Mordant Solution, widely known in the industry as T-Wash, is a specialized chemical pre-treatment for new, bright galvanized steel. It is an acidic copper salt solution designed to chemically etch the surface of the zinc, creating a “key” that allows paint to adhere. Without this treatment, paint applied to new galvanizing will often peel or flake off within weeks.
It is used specifically for newly galvanized metal surfaces where traditional abrasion or shot-blasting is not possible or desired. It is ideal for gates, railings, structural steel, and Zintec sheeting.
Formulated to a British Rail T wash mordant solution galvanised steel specification
Mordant solution is an excellent metal wash mordant solution for the pre-treatment and turn black galvanised steel and zintec sheeting prior to painting
Once treated, you can apply a wide range of paints to the surface.
Not sure which whether to use mordant solution or etching primer? Take a look at our Blog here
Surface Condition: The galvanised surface must be clean and free from any oil, grease, or surface contaminants.
Degreasing: It is essential to degrease the metal thoroughly before application. Use a suitable solvent or degreaser to ensure the surface is completely clean.
New Galvanised Steel: This product is specifically designed for use on new, bright galvanised steel surfaces where standard paints may struggle to adhere.
Application
Method: Apply the solution liberally using a brush or a clean rag.
Technique: Ensure the entire surface is covered. Upon application, the solution should react with the metal, turning the surface from a bright silvery appearance to a dark grey or black colour.
Reaction Check: If any areas do not turn black, it indicates the presence of grease or a factory-applied passivator. These areas must be cleaned/abraded again and re-treated with the Mordant Solution until the reaction occurs.
Rinsing: Once the surface has completely reacted and turned black, the entire area must be thoroughly rinsed with clean water to remove any excess solution or salts.
Drying: Allow the surface to dry completely before applying any subsequent primer or topcoat.
Overcoating: After the surface has been treated, rinsed, and dried, it can be primed with a suitable metal primer (such as Carboxide Anti-Corrosive Metal Primer) or a Direct-to-Metal (DTM) coating.
SDS: [Download Safety Data Sheet (PDF)]
Pack Sizes: 1 Litre, 2 Litre, 5 Litre, 25 Litre.
Coverage / Drying Times
Reaction Time: Leave on surface for 15 minutes – 1 hour.
Overcoat: Pre-treated surface should be overcoated with an appropriate primer within 48 hours. Ensure surfaces are cleaned with an abrasive pad and degreased before application. Rinse with clean water after the reaction period to remove acid residues.
Theoretical Coverage: Not specified (Product is a chemical pre-treatment wash).
Thinning and Cleaning
Thinning: Do not thin. Shake the container for approximately 30 seconds before use.
Cleaning: Use clean water to rinse residues from the surface after application. Clean tools with water.
Q: What is Mordant Solution (T-Wash)?
A: Mordant Solution, often referred to as T-Wash, is a reactive chemical pre-treatment for new galvanised steel and Zintec sheeting. It is designed to change the surface of the metal to ensure that subsequent coats of paint adhere properly.
Q: How do I know if the Mordant Solution has worked?
A: The solution is blue in the bottle, but when applied to a clean galvanised surface, it should turn the metal black. This blackening effect is a clear indicator that the chemical reaction has taken place and the surface is ready for painting.
Q: What does it mean if the metal doesn’t turn black?
A: If no colour change occurs, it usually means the surface is contaminated (often with oil, grease, or a factory-applied passivator). These areas must be cleaned or degreased more thoroughly and re-treated.
Q: Can it be used on old, weathered galvanised steel?
A: It can be used, but the reactivity of the solution decreases as the galvanising ages. Weathered surfaces may show an uneven colour change ranging from light to dark grey rather than solid black.
Q: Is it better than an etching primer?
A: T-Wash is a traditional chemical pre-treatment specifically for galvanising. While etching primers are also used for adhesion, T-Wash provides a visible reaction that confirms the surface is ready. (Palatine also offers a blog comparison for further details).
Q: What safety precautions should I take?
A: Wear PPE-chemical-resistant gloves (nitrile/neoprene), safety goggles/face shield, long sleeves and trousers, and chemical-resistant footwear.
Q: How long does the reaction take?
A: 5–15 minutes. You’ll see the surface darken or develop a grey/black etched finish as the mordant solution reacts with the galvanised coating.
Q: Can I apply it in cold/wet weather?
A: You can, but results are less reliable in cold, damp, or wet conditions.
2 reviews for Mordant Solution (T Wash)
Rated 5 out of 5
Owen Davies –
Providing you take real care, as the label suggests, to degrease the surface, this works outstandingly well and better than an aerosol product I had previously purchased from a nationwide auto parts store!
Rated 5 out of 5
David Ritchie (verified owner)–
It at first appeared to be an unnecessary extra cost and processes. However, having previously experienced paint blistering reactions having painted directly onto what I thought were well seasoned galvanized surfaces even using the recommended primer undercoat and process.
Applied this around 5 months ago in a 3 stage Mordant, Primer then Topcoat process and is looking good against a comparable now blistering primer/ topcoat without Mordant solution.
Its a major costly job trying to sort out paint problems. Fortunately for me this time its only on a small comparison test area this time.
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Owen Davies –
Providing you take real care, as the label suggests, to degrease the surface, this works outstandingly well and better than an aerosol product I had previously purchased from a nationwide auto parts store!
David Ritchie (verified owner) –
It at first appeared to be an unnecessary extra cost and processes. However, having previously experienced paint blistering reactions having painted directly onto what I thought were well seasoned galvanized surfaces even using the recommended primer undercoat and process.
Applied this around 5 months ago in a 3 stage Mordant, Primer then Topcoat process and is looking good against a comparable now blistering primer/ topcoat without Mordant solution.
Its a major costly job trying to sort out paint problems. Fortunately for me this time its only on a small comparison test area this time.