Hot-water anodizing sealing

For an example 100 × 50 × 1 mm coupon coated and exposed on both faces and all four edges, area is 1.03 dm². A loss of 6 mg gives 5.83 mg/dm². Counting one 0.50 dm² face instead gives 12 mg/dm². Use the specified test's area, exclusions and acceptance limit.

Hot-water sealing hydrates an existing porous anodic layer. HAI describes boehmite formation and color retention for its process. Use the qualified sealing route and acceptance method. HAI, sealing

The mechanism is more complex than imagining a solid plug dropped into every pore mouth. A 2021 Corrosion Science study used microscopy and compositional analysis to examine dissolution and precipitation of boehmite during hot-water sealing. Its investigated films developed a layered structure rather than simple uniform pore narrowing. This supports treating oxide condition and process history as relevant, without transferring a laboratory schedule to production. Original research, mechanism of hot-water sealing

Define the intended finish

Identify alloy/product form, anodizing process, coating thickness, clear or colored condition, significant surfaces, final service, and applicable specification. Sealing is not automatically appropriate for every anodic coating. HAI notes that leaving a surface unsealed can be useful for subsequent bonding or painting, and that hydrothermal treatment affects oxide hardness. Resolve those choices against the complete finishing system; do not omit or add a seal solely because a surface is described as “anodized.” HAI, sealing and subsequent treatment

Distinguish plain-water hydrothermal sealing, hot-water processes with additives, mid-temperature proprietary seals, and cold impregnation/ageing routes. They can have different chemistry, rinsing, timing, and qualification requirements. A nickel-free requirement does not by itself identify a plain-water process, and a clear appearance does not identify seal chemistry.

For example, Henkel's April 22, 2026 announcement describes BONDERITE M-ED 11204 as a nickel-free mid-temperature system operating at 85°C, contrasted with conventional hot sealing. That is a separate named system, not authorization to lower an existing hot-water bath temperature. The announcement reported provisional QUALANOD approval at that date; it is not evidence of a later final approval or of suitability for every coating/application. Henkel, dated product announcement

Water quality, additives, and loading

Henkel's BONDERITE M-ED 11001 TDS, August 2017, describes an anti-smut additive with separate hot-sealing and ageing conditions. It identifies incompatible ions including fluoride, phosphate, silicate, copper, and iron. These are product-specific controls, not universal bath limits. Henkel, August 2017 TDS

The bulletin defines pH measurement temperature and contamination-dependent bath life. Establish supplier-approved analysis, replenishment, and replacement criteria. Acceptable pH alone does not establish low contamination or adequate sealing; retain individual-ion and performance checks where required. Henkel, bath controls

Review load mass, rack arrangement, bath circulation, heat recovery after immersion, and access to recesses. The heater controller reading alone does not establish the condition at every surface of a dense load. Record how the qualified process defines start of timing and verifies its thermal condition. This page provides no generic temperature, minutes-per-micrometre rule, or additive concentration for production.

Openings, pockets, and enclosed geometry affect wetting, solution exchange, drainage, and subsequent drying. Define which internal surfaces must be anodized and sealed; confirm that the preceding anodizing stage actually formed the required coating there. Sealing cannot repair an absent oxide layer. Review retained solution and staining at exits as part of the process trial and final cleaning route.

Current specifications versus legacy instructions

QUALANOD's official public listing identifies Specifications for the Qualanod Quality Label for Sulfuric Acid-Based Anodizing of Aluminium, edition July 1, 2026, and General Regulations I–VIII version 11 of the same date. It states that these supersede January 1, 2026 and may be supplemented by update sheets. The full current documents are available on written request. This reference uses that page for edition status only; it does not present technical clauses from an older downloadable edition as current requirements. QUALANOD, current specifications

ISO 3210:2025, edition 5, published October 2025, supersedes ISO 3210:2017. Its public scope describes destructive mass-loss methods using a phosphoric-acid-based solution: Method 1 without prior acid treatment, and Method 2 with prior acid treatment. Method 2 addresses outdoor architectural applications; Method 1 can suit less severe/decorative/protective applications. ISO 3210:2025

That scope excludes hard-type coatings normally left unsealed, dichromate-only sealed coatings, chromic-acid anodic coatings, and coatings made hydrophobic. It also identifies mass-loss testing as a possible reference when dye-absorption or admittance results are disputed. Select the applicable method and acceptance requirement explicitly; the existence of an ISO test does not supply every customer's pass/fail limit. ISO 3210:2025, applicability

The Henkel TDS references an older phosphoric/chromic test route. Its August 2017 header is distinct from its later digital-generation timestamp. Do not relabel that procedure ISO 3210:2025 or infer later-edition compliance; obtain the applicable current procedure and supplier confirmation. Henkel TDS, test references and edition

Original calculation: mass loss needs the correct area

Use the hypothetical 100 × 50 × 1 mm coupon, with all faces and edges coated and exposed and no excluded areas.

Area = 2(100 × 50) + 2(100 + 50) × 1 = 10,300 mm² = 1.03 dm².

If the measured mass difference is 0.006 g, that is 6 mg. The normalized loss is:

6 / 1.03 = 5.83 mg/dm².

One face gives 6 / 0.50 = 12 mg/dm². Follow the specified preparation, conditioning, weighing and reporting rules for an acceptance decision.

Inspection and production handoff

Separate the required appearance, coating thickness, seal quality, corrosion performance, and downstream compatibility. A clean-looking surface does not demonstrate adequate sealing, and a seal-quality result does not independently prove color matching or every service-exposure requirement. Define representative specimens, timing/conditioning before testing, sampling, and required records against the applicable specification.

Provide the part revision/alloy, anodic coating/process and thickness, coloring route, selected sealing system, specification editions, significant/internal surfaces, and subsequent paint/bonding requirements. Retain qualified load/thermal and bath-control instructions, rinse/dry/handling provisions, and the specified test results. Review a change of additive, dye, water source, load configuration, or test edition before treating it as equivalent production.

Related reference

Surface-finishing processes