# Cold anodizing sealing

Cold sealing after aluminium anodizing: chemistry variants, ageing, dye-fixation distinctions and bounded seal-quality tests.

Reviewed: 2026-11-01

Tags: processes, finishing, anodizing, sealing

Henkel's nickel-free **BONDERITE M-ED 11150** system specifies a **35–40°C first treatment** and heated ageing and excludes dye colouring. **SurTec 351** is room-temperature dye fixation followed by hot sealing. Specify the full sequence and the acceptance method for the selected chemistry and colour. [Henkel technical data sheet](https://datasheets.tdx.henkel.com/BONDERITE-M-ED-11150-en_GL.pdf) [SurTec 351](https://www.surtec.com/en/products-services/surtec-351/)

## Clarify the operation

Cold sealing treats a porous anodic layer after anodizing and any coloring step. Qualify the chemistry, ageing and seal acceptance together. [Alufinish: what happens during cold sealing](https://alufinish.de/en/what-happens-during-cold-sealing/)

Use an unambiguous purchase description such as anodizing plus the agreed colouring and sealing system. Include substrate alloy, coating requirements, significant surfaces, appearance and intended service. Do not let a shorthand request for “cold anodizing” decide the process when the actual requirement is a seal after anodizing.

## Chemistry families and named examples

Traditional nickel-based cold sealing uses reactive species that enter the porous coating and form poorly soluble compounds. Alufinish's **13 January 2023** explanation distinguishes this precipitation mechanism from hot-seal swelling and describes nickel-containing systems such as **Alfiseal 982/982/5**. It also discusses nickel-related colour cast and process sensitivity. These details belong to the described chemistry, not every low-temperature post-treatment. [Alufinish technical explanation](https://alufinish.de/en/what-happens-during-cold-sealing/)

SurTec's portfolio identifies **356 IT Hardwall** as a nickel-fluoride powder cold seal and **372 Hardwall** as a liquid product with a balanced nickel/fluoride ratio. Nickel-free processes also exist, but the words “nickel-free” do not by themselves establish temperature, colour compatibility or completion of the sealing sequence. [SurTec anodizing portfolio](https://www.surtec.com/en/applications/metal-pre-treatment/anodizing-portfolio/)

A useful counterexample is **SurTec 351**: its product page calls it nickel-free **dye fixation**, operated at room temperature and combined with subsequent hot sealing. It should not be treated as evidence that any room-temperature colour-fixing dip is a complete cold seal. [SurTec 351](https://www.surtec.com/en/products-services/surtec-351/)

Henkel's **BONDERITE M-ED 11150**, TDS **April 2020**, describes a nickel-free sealing technology used with companion products. The sheet identifies a **35–40°C** first treatment and a heated ageing stage, and explicitly states that the system is **not suitable for dye colouring**. This is a named product limitation, not a rule for all nickel-free systems. Obtain the applicable current instructions for the complete system before specifying it for a coloured part. [Henkel technical data sheet](https://datasheets.tdx.henkel.com/BONDERITE-M-ED-11150-en_GL.pdf)

## Complete sequence and ageing

“Cold” need not mean that every stage uses ambient-temperature water. Alufinish describes a two-step route with subsequent hot-water ageing, even where initial seal values reach a target after waiting. It associates this stage with accelerated pore closure and reduced brittleness/microcracking sensitivity. Do not omit the second stage solely because a freshly treated coupon produces a promising result. [Alufinish: ageing explanation](https://alufinish.de/en/what-happens-during-cold-sealing/)

Control the whole approved route: incoming oxide condition, any dye treatment, rinsing, chemical post-treatment, ageing and drying. Preserve the elapsed time and conditions between sealing and testing so repeat measurements describe comparable states. Distinguish a deliberately specified ageing treatment from uncontrolled storage time.

For a production handoff, identify the actual product combination and generation, applicable substrate/colour restrictions, required post-stage and supplier analytical controls. A supplier's technical service may need to qualify the route for the line; Henkel explicitly directs users to plant-specific working parameters. This page does not supply a universal bath make-up or operating recipe. [Henkel application scope](https://datasheets.tdx.henkel.com/BONDERITE-M-ED-11150-en_GL.pdf)

## Specifications and current-edition boundaries

QUALANOD's current specifications page lists **edition 1 July 2026**, superseding **1 January 2026**, and states that documents are available by written request. A publicly indexed January excerpt should therefore not be presented as the current detailed acceptance requirements. Obtain the ordered edition and applicable updates when claiming QUALANOD conformity or using its process approvals. [QUALANOD current edition](https://www.qualanod.net/specifications.html)

Also keep a process approval, a supplier's general performance statement and acceptance of a production lot separate. Each answers a different question. Record which coating specification and test criteria govern the delivered parts rather than inferring compliance from the chemical trade name.

## What seal-quality tests establish

| Method | Scope and important limitation |
| --- | --- |
| ISO 2143:2017 | Dye-spot test after acid pretreatment estimates loss of absorptive power; not a universal colour or corrosion test |
| ISO 2931:2017 | Admittance assesses sealed-coating quality; results from different sealing routes are not necessarily comparable |
| ISO 3210:2025 | Destructive acid-solution mass-loss methods assess seal quality within their stated applicability |

**ISO 2143:2017**, edition 3, published **October 2017**, confirmed **2023**, excludes deeply coloured coatings, coatings below 3 µm and specified alloy/supplementary-treatment cases. Its scope also cautions about some hydrothermal additives. Check applicability before selecting it for a dyed or specially treated part. [ISO 2143](https://www.iso.org/standard/70154.html)

**ISO 2931:2017**, edition 4, published **November 2017**, confirmed **2023**, applies to aqueous-sealed coatings with sufficient test area and thickness above 3 µm. It warns that cold- and hydrothermally sealed results need not be comparable, and identifies alloy-dependent comparison limits. Agree the acceptance use between anodizer and customer. [ISO 2931](https://www.iso.org/standard/70155.html)

**ISO 3210:2025**, edition 5, published **October 2025**, distinguishes methods with and without prior acid treatment. It notes potential applicability beyond hydrothermal sealing and use as a destructive reference test. Its exclusions include hydrophobic treatments, chromic-acid coatings and specified hard-type/dichromate cases. Do not replace those applicability checks with an unspecified “acid test.” [ISO 3210](https://www.iso.org/standard/88866.html)

A satisfactory seal-quality result does not alone qualify outdoor lifetime, UV colour stability, wear, chemical cleaning or every corrosion exposure. Specify additional performance tests where those functions matter, with the actual alloy, coating thickness, colouring and post-treatment represented.

## Original area-normalization illustration

Assume a flat **50 × 100 mm** coupon, with both large faces exposed and edges deliberately excluded from the evaluated area. One face is **50 cm²**; both total **100 cm² = 1 dm²**. A hypothetical measured loss of **24 mg** therefore gives:

`mass loss / evaluated area = 24 mg / 1 dm² = 24 mg/dm²`.

Incorrectly counting only one face gives **48 mg/dm²**, twice the correct value for these assumptions. This is an original dimensional calculation, not an ISO procedure or acceptance limit. Actual testing must follow its specified specimen preparation, exposed-area definition, timing and method; real edges, holes or masking can change the area.

## Useful delivery record

Record alloy/temper, anodizing and colour requirements, coating thickness, seal chemistry/product combination, ageing sequence, significant surfaces and agreed appearance sample. Include test method/edition, specimen representativeness, time since treatment, results and acceptance criteria. Preserve the supplier instructions and SDS for the actual chemicals used; nickel-free is a composition statement rather than a universal handling guarantee.

The Alufinish article and Henkel TDS are dated above. SurTec's live product pages have no verified technical revision date here. QUALANOD's current-edition notice is cited for edition status only; its July 2026 technical clauses were not available for direct review. The calculation and proposed handoff fields are original guidance.