Which metal primer to use? And on which surface? Questions we’re often asked here at Palatine Paints…always a prompt for a blog! Before attempting to elaborate on metal primers, we need to briefly address another question: “What’s the difference between undercoat and primer?”
Undercoats and primers serve different purposes as follows:
- Undercoat serves as a base layer to prepare your surface ready for its finish coat
- Helps you cover any inconsistencies in your surface
- Gives you a neutral surface if you’re painting over a particularly strong colour
- Note…an undercoat may follow application of a primer in some circumstances (which hopefully we clarify below)
A primer usually acts as some kind of protective or preparatory coating. Different primers can have different purposes. This often depends on the surface to which it is being applied. In general a primer will do one or more of the following:
- Provides a binding medium for subsequent coatings
- Prevents corrosion or inhibits rust in ferrous metals
- Is used over porous materials to ensure effective application and drying of subsequent coats
- Provides additional protection to a surface
- Helps paint adhere to non-porous (shiny etc) surfaces to allow subsequent coats to stick
- Can act as a barrier between the surface and finish coat, for example were surface is heated (such as hot water pipes)
- Helps durability
- Seals surfaces (especially in wood) to cover stains and prevent bleed-through of subsequent top coats
- Can create a barrier where a surface has chemical properties (such as high alkaline content) which might react and affect application of the top coat
So primers and undercoats do serve different purposes. You may find some coatings that are suitable as both primer and undercoat for certain jobs or surface types.
Which Primer or Undercoat do I need then?
Again it depends on:
- Your surface
- What it’s made of,
- Whether it has been painted or treated previously
- The quality of the surface
- What you hope to apply as a finish coat
In this blog we’re dealing with metal primers, we’ll look at other surfaces in future blogs.
So…Which Primer for Which Metal Type?
For paint purposes you can usually put your metals into the basic two categories: Ferrous or non-ferrous. For a quick way to distinguish…ferrous metals contain iron and non-ferrous metals do not.
Ferrous metals contain iron and are pretty much anywhere you look. Examples are stainless steel, carbon steel, cast iron, steel and wrought iron. Known for their tensile strength ferrous metals are widely are used in architecture, engineering and industry – from large structures like bridges, to engines, household appliances and small engineering components. Many ferrous metals are also prone to rust due to their high carbon content (the rust level will depend on the amount of iron and whether other metals such as chromium have been added).
Non Ferrous Metals
Non ferrous metals don’t contain iron. Some examples of widely used non ferrous metals are: copper; aluminium; tin; lead; zinc; titanium as well as precious metals (gold, silver and platinum etc). Non ferrous metals are used because of properties such as malleability, low weight, good conductivity and high resistance to corrosion/rust. Non ferrous metals can be found used in many areas including wiring (copper), some pipework, aircraft manufacture (aluminium) and construction (lead).
What Metal Primer do I use?
You may not need a primer at all. If metal surface is previously coated and is in good condition, an enamel based top or red oxide gloss top coat may be all you need. If your surface is any of the following: shiny; new; unsealed; likely to be exposed to humid or cold (demanding weather conditions); in poor condition, then you will definitely need a primer. The right metal primer will help prevent corrosion and rust while ensuring the top coat adheres and does not peel or flake off.
Here are our metal primers with details of what they’re used for:
Carboxide Red Oxide Primer
Red oxide primer protects against rust and corrosion. Use it on ferrous metals likely to be exposed to the elements especially cold air, damp and humidity. It is widely used in the industrial and agricultural industries for structural steel work, outdoor equipment and railings, gates etc. It gives a layer of protection before a top coat is applied and will still adhere to surfaces that already have traces of rust. As its name suggests, red oxide primer comes in ‘red’ (origins go back to ‘red lead’ paint). It is now lead free and we also make it in grey and black.
Etching Primer is used on non ferrous and galvanised surfaces to help with adhesion of subsequent coats. Etching primer effectively ‘eats into’ the ‘galv’ to prime and protect the surface at the same time. It contains acid which etches the surface (creating physical and chemical bond) and promotes adhesion of subsequent coats. You may be limited in your choice of subsequent coats when using an etching primer, so check first. It’s commonly used on railings, lamp posts and in vehicle repairs.
Mordant solutions is commonly used for treating galvanised steel and zintec sheeting before painting. It contains phosphoric acid which eats into the ‘galv’ and turns it black. This helps to indicate which parts have been treated. Mordant solution effectively “firs up” the metal surface to aid adhesion of subsequent top coats. Treatment with mordant solution allows a wider choice of primers/top coats than etching primer. Mordant solution is also known as T Wash.
Carbogalv Zinc Rich Primer
Zinc rich primer is a cold galvanising paint for application onto Iron or Steel. Our zinc rich primer can also be used as a self-finish coating or as a durable rust inhibiting primer beneath selected top coats. It is used for the protection of structural steelwork, agricultural and construction plant and machinery. Other uses include: gates; railings; iron; pipework and the rust prevention of in-situ welding work.
Carboxide Metal Primer
Carboxide Metal Primer is an anti-corrosive primer for iron and steel. It can be used with a variety of topcoats so is a good choice for metal gates, metal doors, architectural ironwork etc. Modified zinc phosphate content means that long term protection is provided. The choice of red, white or grey colour gives you several options to match your top coat. We have a variety of suitable top coats for use with Carboxide metal primer.
Fast Dry Metal Primer
Fast dry metal primer is an anti corrosive, solvent based metal primer for ferrous metals. Uses include mild steel, carbon steel, stainless steel, cast and wrought Iron. It is specially formulated for spray application and is touch dry in 15 minutes. Sometimes you’ll find this kind of primer referred to as cellulose primer. This primer gives long term protection due to modified zinc phosphate and is an excellent primer for our Fast Dry Gloss top coat. Fast dry metal primer is ideal for situations where you need to apply a primer quickly and easily.