11.7 Masonry Reinforcement, Grouting & Wall Systems
Key Takeaways
- Grout is a fluid mixture placed to bond reinforcement to masonry units; it is proportioned for high slump (8 to 11 inches) and is not the same material as mortar
- Fine grout is used in narrow cells and thin joints; coarse grout containing pea gravel is used where the space is large enough to accept it
- High-lift grouting above about 5 feet requires cleanout openings at the base of each grouted cell so debris can be removed and steel inspected
- Bond beams are horizontal grouted courses containing continuous reinforcement, used at floor and roof lines, above openings, and at wall tops
- Hot-weather masonry practice — wetting units where required, shading materials, and protecting fresh work — governs most Arizona placements
Reinforced Masonry Is a Different Trade From Mortar Work
Quick Answer: In reinforced concrete masonry, the block and mortar form a set of vertical cells and horizontal bond beams that are filled with grout around reinforcing steel. Grout is not mortar: it is proportioned to be fluid — commonly an 8 to 11 inch slump — so it flows around bars and fills every void.
Section 11.3 covered units, mortar types, and laying practice. This section covers what turns a stacked wall into a structural element. On the commercial trade exam, masonry questions run heavily toward reinforcement placement, grouting procedure, and inspection — the things a general building contractor supervises rather than performs.
Mortar Versus Grout
| Mortar | Grout | |
|---|---|---|
| Purpose | Bonds units together; fills the joints | Bonds reinforcement to the masonry; fills cells and bond beams |
| Consistency | Stiff, workable, retains its shape on a trowel | Fluid, self-consolidating in placement |
| Slump | ~ 2½ inches (measured by cone penetration in practice) | 8 to 11 inches |
| Aggregate | Sand only | Sand (fine grout) or sand plus pea gravel (coarse grout) |
| Placed by | Mason with a trowel | Pump, bucket, or chute into cells |
Grout is intentionally wet. The high water content that would ruin concrete is correct here, because the dry masonry units absorb excess water from the grout almost immediately, dropping the effective water-cement ratio after placement. A stiff grout that will not flow leaves voids around the steel, which is the failure the inspection process exists to catch.
| Grout type | Use |
|---|---|
| Fine grout | Narrow cells, small clearances, thin collar joints |
| Coarse grout | Larger cells with adequate clear dimension to pass pea gravel |
Choose by the smallest clear dimension the grout must pass through, including around reinforcing bars.
Reinforcement Placement
Vertical steel sits in cells and is held in position by positioners or by tying to dowels projecting from the foundation. Two requirements decide whether it works:
- Position. Bars must be centered in the cell (or at the specified location) and remain there during grouting. A bar leaning against the block face has no grout cover and is not doing what the engineer designed.
- Lap splices. Bars are lapped the specified length, which is stated on the structural drawings and depends on bar size, grout strength, and cover. Field crews should never eyeball a lap.
Horizontal steel comes in two forms:
| Form | Where |
|---|---|
| Joint reinforcement (ladder or truss wire) | Bedded in the mortar joint at specified vertical intervals — commonly every 16 inches |
| Bond beam reinforcement | Continuous bars in a grouted bond-beam course |
Bond beams are horizontal courses formed with bond-beam or lintel block, reinforced and grouted continuously. They appear at floor and roof bearing lines, at the top of walls, above openings, and at intervals set by the structural drawings. They tie the wall together, distribute concentrated loads, and are essential to the wall's out-of-plane and seismic performance. Where a bond beam sits over a cell that is not to be grouted, the bottom is closed off — with metal lath or a plate — so grout stays in the beam rather than running down the wall.
Low-Lift and High-Lift Grouting
The wall cannot be grouted to full height in one pour without either blowing the wall apart or leaving voids. Two procedures exist:
| Low-lift grouting | High-lift grouting | |
|---|---|---|
| Procedure | Lay a limited height of wall, then grout, then continue | Lay the wall to full story height, then grout in lifts |
| Typical lift | Roughly 4 to 5 feet at a time | Grout placed in lifts within a taller pour, consolidated between lifts |
| Cleanouts | Generally not required | Required at the base of every grouted cell |
| Advantage | Simple; no cleanout patching | Faster; fewer interruptions to the masons |
Cleanout openings are the detail the exam tests. When the grout pour height exceeds roughly 5 feet, an opening at least about 3 inches across is left at the bottom of each cell to be grouted. Their purpose is twofold: mortar droppings and debris are removed through them, and the inspector verifies reinforcement position and lap length before the cells are closed and grouted. They are then sealed to resist the grout pressure.
Consolidation. Grout must be consolidated — mechanically vibrated — and then reconsolidated after initial water loss so that the settlement shrinkage does not leave a void at the top of the lift. Skipping reconsolidation is a common source of hollow bond beams.
Hot-Weather Masonry — the Arizona Default
Most Arizona masonry is placed in hot-weather conditions, and the governing concern is that mortar and grout lose water to evaporation and to the units faster than hydration can use it.
| Condition | Practice |
|---|---|
| Rising ambient temperature | Shade sand and mixing water; use cool mixing water |
| High temperature and wind | Reduce the time mortar sits before use; retemper only within the allowed window; work in shorter runs |
| Units hot to the touch | Shade unit stockpiles; do not wet concrete masonry units, which are laid dry — this is opposite to clay brick with high absorption, which may require wetting |
| Fresh work exposed | Fog and cover completed work; protect from direct sun and wind |
That third row is a classic exam discriminator. Clay brick with a high initial rate of absorption may need to be wetted before laying so it does not pull water out of the mortar. Concrete masonry units are laid dry — wetting CMU adds water the unit will later give up as shrinkage, producing cracking.
Warning: in monsoon season the opposite risk appears. Freshly laid masonry must be covered at the end of each day, because a downpour on green work washes out joints and leaches efflorescence-forming salts to the surface.
What distinguishes grout from mortar in reinforced masonry construction?
A mason plans to grout a CMU wall in a single pour approximately 8 feet high. What does the procedure require?
Why is grout reconsolidated after initial placement?
In hot Arizona conditions, how should concrete masonry units and high-absorption clay brick be handled before laying?