Vertical & Horizontal Formwork Systems

Vertical & Horizontal Formwork Systems

Quick Answer: Vertical formwork molds walls and columns and fights lateral pressure with ties, walers, strongbacks, and braces. Horizontal formwork molds elevated slabs and beams and fights gravity with sheathing, joists, stringers, shores, and often reshores. Pressure on wall forms rises with pour height, placement rate, and conditions that keep concrete plastic longer (including cooler temperatures). Strip and reshore only per engineer and specifications—never invent times.

Module 27308 (Vertical Formwork) is core to the Foundations and Formwork domain. Horizontal systems (NCCER 27309 awareness) appear because commercial carpenters routinely deck elevated slabs, set pans, and work under flying forms. Together with foundations (27307) and tilt-up (27310), these skills support the assessment’s formwork-heavy items.

Vertical Formwork — Walls and Columns

Wall forms are two faces held a designed thickness apart. Wet concrete behaves like a fluid early after placement and pushes outward on both faces. If ties or bracing are undersized or missing, forms blow out, go out of plumb, or create wavy walls.

Vertical Form Components

Column forms may be job-built plywood boxes, fiber tubes (Sonotube-type), steel clamps with plywood, or modular panel systems. Columns develop high pressure over a short perimeter; clamps, yokes, and ties must match the manufacturer’s or design spacing. Plumb both ways and brace until concrete gains enough strength that the column can stand without the form’s full restraint—again, per spec.

Gang Forms, Slip Forms, and Climbing Forms (Awareness)

• Gang forms: Large prefabricated panel assemblies (often with walkways) lifted by crane as a unit. Efficient for repetitive walls. Require engineered design for lifting inserts, bracing, and pour rates. Inspect crane connections and never exceed panel weight ratings.
• Slip forms: Continuously moving forms advanced as concrete is placed for tall structures (silos, cores). Specialized crews and continuous operations—journey carpenters need conceptual awareness, not improvised slip-form setups.
• Climbing / jump forms: Forms that raise in stages (self-climbing hydraulic or crane-jumped) for high-rise cores and shear walls. Sequencing, anchors, and engineering control these systems.

Exam angle: Know that gang forms are large crane-set assemblies for productivity; slip and climbing systems are specialized multi-story methods—not the same as simple hand-set foundation panels.

Concrete Pressure on Forms — Why Forms Fail

Lateral pressure on vertical forms is not a mystery number you invent on the test; you need the factors:

1. Height of plastic concrete — Deeper liquid head → higher pressure at the bottom.
2. Rate of pour (placement rate) — Fast placement stacks fluid concrete before lower layers stiffen → higher pressure.
3. Temperature / mix / admixtures — Cooler concrete and retarders keep the mass fluid longer, so pressure stays high; hot weather and accelerators may reduce the duration of full fluid pressure (design still governs).
4. Vibration — Internal vibration temporarily fluidizes concrete and can increase pressure if overdone or if forms are marginal.
5. Mix density and chemistry — Heavier mixes and some SCMs/admixtures affect pressure; follow formwork design assumptions.

Why forms fail in the field:

• Missing, under-spaced, or failed ties
• Inadequate walers/strongbacks or broken lumber
• Braces removed too early or never installed
• Pour rate exceeding the form design rate
• Forms out of plumb so pressure has a worse lever arm
• Damaged gang-form hardware or reused ties beyond capacity

If pressure exceeds capacity, expect blowouts, bulges, loss of plumb, and catastrophic panel kick-out—all are crush/struck-by events. The carpenter’s controls are: build to the formwork drawing, respect pour-rate limits, watch for leaks and movement during placement, and stop the pour if forms move.

Horizontal Formwork — Elevated Slabs and Beams

Horizontal formwork creates the deck for elevated concrete floors and roofs.

Load path (typical stick-built deck): slab load → sheathing → joists → stringers → shores (posts) → mudsills or lower slab. Every link must be tight, plumb, and on a firm base. Laced bracing and U-heads or screw jacks adjust elevation. Commercial aluminum modular systems replace wood joists/stringers but obey the same load-path idea.

Shoring and Reshoring

• Shores support the formwork and fresh concrete until the slab can carry itself.
• Reshores (or backshores) are posts reinstalled or left under a stripped slab to carry construction loads into lower levels while upper levels are still weak.

Why reshoring matters: Stripping forms early for schedule is common, but a green slab cannot yet take the next floor’s shoring loads alone. Without a reshore plan, lower floors deflect, crack, or collapse. The engineer or formwork designer sets strip times, reshore layouts, and how many floors remain supported. Carpenters execute the plan—they do not freestyle shore removal because “it looked hard enough.”

Flying forms speed repetitive floor plates but demand clear crane paths, level landing, locked legs, and perimeter fall protection. Never ride a flying form as a personnel platform unless it is specifically designed and approved for that use.

Safe Stripping Practice

General principles (project documents always win):

1. Confirm minimum strength or minimum time from the spec/engineer before any strip.
2. Remove formwork in a sequence that does not shock-load remaining supports.
3. Leave reshores as required; do not pull an entire floor of posts in one pass contrary to the plan.
4. Pry carefully—protect concrete edges and architectural faces.
5. Clean, oil, and stack reusable panels; inspect ties and hardware for next use.
6. Maintain fall protection when stripping elevated decks and wall forms.

Do not invent strip times such as “always 24 hours” or “always 7 days” as universal truth. Temperature, cement type, strength requirements for multi-story construction, and post-tensioning schedules all change the answer.

Safety: Crush, Struck-By, and Collapse

Formwork is temporary structure under full design load only for a short window—and failures are often sudden.

• Stay out from under live pours and inadequately braced panels.
• Keep clear of crane-set gang forms and flying tables during lift and set.
• Use tag lines, certified rigging, and exclusion zones.
• Cap or guard rebar; cover formwork floor openings.
• Treat formwork dismantling as a controlled operation—loose panels are heavy and awkward.

Scenario: During a wall pour, a waler starts to bow and a tie starts to neck. Correct response is to stop placement, notify supervision, and reinforce or rebuild—not to “finish the truck” and hope. That judgment is journey-level formwork literacy.

Connecting vertical pressure control, horizontal shore/reshore discipline, and specialized system awareness (gang, slip, climbing, flying, pans) covers Modules 27308 and 27309 concepts tested under Foundations and Formwork on the Commercial Carpenter assessment.