# Zinc phosphate pretreatments

Supplied zinc-phosphate conversion chemicals, product-specific properties, coating-mass units, and limits of formulation and performance claims.

Reviewed: 2026-10-30

Tags: chemicals, formulations, conversion-coatings

## Identity and related materials

Henkel’s zinc-phosphate **M-ZN 958 MU** TDS reports **pH approximately 1.0 for the supplied clear green liquid**, with sample preparation and test temperature unstated. The separate **958 R-UK** component lists pH below 2.0. Supplied values do not establish a bath setpoint. [958 MU TDS](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-958-MU-en_GL.pdf) [958 R-UK TDS](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-958-R-UK-en_GL.pdf) Philippine Parkerizing distinguishes zinc, iron, manganese and zinc-calcium families. [Philippine Parkerizing, phosphating chemicals, undated](https://philparkerizing.com/products/chemical-products/phosphating-chemicals/)

Several similar names describe different subjects:

- An amorphous iron-phosphate pretreatment is a separate product class. Henkel describes M-FE 3990 as forming an amorphous layer composed mainly of iron phosphates. That description does not identify a crystalline zinc-phosphate film. [Henkel M-FE 3990, Ireland product page, undated](https://next.henkel-adhesives.com/ie/en/products/surface-treatments/central-pdp.html/bonderite-m-fe-3990/BP000046.html).
- Manganese-phosphate products are distinct from zinc-phosphate products that also contain manganese. Philippine Parkerizing lists manganese-based PALFOS separately from zinc-based PALBOND. [Manufacturer comparison](https://philparkerizing.com/products/chemical-products/phosphating-chemicals/).
- Zinc-phosphate pigment is an ingredient for organic coatings. HALOX describes its Zinc Phosphate as an inorganic corrosion inhibitor for water- and solvent-based coatings. A pigment dispersed in paint is not the conversion film beneath paint. The last distinction is synthesis of the stated product roles. [HALOX Zinc Phosphate, undated](https://www.halox.com/halox-zinc-phosphate/).
- A raw salt is not a complete pretreatment formulation. GARDOBOND Z 3480 E's SDS identifies a mixture of salts, water, and acids. A disclosed salt does not identify the finished film. [Chemetall SDS, version 2.0, April 14, 2025, sections 1 and 3](https://www.conro.com/fr/downloads/Manuals/GARDOBOND-Z-3480-E-25KG-Container-SDS.pdf).

## Product identity includes the component

The BONDERITE M-ZN 958 MU TDS identifies MU as the make-up component and R-E as a replenisher. It separately names a silicofluoride additive, an accelerator, and a neutralizer. Surface conditioners such as M-AC 950 have another role. An activation product is therefore not interchangeable with the phosphate chemical merely because both belong to the pretreatment system. [Henkel 958 MU TDS, August 2016, pages 1-3](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-958-MU-en_GL.pdf).

The June 2017 R-UK sheet instead names R-UK as the replenisher. These suffixes identify distinct components and documents. Neither sheet establishes that R-E, R-UK, or another region's similarly named product has identical supplied properties. [Henkel 958 R-UK TDS, June 2017](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-958-R-UK-en_GL.pdf).

The following values describe the named liquid products in their technical-data or physical-property sections. They are not working-bath targets or film properties.

| Exact product and document                                                         | Stated form              | Reported liquid properties                            | Measurement limits                                                                                                                                                |
| ---------------------------------------------------------------------------------- | ------------------------ | ----------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| BONDERITE M-ZN 958 MU, also named Granodine 958 A, August 2016, English global TDS | Clear green liquid       | Density approximately 1.5 g/cm³; pH approximately 1.0 | Temperature, density method, and pH sample preparation are unstated. [TDS, page 1](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-958-MU-en_GL.pdf)             |
| BONDERITE M-ZN 958 R-UK, June 2017, English global TDS with UK product suffix      | Clear green liquid       | Density approximately 1.47 g/cm³; pH below 2.0        | Temperature, methods, and pH sample preparation are unstated. [TDS, page 1](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-958-R-UK-en_GL.pdf)                  |
| GARDOBOND Z 3480 E, Chemetall Ltd., Great Britain, SDS version 2.0, April 14, 2025 | Colourless to red liquid | Density 1.495 g/cm³ at 20 °C; pH 1-2                  | Density method and pH test conditions are unstated. [SDS, sections 1 and 9](https://www.conro.com/fr/downloads/Manuals/GARDOBOND-Z-3480-E-25KG-Container-SDS.pdf) |

Specific gravity is a ratio to a reference density and has no unit. Density has mass-per-volume units. A pH without stated preparation cannot be reassigned to a diluted analytical sample. These are dimensional and measurement interpretations, not additional product specifications.

## Variants and composition disclosures

Henkel describes the 958 process as nitrite-accelerated and tricationic, producing a fine crystalline zinc-phosphate film containing manganese and nickel. Its named metals are steel, galvanized steel, and zinc-nickel-alloy-coated steel. This does not establish aluminum compatibility for every 958 variant. [958 R-UK TDS, page 1](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-958-R-UK-en_GL.pdf).

M-ZN 20, formerly Granodine 20, is a different process. Its September 2023 TDS describes nitrate and nitrite acceleration and microcrystalline zinc-calcium-phosphate layers on steel and iron. The sheet calls the process one-component while separately listing an additive and accelerator. That wording does not mean the entire treatment system consists of one chemical. [Henkel M-ZN 20 TDS, pages 1-2](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-20-en_GL.pdf).

GARDOBOND Z 3480 E's SDS reports monobasic zinc phosphate, CAS 13598-37-3, at at least 20% and below 25% by weight. It also discloses phosphoric acid, zinc nitrate, and calcium nitrate. These are mixture disclosures, not a complete formula, bath analysis, or film composition. No nickel or manganese absence claim follows from their omission. [SDS, section 3, pages 6-9](https://www.conro.com/fr/downloads/Manuals/GARDOBOND-Z-3480-E-25KG-Container-SDS.pdf).

Chemetall advertises chrome- and nickel-free alternatives within its broad Gardobond portfolio. Its public page also includes iron, zinc, manganese, and titanium/zirconium technologies. The portfolio statement cannot certify a particular grade or current lot as nickel-free, chromium-free, or harmless. [Chemetall Gardobond overview, undated](https://www.chemetall.com/global/en/technologies/gardobond).

## Coating mass and conflicting units

A coating mass per unit area has units such as g/m² or mg/ft². Liquid density in g/cm³ measures something different. Neither quantity alone gives coating thickness. A thickness deduction would also require an applicable film density and a justified model of the coating.

M-ZN 20's TDS gives an example coating mass of 3-6 g/m² and explicitly allows departures with process conditions or substrate. It supplies no coating-mass test method, alloy grade, or measured specimen results for that range. It is neither a universal acceptance band nor a promise for a particular part. [M-ZN 20 TDS, page 1](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-20-en_GL.pdf).

Both 958 sheets print a typical coating-weight range of 2.0-3.5 **g/cm³**. The unit appears in the actual PDF images, not only extracted text. This is dimensionally inconsistent with mass per area. The intended area unit remains unresolved here. Replacing it with g/m² would invent a correction. [958 MU, page 1](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-958-MU-en_GL.pdf), [958 R-UK, page 1](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-958-R-UK-en_GL.pdf).

As a conditional arithmetic example, a measured coating mass of 3 g/m² over 0.10 m² corresponds to 0.30 g of coating. That calculation assumes the area basis and measured coating quantity match. It does not predict chemical consumption, deposition efficiency, thickness, or bath make-up.

**Synthesis:** descriptions such as heavy, light, fine crystalline, and thin film do not supply interchangeable coating-mass limits. Chemetall, for example, describes some Gardobond X thin-film systems as zirconium/titanium-based. The term "thin film" alone does not even establish zinc-phosphate chemistry. [Gardobond technology portfolio](https://www.chemetall.com/global/en/technologies/gardobond).

## Performance and applicability limits

The M-ZN 20 sheet makes qualitative corrosion-protection and paint-adhesion claims. It provides no salt-spray duration, paint system, adhesion method, exposure cycle, or acceptance criterion. Those claims cannot establish a comparative service life. [M-ZN 20 TDS](https://datasheets.tdx.henkel.com/BONDERITE-M-ZN-20-en_GL.pdf).

Cold-forming behavior also belongs to a coating-and-lubricant system. Chemetall describes its phosphate-free Gardo Hybrid alternative as a conversion layer with lubricant above it. This is a distinct chemistry, not another zinc-phosphate grade. Its public description supplies no friction coefficient or forming-load result transferable to zinc-phosphate pretreatments. [Chemetall Gardo Hybrid, undated](https://www.chemetall.com/global/en/technologies/gardohybrid).

The GARDOBOND SDS is hazard information, not a performance certificate. Section 2 classifies skin corrosion and aquatic hazards. Section 16 disclaims a quality specification. Supplied-product disclosures do not characterize a used bath, sludge, or coated component. [SDS, sections 2 and 16](https://www.conro.com/fr/downloads/Manuals/GARDOBOND-Z-3480-E-25KG-Container-SDS.pdf).

**Synthesis:** relevant comparison conditions include the actual alloy and surface, coating-mass method, subsequent paint or lubricant, exposure method, and failure criterion. Missing conditions leave performance unknown. A chemical name, supplier listing, or generic multimetal claim does not establish customer qualification.

## Standards and source coverage

ISO 9717:2024, edition 4, specifies requirements for phosphate conversion coatings usually applied to ferrous materials, aluminum, zinc, and their alloys. That public scope is not a declaration that any product above complies. ISO 3892:2000, edition 2, concerns gravimetric determination of conversion-coating mass per unit area. Only publisher catalog information is used here, not paid criteria or test procedures. [ISO 9717:2024](https://www.iso.org/standard/83693.html), [ISO 3892:2000](https://www.iso.org/standard/32968.html).

Coverage includes the complete four-page 958 MU and R-UK TDSs, the three-page M-ZN 20 TDS, the 38-page GB English GARDOBOND Z 3480 E SDS hosted by Conro, and the cited public manufacturer pages and ISO catalogs. Henkel's PDF generation timestamps are in November 2025; their technical revisions remain August 2016, June 2017, and September 2023. The undated web pages do not supply controlled revisions.

No complete proprietary formulation, current-lot certificate, matched corrosion or forming trial, customer approval, or regional equivalence supports this reference. Henkel SDSs for the exact listed components were not obtained. The GARDOBOND SDS does not replace them, and no GARDOBOND TDS was available to establish that product's coating performance. Bath recipes and operating or analytical-control procedures are outside this reference.

Related references are [phosphate conversion coating](../../processes/finishing/phosphate-conversion-coating.md) and [Surface-finishing processes](../../processes/finishing/index.md).