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Etch Primers

What is an Etch Primer

Etch Primer is a paint that is designed to physically bond itself to the substrate to which it is applied.
This is achieved by combining an acid with the paint so that the acid microscopically etches the surface of the substrate,
thus forming a physical and chemical bond between the two.
In most cases a colour will be added to the Etch Primer so that it can be seen.

Etch Primers are for the most part designed to work with either ferrous or non ferrous metals or in some cases both.
It is also advisable to use an etch primer on fibreglass and resin mouldings. Fibreglass is manufactured with a gelcoat
that is designed to be strong and durable without the need for paint.
Resin kits are manufactured using a chemical process that is very similar to two part epoxy resins.
Whilst this allows for complex parts to be moulded it can leave a surface that is 'slippery' and does not accept paint.
It is also possible for residues to leech out of the moulding and /or paint to leech into the moulding.

Two basic types of Etch Primer exist - Single pack and 2 pack, Phoenix Precision Paints can supply both types.

Single Pack Etch Primers

Single pack, as its name suggests is a one part Etch Primer where the acivating acid is already combined with the paint.
The advantage of Single Pack Etch Primer is, that apart from stirring, it is ready to be applied by brush to your substrate.
The disadvantages of Single Pack Etch Primers is that because they already have the acid in, they have a shelf life,
this life is about 12 months from the date of manufacture (NOT from the date of purchase)for this reason all
Single Pack Etch Primers manufactured by and / or supplied by Phoenix Precision Paints carry a best before end (BBE)
date on the can

Single Pack Etch Primers are only suitiable for Non Ferrous metals and fibreglass / resins. They do not have enough
acid in them to etch steel and cast iron.

Currently Phoenix Precision Paints only produce a grey single pack etch primer.

Single Pack Etch Primers can be sprayed, either with an airbrush or spraygun, But in order to spray single pack etch
satisfactorily it must be thinned about 50:50 with PQ2 etch primer thinners and sprayed at a pressure of 10 psi or below .

Both modellers and model engineers should be very wary of any etch primer sold by automotive repair or supplies shops or
any single pack etch primer that does not have an expiry or best before end date on it.
Whilst these are technically etch primers they do not have the same amount of the activating acid in them as
is in the Phoenix Precision product. Whilst these primers are fine for aluminium, which is what they are designed and
sold for, they are useless for brass and other similar non ferrous metals.
It is also reccomended that you avoid any etch primer that does not require a specific thinner.


2 Pack Etch Primers

As the name suggests 2 Pack Etch Primers (or 2 Part Etch Primers)are supplied in two parts - the Primer and an
Activated thinners. It is the activated thinners that contains the acid and thus causes the reaction in the primer.


2 Pack Etch Primers should not be confused with Two Pack Epoxy Paints. Whilst the terminology of 2 part (or pack) means the
same, the two products are as different as chalk and cheese. Two Pack Epoxy Paints are very hazardous and should only be
handled in the proper environment, 2 Part Etch Primers are essentially no more dangerous than their single pack cousins.

The disadvantage of 2 Pack Etch Primers is the fact that you have to mix the two parts together. The advantages are
numerous but include -
        the ability to use the same product on both ferrous and non ferrous metals,
        the ease of spraying and the fact that it can be brushed.
        2 Pack Etch Primers do not suffer with the limited shelf life that their single pack relatives have.



It should also be noted and remembered that all Etch Primers do not start to etch until they are dry.


Applying Etch Primers

Most of the problems both modellers and model engineers encounter with Etch Primers are caused by incorrect cleaning
and / or application of the product.
In order to ensure that the Etch Primer adheres properly to the substrate the following steps need to be followed.

Firstly put on a pair of rubber gloves, this is to ensure that you do not put fingerprints back onto the cleaned surface

Degrease the surface to be primed with the strongest solvent availiable. In most cases this will be PQ17 Pre Paint MetalCleaner for all metal surfaces and PQ19 Pre Paint Multi Surface Cleaner for fibreglass and resin mouldings.

The cleaner should be applied to a clean lint free rag, wiped over the surface and left to dry.

This should be repeated at least a further two times to ensure that the surface is clean and free from grease and dirt.

White Spirit and turpentine substitute should not be used as they are firstly not strong enough and secondly they leave a residue on the surface.

All types of household, kitchen, bathroom and toilet cleaners should also be avoided as they all have chemicals in them that are designed to leave
cleaned surfaces shiney and sparkling, whilst this is fine for your household surfaces or crockery the chemical can affect the performance of the Etch Primer to adhere to the substrate.

Stainless Steel & Galvanised Coatings

Both Stainless Steel (Chromium Steel, Nickel Chromium Steel) and Galvanised Coated Steels are designed to be a rust free finish to the material and as such they will resist any type of etch primer that is not extremely acidic, and hence hazardous to the user.

                    There is almost nothing that an amateur can do to etch Stainless Steel and our recomendation is to avoid, wherever possible, the use of this material.
                    If Stainless Steel has already been used, the only advise we can offer is the roughing up of the surface with 600-800 grade paper, cleaning the surface
                   with PQ17 and then applying the topcoat directly to the metal. Whilst this is not ideal it is the only way for the amateur.

                   Galvanized Steel is a material that has been coated with a zinc coating to prevent rusting.
                   Probably the most likely form of this that the amateur is likely to come into contact with is Zintec sheet.
                   Like all types of galvanised materials zintec has been designed to resist rusting and by default it also resists acids, hence etch primers do not work on it.
                   Unlike Stainless Steels Galvanised Steels have a problem, in that the galvanised coat will start to break down if left outside in the garden.
                   Commercial applications of galvanised steel apply a protective coat of paint to the metal by powder or dip coating.
                   As neither powder or dip coating are generally available to the amateur, the only option with galvanised steels is to leave them in the garden for
                   approximately 24 - 30 months thus starting the breakdown of the coating and allowing a two pack etch primer to get a hold.

 

The Next Step

You can now apply the Etch Primer to the substrate, only the thinnest coat is required and a second coat is not neccesary.

Etch Primers only start to work after they are dry. It is therefore beneficial to only use the thinnest coat possible.

Once applied the Etch Primer needs to be left to dry, both to allow the etching process to work and to allow the evaporation of the solvents contained
within the paint.

All Etch Primers need to be left for a minimum of 24 hours at a temperature of 18 - 20 degrees celcius to dry properly.

Whilst this is the minimum it is advisable to allow significantly longer before applying topcoats.

More paint finishes are ruined by the application of paint over Etch Primer  that is still drying than almost anything else.


All information on this page is provided in good faith, whilst all information is believed to be correct
Phoenix Precison Paints Ltd can accept no responsibility for incorrect information on this page.

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