scratches. Saturate the wall with clean water first so the cleaner sits on the surface instead of soaking into dry brick. Use a proprietary masonry cleaner mixed to the label, or a properly diluted acid only where the brick manufacturer allows it, work a small area, and rinse heavily before it dries. Do not clean below about 40°F, and follow the brick maker's cleaning guidance, because some brick are damaged by acid no matter how you dilute it.

Test a small, hidden area first, always. Brick from different runs and colors react differently to the same cleaner, and a panel that looked fine on one elevation can stain on another. The finish you hand over is the one the owner sees for thirty years, so clean it the slow, tested way rather than the fast way that burns it.

Masonry bears on the footing

A masonry wall is heavy, and every course of it lands on a footing or foundation that has to carry the load into the soil. The footing is its own design problem, sized to the wall load and the soil bearing, and it is covered in full in the foundation and footings guide. The handoff between the two is where the mason has to get it right, because the wall is only as good as what it stands on.

Three things matter at the base for the mason. The footing has to be level and at the right elevation so the first course starts on coursing and the wall lands true at the top. The vertical reinforcement that runs up the wall has to be tied to dowels left in the footing, lapped to the length the engineer specified, or the wall is not connected to its base. And the base of the wall is the first and most critical flashing line, because it is the lowest collector in the whole drainage system and the place water ends up.

Build the wall off a footing that is out of level or short on dowels and you have a problem that compounds upward. Confirm the footing elevation, the dowel placement, and the base flashing before the first course, because all three get buried fast and none of them can be fixed from above once the wall is up.

QC, special inspection, and the prism test

Engineered masonry gets inspected because most of what makes it work disappears behind the face. The mortar, the grout, the reinforcement, the ties, and the flashing are all covered up as the wall goes up, so the inspection is the only durable record that they were right. On structural masonry, the code requires special inspection: a third-party inspector verifying the materials, the reinforcement placement, the grout, and the construction against the approved drawings as the work proceeds.

The inspector watches the things you cannot see later. That the rebar is the right size, in the right cells, lapped long enough, and positioned so grout surrounds it. That the cells are clean and the cleanouts are open before a high-lift pour. That the grout is consolidated and reconsolidated. That the mortar joints are full and tooled. That the ties are present, spaced, and fastened to the backup. And that the flashing and weeps are built before the courses above cover them.

Strength gets verified two ways under TMS 602. The unit-strength method establishes the wall's design strength, f-prime-m, from the documented strength of the units and the mortar type, with no wall testing. The prism test method builds small wall assemblies and tests them in compression per ASTM C1314 to confirm f-prime-m directly. Mortar and grout get their own tests, with grout sampled per ASTM C1019. The level of inspection and which verification method applies are set by the engineer, the code, and the AHJ, so confirm the inspection scope before the wall starts.

What to document

Masonry hides its own evidence, so the record is the wall's history once the face is up. The unit, the mortar type and the batch, the grout, the reinforcement placement, the tie spacing, the flashing, and the inspections all vanish behind the brick within hours. Write them down as you build, because the day a wall cracks or leaks, the question is what went into it, and a wall that was photographed and logged answers that question in minutes instead of demolition.

Capture the units and grades, the mortar type and any mix or admixture changes, the grout mix and slump, the rebar size and placement with the cells grouted, the bond-beam locations, the tie type and spacing, the flashing material and the weep locations, the movement-joint locations, the weather and any cold or hot weather protection used, and each special-inspection sign-off with photos before cover. A field tool like FieldOS makes this stick: photograph the reinforcement and flashing before the grout and the courses cover them, tag it to the wall and the elevation, and the record is built as the wall is, not reconstructed from memory later.

Common failures and how they show up

Most masonry callbacks come from a short list, and they all share a tell: the wall looked fine at handover. No flashing or weeps, or weeps blocked by mortar droppings, so the wall collects water and cannot drain it, and it leaks at the base, the sills, and the shelf angles in the first hard rain. Mortar stronger than the unit, so the wall spalls and cracks the brick faces instead of the joints when it moves, which is the failure that ruins restoration work. Missing reinforcement, dowels, or ties, none of it visible once the wall is grouted and faced, until the wall flexes or a windstorm finds the veneer with nothing holding it.

The other two are about movement and weather. No movement joints, or joints filled with mortar, so the wall cracks itself relieving the expansion or shrinkage it was never allowed to release, with the cracks running through the units at the corners and openings. And mortar frozen before it set, which crumbles and never bonds, leaving a joint that looks laid but holds nothing. Every one of these is cheaper to prevent on the way up than to chase from the inside after the owner finds the stain.

Field checklist

Common mistakes

• No flashing or weeps, so the wall collects water and has no way to drain it back out.
• Mortar stronger than the unit, which cracks and spalls the brick instead of the joint when the wall moves.
• Missing reinforcement, dowels, or wall ties, none of which is visible once the wall is grouted and faced.
• No movement joints, or joints filled with mortar, so the wall cracks relieving expansion or shrinkage.
• Weep holes blocked by mortar droppings piled on the flashing, which turns the flashing into a bathtub.
• Laying in freezing weather and letting the mortar freeze before it sets, leaving a joint that never bonds.
• Cleaning new masonry with strong acid on a dry wall, burning the joints and staining the units.

Standards and references

The masonry code is TMS 402, Building Code Requirements for Masonry Structures, paired with TMS 602, the Specification for Masonry Structures. TMS 402 sets the design rules, the reinforcement and the anchorage provisions, the veneer requirements, and the water-management framework. TMS 602 covers the construction: the mortar and grout, the placement and consolidation, the cold and hot weather provisions, and the inspection and strength verification. Both are adopted through the building code, so the edition the jurisdiction has adopted, with local amendments, controls.

The material standards are ASTM. Mortar is ASTM C270, which defines types M, S, N, and O. Grout is ASTM C476, with grout strength sampled per ASTM C1019. Units are ASTM C90 for load-bearing CMU, C216 for facing brick, C62 for building brick, and C652 for hollow brick. Prism testing for f-prime-m follows ASTM C1314, and reinforcing steel is typically ASTM A615. Cite the standard that governs the point and confirm the current designation, because ASTM and TMS both revise on a cycle.

For structural and engineered masonry, the mortar type, the reinforcement, the grouting, the ties, and the flashing are the engineer's call and the project specification's, hedged to TMS 402 and TMS 602 and the AHJ. For historic and restoration work, match the original mortar and follow the preservation guidance, because the new-construction rules can do real damage to a soft, old wall. When the spec and the field disagree, the documents and the engineer settle it, not the habit.

Units and terms

Masonry carries its own vocabulary, and the same wall reads differently across a drawing set, a submittal, and a spec. The terms below are the ones that decide whether a wall is built the way it was drawn.

Masonry is units laid in mortar. CMU is concrete masonry unit, the concrete block. Mortar types run M, S, N, and O by decreasing strength. A wythe is one unit thickness of wall. A cavity wall has two wythes with a drained air space between them, while a veneer is a non-structural outer skin anchored to a separate backup. A bond beam is a horizontal reinforced and grouted course. Through-wall flashing is the water-stop that collects water and directs it out. A weep hole is the opening at the flashing that drains that water. A wall tie anchors a veneer to its backup. A control joint relieves shrinkage in CMU; an expansion joint relieves growth in brick.

Masonry / CMU

Units laid in mortar; CMU is the concrete masonry unit, the concrete block

Mortar types M, S, N, O

ASTM C270 types by decreasing strength; match to the unit, not always the strongest

Wythe

One unit thickness of a masonry wall

Cavity wall vs veneer

Cavity wall is two wythes with a drained air space; veneer is a non-structural skin on a separate backup

Bond beam

A horizontal course of reinforced, grouted block running as a continuous band

Through-wall flashing

The continuous water-stop that collects water in the wall and directs it out

Weep hole

The opening at the flashing line that drains the collected water back out

Wall tie

The corrosion-resistant anchor that ties a veneer back to its structural backup

Control vs expansion joint

Control joint relieves CMU shrinkage; expansion joint relieves clay brick growth

Related tools

Calculators and readiness checks for this work

Compare your options

FAQ

People also ask

• What is a footing?
• What is a building expansion joint?
• What is the difference between mortar and grout in a block wall?
• Why do bridge decks deteriorate faster than the rest of the bridge?
• How is a commercial concrete pool built?