A formwork tie rod is a coarse-threaded steel rod that ties the two faces of wall formwork together against the hydrostatic pressure of fresh concrete — at a 4 m pour depth and 25 kN/m³, lateral pressure reaches roughly 80 kPa at the base, so without ties the panels would simply be pushed apart. The mainstream systems are DW15 and Rd16 / Rd20; for watertight structures such as basements and tanks the rod carries a welded water-stopper plate to break the seepage path. This guide covers rod sizing from hydrostatic load, water-stopping and lost-tie systems, removal and patching, and a 12-step installation.
1. What a formwork tie rod is
A formwork tie rod is a steel rod with continuous coarse thread that ties the two faces of a concrete wall formwork together against the hydrostatic pressure of fresh concrete. Without tie rods, the pressure of a fluid concrete column would push the formwork panels apart — at 4 m pour depth and 25 kN/m³ self-weight, the lateral pressure is ~80 kPa at the base. Tie rods make wall casting physically possible.
The rod passes horizontally through both formwork panels and the wall void, terminating in cone nuts on each side that tension against waling beams. The whole system — rod + cones + plate-anchors + waling — is the "tie system." When you specify a tie rod, you're selecting one part of an assembly; the rod is interchangeable but the cones and plates usually come from the formwork manufacturer.
Tie rods are the most-used and least-glamorous accessory in formwork. A medium-size project (apartment block, basement parking, water tank) consumes 5,000–20,000 rods. Pricing is per-metre, lead time is days not weeks, and the cost differential between brands is often the single biggest savings line in a formwork tender.
2. DW15 vs Rd16 vs Rd20 — the thread system decides everything
Tie rod hardware comes in three incompatible thread families. Pick one and stick with it across the whole project — mixing threads is the #1 site error:
| Spec | DW15 (Dywidag) | Rd16 | Rd20 |
|---|---|---|---|
| Root diameter | 15 mm | 14 mm | 17 mm |
| Outer thread diameter | 17 mm | 16 mm | 20 mm |
| Thread pitch | 7.5 mm | 8.0 mm | 10.0 mm |
| Allowable working load | 90 kN | 90 kN | 140 kN |
| Allowable formwork load | 150 kN | 150 kN | 230 kN |
| Steel grade / UTS | ≥ 700 N/mm² | ≥ 800 N/mm² | ≥ 800 N/mm² |
| Used by | Most common formwork systems | Some specialist formwork systems | Heavy-duty / large-section walls |
| Standard length | 0.5 – 6.0 m + custom | 0.5 – 6.0 m | 0.5 – 6.0 m |
3. Anatomy — rod, cone, plate-anchor, water stopper
The four components
- Tie rod — the steel rod itself, threaded along its entire length so it can be cut to any wall thickness on site.
- Cone (D-cone) — a truncated cone that screws onto each end of the rod, creating the wall-face pocket after rod removal. Stays in the concrete if the rod is removed; pulled with the rod if lost-tie.
- Plate-anchor / hex nut — bears against the waling beam outside the formwork, transferring tension into the rod.
- Water-stop plate (optional) — welded disc at mid-length, creates labyrinth seal against water seepage.
4. Hydrostatic load and rod sizing
Hydrostatic pressure of fresh concrete at depth h is:
For h = 4 m: p = 100 kPa = 100 kN/m².
The load per tie rod is hydrostatic pressure × tributary area:
- Vertical spacing s_v = 0.5 m, horizontal spacing s_h = 0.6 m → tributary area = 0.3 m²
- At the deepest tie (h = 4 m): F = 100 × 0.3 = 30 kN per tie
- DW15 allowable working load = 90 kN → safety margin 3.0 ✓
Working load tables — Chontan tie rod system
| Rod size | Rod cross-section (mm²) | Allowable WL (kN) | Allowable formwork load (kN) | Cone UTS (kN) |
|---|---|---|---|---|
| DW15 | 177 | 90 | 150 | 170 |
| Rd16 | 153 | 90 | 150 | 165 |
| Rd20 | 227 | 140 | 230 | 250 |
| Rd24 | 327 | 200 | 320 | 340 |
Pour rate matters. The hydrostatic formula assumes continuous fluid pressure to full depth. In reality, concrete starts to set after 60–90 minutes, reducing pressure on the formwork below the freshly-poured zone. CIRIA 108 (UK) and DIN 18218 (Germany) give reduction factors based on pour rate: slow pour (< 1 m/h) → full hydrostatic; fast pour (> 3 m/h) → may need higher safety margin or stiffer formwork.
5. Water-stopping and lost-tie systems
For water-retaining structures (basements below water table, pools, tanks, treatment plants), the tie path through the wall is a leakage route. Three solutions in increasing rigour:
| System | How it works | Water-tight? | Cost |
|---|---|---|---|
| Tie rod with water-stop plate | Welded disc mid-rod creates labyrinth path | ≤ 1 bar; suitable for non-pressurised basements | 1.5× standard rod |
| Lost-tie + galvanized sleeve | Rod stays in concrete, threaded inside a HDG sleeve that's bonded to concrete | ≤ 5 bar; suitable for water tanks | 2.5× standard rod |
| Bitumen-coated lost-tie | Bitumen wrap on stop plate prevents capillary water entry | ≤ 10 bar; suitable for tunnels, pressurised tanks | 3.5× standard rod |
| Stainless lost-tie + bentonite | A4 stainless rod + swelling bentonite collar | ≤ 20 bar; sewage and chemical containment | 6× standard rod |
For each system, the cone pockets at the wall surface must still be sealed after rod removal — typically with hydraulic non-shrink grout, with a final waterproofing coat applied to the entire wall surface.
6. Standards governing this product
| Standard | What it governs | Why it matters |
|---|---|---|
| DIN 488 | Reinforcement steel — covers Dywidag DW thread profile | Tie rod thread geometry must conform. |
| DIN 18218 | Pressure of fresh concrete on vertical formwork | Sets the design load formula used to size tie rod spacing. |
| CIRIA Report 108 | UK equivalent to DIN 18218 | Used in UK/Commonwealth formwork design. |
| EN 10204 3.1 | Mill certificate format with batch tensile data | The cert grade an independent QA can audit. |
| ISO 1461 | Hot-dip galvanizing thickness ≥ 45 μm | Mandatory for lost-tie systems exposed to wet/coastal environments. |
| EN 1090-2 | Execution of steel structures | Sets tolerances for thread straightness and dimensional inspection. |
7. Chontan DW15 — key specifications
| Parameter (DW15 class, 2.5 m rod) | Chontan DW15 |
|---|---|
| Thread spec | DW15 (DIN 488 / Dywidag) |
| UTS (typical) | 800 N/mm² |
| Allowable formwork load | 150 kN |
| Standard rod length range | 0.5 – 6.0 m + custom |
| Straightness tolerance | ≤ 1 mm / m |
| Standard finish | Plain, zinc-plated, HDG, A4 |
| Water-stop variant available | ✓ 60 mm welded plate |
| EN 10204 3.1 cert | ✓ default |
| Indicative FOB price / m (5k m lot) | USD 1.20 – 1.80 |
| Lead time | 20 – 35 days |
| OEM private label | ✓ from 10,000 m |
For a contractor running 100,000 m of tie rod per year (a medium-size concrete construction operation), China-direct sourcing delivers a substantial annual cost saving. Quality risk is low — the Dywidag thread spec is decades-old and universally machined to tight tolerances; the only relevant QA is straightness and UTS.
8. 12-step installation procedure
- Receive rods at site, verify length, straightness (eyeball ≤ 1 mm/m over 2 m), thread condition.
- Verify cone match — DW15 cones onto DW15 rods. Cross-check with thread gauge if any doubt.
- Assemble formwork panels per system manufacturer's drawing — pre-drilled holes at standard spacing (typical 0.5 m × 0.6 m grid).
- Thread cones onto rod ends — both sides. Cone bottoms out flush against rod end shoulder.
- Insert assembled rod through pre-drilled formwork holes from one side, push through both panels.
- Install plate-anchor / waling beam on each side. Slide hex nut onto rod end against waling.
- Tighten hex nuts to formwork manufacturer's torque (typically 80–120 Nm for DW15 — finger-tight then quarter-turn).
- Verify no slippage — pull on rod end manually; rod must not slide through cone.
- Pour concrete at design rate (typically ≤ 1.5 m/hour for DIN 18218 hydrostatic; faster if you've sized for full hydrostatic load).
- Cure to f_c ≥ 5 N/mm² — typically 12–24 hours depending on cement type and ambient temperature.
- Unscrew hex nuts, remove waling and plate-anchor.
- Withdraw tie rod by turning counter-clockwise from one side; the rod unscrews from the cones and pulls through the wall, leaving the cones embedded.
Watch the installation video
9. Removing the rod and patching the pockets
After concrete cure, the rod is unscrewed from one side (the cones stay in the wall) and pulled through. The cones leave frustum-shaped pockets 22 mm dia × 25 mm deep on each wall face. Patching protocol:
- Clean the pocket — compressed air to remove dust and concrete laitance.
- Wet the pocket — saturate surface but no standing water.
- For interior / non-exposed walls: press in a plastic cap (provided by formwork supplier) — cheap, fast, watertight.
- For exterior / water-retaining walls: fill with non-shrink hydraulic cement grout, trowel flush. Apply waterproofing membrane over the entire wall surface afterwards.
- For exposed architectural walls: use a coloured-grout patching system (Sika MonoTop, Mapei Mapegrout) matching the wall colour. Trial samples first.
10. Reuse and inspection
Through-rods (the standard case) are reusable for 50–100 pour cycles. Inspect after each pour:
- Bend test: roll the rod on a flat surface. If the gap exceeds 2 mm/m, reject.
- Thread inspection: nut should turn freely along the entire length. Stripped or chipped threads — reject.
- Surface corrosion: light surface rust is OK (wire-brush before next use); deep pitting → reject.
- Cone wear: cones outlast rods 2:1. Reject when the internal thread shows visible wear or the seat surface is no longer flat.
Lost-tie rods are single-use by definition.
11. Procurement & cost tips
- Buy by the kilometre. Rod price is quoted per metre; transport is by weight. 100 km of DW15 weighs ~50 tonnes — fits in 2 × 40 HC containers. MOQ of 5,000 m is the typical first price-tier; 80,000 m typically drops FOB price by 15–22% (per-piece tooling allocation drops at scale).
- Single-supplier matched system. Rod + cone + plate-anchor + nut from one source. Cross-sourcing voids any system warranty and increases the risk of mismatched threads.
- Specify straightness in writing. Cheap suppliers cut corners on straightness — and a bent rod fails to thread cleanly. "Straightness ≤ 1 mm per metre" is the standard floor.
- Pre-order custom lengths for repetitive elements. If you have 5,000 walls of identical 250 mm thickness, ordering 5,000 × pre-cut 0.5 m rods (with one cone already threaded) saves site labour ~3 minutes per tie.
12. Frequently asked questions
What is a formwork tie rod?
A steel rod with coarse thread along its length (typically DW15, Rd16 or Rd20) that ties the two faces of a concrete wall formwork together against the hydrostatic pressure of fresh concrete. The rod passes through both formwork panels and through the wall void, terminating in cone nuts on each side that tension against waling beams. After concrete cure, the rod is unscrewed and either removed (with the cone leaving a frustum-shaped pocket) or stays in place (lost tie rod) depending on whether the wall is exposed.
What is the difference between DW15 and Rd16 / Rd20 tie rods?
DW15 (Dywidag system, 15 mm root diameter, 17 mm outer thread diameter, 7.5 mm pitch) is the most common European formwork tie standard. Rd16 (round thread 16 mm, 8 mm pitch) and Rd20 (20 mm, 10 mm pitch) are alternative coarser threads used in heavy-duty applications. DW15 carries 150 kN allowable tension; Rd20 carries 230 kN. All three are mutually incompatible — you cannot screw a DW15 nut onto an Rd16 rod.
What is the working load of a tie rod?
For DW15: rated working load is 90 kN (with safety factor 1.6 against yield) and 150 kN allowable in formwork applications. For Rd16: 90 kN working / 150 kN allowable. For Rd20: 140 kN working / 230 kN allowable. The governing load is hydrostatic pressure × tributary area: e.g. a 4 m high wall pour with 50 kPa/m gives ~80 kPa at the base, times 0.4 m × 0.6 m tributary area per tie = 19 kN — well within DW15 capacity. Always check both the design load and the formwork manufacturer's rod spacing.
What is a water-stopping tie rod?
A tie rod with a welded water-stop plate (typically 60 mm diameter steel disc) at mid-length. The plate creates a tortuous path through the concrete that prevents water seepage along the tie path after the rod is removed. Mandatory in water-retaining structures (basements below water table, water tanks, swimming pools, sewage treatment plants). The plate must be hot-dip galvanized for corrosion resistance after the rod is removed — the cone pockets at the wall surface get sealed with hydraulic mortar.
Can the tie rod be reused?
Yes for through-rod systems (rod removed after cure): 50–100 cycles typical, limited by thread wear and slight bending. Inspect the rod after each pour — reject if any plastic deformation, thread damage, or pitting visible. The cone nuts have longer life (~200 cycles) because they don't bend. Lost-tie systems (rod stays in the concrete) are single-use; only the cones are reused. For water-retaining walls, lost-tie with water stopper is standard practice.
What concrete strength is required before the tie rod can be removed?
Typically f_c ≥ 5 N/mm² (early set, 12–24 hours depending on cement type) is sufficient to remove tie rods without spalling around the cone pocket. The rod itself doesn't carry load after concrete sets; removal is purely mechanical — unscrew the cone, pull the rod through the wall, patch the pockets with non-shrink grout. Wait longer (f_c ≥ 10 N/mm²) before stripping the formwork itself.
What corrosion protection should I specify?
For through-rod (removed after cure): plain (uncoated) steel is standard — the rod is reused and any rust is removed by wire-brushing between pours. For lost-tie (stays in concrete): hot-dip galvanized HDG ≥ 45 μm is standard. For water-retaining lost-tie with water stopper: stainless A4 (316) or HDG with bituminous coating on the stop plate. Chontan supplies all three finish options from stock.
How are tie rod pockets patched after removal?
After rod removal, each cone leaves a frustum-shaped pocket about 22 mm dia × 25 mm deep on each wall face. Standard practice: (1) clean the pocket with compressed air, (2) wet the concrete face, (3) press in a tapered plastic cap (provided by the formwork manufacturer) or fill with non-shrink cement grout, (4) trowel flush. For exposed architectural concrete, use a coloured-grout patching system that matches the wall finish.
What documentation should the supplier provide?
EN 10204 3.1 mill certificate per heat batch with tensile data (UTS ≥ 700 N/mm² for DW15), thread gauge inspection report (go/no-go on every batch), straightness inspection (≤ 1 mm per metre), dimensional inspection per DIN 488 / Dywidag spec. For HDG variants, ISO 1461 coating thickness report. Chontan supplies all of these with every export shipment.
References
Who wrote this, and why you can check it
We make these parts, we don't resell them
Qingdao Chontan Industry has been supplying the precast and prestress industries for over 20 years, from our own factory in Chengyang District, Qingdao. Everything in these guides comes from producing, testing and shipping the components they describe — not from a catalogue.
Our own test floor, not an outsourced claim
Anchors are verified in-house before they leave:
- 30 T – 300 T universal tensile testers for pull-out and tensile testing
- Low-temperature impact testing — the test that catches brittle behaviour
- Metallographic structure analysis and hardness testing
- Material sampled for microscopy before the first manufacturing operation
- Dimensional inspection against drawings, with purpose-made gauges during production
Facts are attributed to the standard, not to us
Where these guides quote a limit — a load, a wear limit, an inspection interval, a cover formula — it is attributed to the standard that sets it (EN 1992, EN 10204, EN 13101, DIN 405, VDI/BV-BS 6205, ACI 318, the Machinery Directive). We tell you which document to read, so you never have to take our word for it.
What we will not do
- We do not publish another manufacturer's load tables as our own data.
- We do not quote a rating without its conditions — concrete grade, embedment, edge distance.
- Illustrative numbers are labelled illustrative; design from your supplier's tested data.
- Where we are uncertain, we say so and point you to the primary source.
Need DW15 / Rd16 / Rd20 tie rods at China-direct prices?
20+ years export experience. Plain, zinc, HDG and A4 stainless finishes. Water-stopping variant in stock. MOQ from 5,000 m. EN 10204 3.1 certs included. Quote against your drawing in 24 hours.
