Wash primer vs. shop primer

Q. What is G90 HOT-DIP GALVANIZED

A. Hi,

It means a coating weight of 0.90 ounces per square foot.

Regards,

A. Most powder coat operations call for a minimum of an iron phosphate prior to paint. You will get better overall results from zinc phosphate, but it costs more to operate.

A. I would suggest that you evaluate a product that is called two pack wash primer in the USA (the one pack version is not for you). You may be able to obtain it from an auto repair shop. Because it contains phosphoric acid its adhesion to metal substrates is outstanding. Mix only sufficient for one day as beyond this time it will jell. It is now considered operator and environmentally unfriendly due to the chromate content but is still sold because there are very few alternatives... also click on the image to the left, you may find an American equivalent to our Anoprime.

A. Dear Jeff. Vinyl wash, wash primer and etch primer is name used to cover the same product. This material was developed by the US Navy around 1940. It is either supplied as a two pack material primer and catalyst or a three pack, primer, catalyst and thinner.
The product proved so successful that it is still being used to-day by some powder coaters. Unfortunately, they should not doing so® this is due to the fact that it contains an anti corrosion pigment, zinc chromate or zinc tetroxy chromate and we have all heard of the H & S issues with chromates. It also contains phosphoric acid and must be based on a low flash solvent blend® methanol [affil links] and toluene. The formula can't be altered if the formulator wishes it to perform correctly® unlike a white stoving/air drying paint which can be achieved through 1000's of different formulas. Why can't it be altered? The reason for this is that each component of the formula depends upon it reacting with the other ingredients'. The water (from the methanol) along with the phosphoric acid reacts with the metal substrate. During this reaction the chromate partially converts to phosphates etc, etc. There have been several attempts to alter the base formula, substituting the chromate with a phosphate, substituting butyl alcohol for the methanol to enable use in dip tanks. Other changes were substituting the PVB resin by 50% with a phenolic or urea resin. However, none of these changes could be claimed to improve corrosion, quite the opposite. Therefore, no matter whether the product is manufactured in the USA, China or Europe if the formulator wishes to produce a true wash primer then he should follow the following formula. Part (a)10% PVB resin 2% Talc, 10% zinc chromate or ZTC, 78% meths 64 OP/toluene mix. For Part (b) mix 2-5% phosphoric acid with 95-98% Methanol. Mix parts a & b prior to use® will last 8- 12 hours before gelling.
In addition to the H & S an issue there is also environmental ones® not VOC compliant and is highly flammable. So what do we use now; zinc phosphate (effluent problems), zirconium phosphate both can be applied by dip or spray or a waterborne primer such as Anoprime.

A. Corrosion protection on mild steel is achieved by various methods dependent on the environment into which your product goes.
Best protection perhaps is by hot dip galvanizing.
Paint and powdercoating are barrier protection only and any perforation of the coating (scratch, score, chip etc) leads to corrosion at that point.
Adhesion of the coating is important, and a suitable pretreatment is required.
Powdercoating over mild steel with nothing under that powder is usually very short lived. At very minimum a zinc phosphate pretreatment should be used.
I've not heard of "vinyl wash", but it doesn't sound like anything useful.