A waler is a horizontal beam used in construction to brace vertical supports and distribute lateral pressure evenly across a structure. You’ll find walers in two main settings: holding concrete formwork together during a pour, and bracing the walls of trenches and excavations to prevent collapse. In both cases, the waler’s job is the same: absorb sideways force and spread it across a wider area so nothing bulges, buckles, or caves in.
How Walers Work in Concrete Formwork
When concrete is poured into forms, the wet mix pushes outward with enormous pressure. A tall wall form can experience lateral pressure exceeding 2,000 pounds per square foot depending on pour rate and concrete temperature. Without something to resist that force, the vertical form panels would bow outward, creating uneven wall thickness or a dangerous blowout.
Walers run horizontally across the outside of the form panels, tying the vertical supports (called strongbacks or soldiers) together. They’re typically installed in pairs, known as double wales, with snap ties or bolts threaded between them to clamp the two sides of the form together. The spacing between double wales is precise: 5/8 to 3/4 inch apart when using snap ties. Too much gap between the pair can crush the wood or bend the hardware, letting the form bulge and trapping tie components inside the hardened concrete.
Walers are installed from the top of the panel down to the bottom, tightened progressively as they go. Their vertical spacing along the form depends on the pressure the wet concrete will exert, which engineers calculate based on the weight of the concrete (150 pounds per cubic foot for normal weight), the height of the pour, the rate of placement, and the temperature. Faster pours and colder temperatures both increase pressure because the concrete lower in the form stays fluid longer.
Walers in Trench Shoring and Excavation
The other major use for walers is underground. In trench and excavation shoring, walers run horizontally along the trench walls, pressing against vertical planks (called uprights or sheeting) that line the soil face. Cross braces, often hydraulic cylinders, span the width of the trench and push against the walers on each side, holding everything in place against the lateral earth pressure trying to collapse the trench inward.
OSHA’s timber shoring standards for trenches up to 20 feet deep specify waler sizes and spacing based on soil type, trench width, and depth. In firm Type A soil, 8×8 timber wales spaced at four feet vertically can be adequate. In softer Type B or Type C soils, larger members like 10×12 or 12×12 timbers are required, typically spaced at five feet vertically. The standard also requires that wales be installed with their greater dimension horizontal to maximize bending resistance.
A special case worth knowing: when a waler is installed at the very bottom of a trench wall, at the toe where the soil meets the trench floor, it’s called a mudsill. Mudsills serve the same bracing function but anchor the lowest point of the shoring system. OSHA requires that the distance from the center of the lowest cross brace to the trench bottom not exceed 42 inches when mudsills are used, or 36 inches when uprights are embedded directly into the ground.
Materials Used for Walers
Walers are made from timber, steel, or aluminum depending on the application and the loads involved.
- Timber is the most traditional choice, especially in formwork and smaller excavations. Douglas Fir with a minimum bending strength of 1,500 psi is a common specification. Oak, with a lower bending strength of 850 psi, is also used. For marine applications like bulkheads in salt water, pressure-treated lumber rated for continuous water exposure is required.
- Steel handles the heaviest loads and is standard in deep excavation support systems, where walers work alongside secant pile walls and permanent retaining structures. Steel walers distribute lateral earth pressure across large spans without the deflection limitations of wood.
- Aluminum is common in prefabricated hydraulic shoring systems. Aluminum walers come in standard lengths of 6, 8, and 10 feet (and sometimes longer) with hydraulic cylinders already attached. These systems are lighter and faster to install than timber, making them popular for utility trenches and roadwork where crews need to set up and move quickly.
Hydraulic aluminum shoring systems come in different duty ratings. A standard aluminum waler has a section modulus of about 3.67 cubic inches, while heavy-duty versions reach 14.5 cubic inches, nearly four times the bending capacity.
Waler vs. Stringer vs. Whaler
These terms get mixed up regularly, so here’s the distinction. A waler is specifically a horizontal beam that resists lateral (sideways) pressure, whether from wet concrete or soil. A stringer is also a horizontal beam, but it carries vertical loads. In pier and dock construction, for example, stringers run between pile caps and support the decking above, transferring live loads (foot traffic, equipment) down into the piles. Walers on the same structure would brace the bulkhead or retaining wall holding back earth or water.
You’ll sometimes see “whaler” used interchangeably with “waler,” and in practice many crews treat them as the same word. Technical references and engineering standards consistently use “waler” or “wale beam,” so that’s the more precise term. The spelling “whaler” appears more often in informal or regional usage.
Why Proper Waler Installation Matters
Walers are one of those structural elements that only get attention when they fail. In formwork, a missing or poorly spaced waler lets the form bulge during the pour. That means walls with incorrect thickness, embedded hardware that can’t be removed, and potentially a blowout that sends wet concrete and broken form panels into the work area. In excavation, inadequate wales can lead to trench wall collapse, which remains one of the deadliest hazards in construction.
OSHA’s shoring tables account for variables like soil classification, trench dimensions, and cross brace spacing. But those standard tables have limits. They don’t apply when the trench exceeds 20 feet deep, when heavy equipment is working near the edge, or when vertical loads on cross braces exceed 240 pounds per linear foot. In those situations, a registered engineer designs the shoring system from scratch, selecting waler sizes and spacing based on site-specific conditions rather than general tables.