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Wash primer vs. shop primer



Q. Maybe the web readers can help. I am looking for research, opinions or ANY documentation on the use of organic pretreatment (wash primers) over iron phosphate. I have heard that there is a potential detrimental effect. Thanks.

Dave Wright [deceased]
- Mequon, Wisconsin
With sadness we note Dave's passing on Oct. 11, 2013. His longtime friend Anne Goyer offers a tribute to him in The Finishing Touch, Vol. 23 No. 4.

1999


"Industrial painting and Powdercoating: Principles and Practices"

on AbeBooks

or Amazon

(affil links)

A. Hello, Dave.

My recollection is to the effect that the wash primer depends on a reaction with the base metal in order to function properly--something I think I read in the 'Coating Clinic' column in "Products Finishing" magazine; but I have no real firsthand knowledge of this.

Such Q&A columns tend to not be well-indexed in the databases for computerized literature searches, and I couldn't find it with the Metal Finishing Information Service CD-ROM, but a manual search should find it. If you have an associate in my area s/he is welcome to spend a couple of hours thumbing through my copies if you don't have a closer source of back issues. But another solution might be to try to contact the column's author, Carl Izzo, a consultant who I believe lives in Export, Pennsylvania. Best of luck.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

P.S. to the readers: Dave has written a great series of articles on pretreatment. Please see "The Pretreatment Troubleshooter"


Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)



Vinyl Wash Primer on G-90 Hot Dip Galvanized Sheet Steel

Q. We are using a 2 Part Wash Primer Per DOD-P-15328 [affil link], following hot alkaline cleaning, rinsing, blow drying, as a pretreatment for "dry" non-oiled, non-chromated G-90 Hot Dip Galvanized Sheet Steel, for the application of a military epoxy primer, and ultimate CARC topcoat. This systems is a recommended pretreatment in Mil-Std-193 (which I know has been cancelled). My question - is this an acceptable pretreatment for G-90 zinc coated steel for the subsequent coatings application. In addition what is Mil-P-12879, this was also referenced in Mil-Std-193 as the desired pretreatment? Any and all assistance is greatly appreciated. Thank You. Sincerely, Bob Hathaway

robert hathaway
trucks - Oshkosh, Wisconsin
1999


A. Bob, Though I have never painted hot dip galvanized, I do paint a lot of zinc plated fasteners. If the part does not have a supplemental conversion coating over the zinc, then the wash primer is the way to go. (We also use DOD-P-15328) Your galvanize probably does not have a conversion coating over it.

I do not know of a Mil-P-12879, but do know a Mil-T-12879 as called in 193. I do not have a copy of it as it has been cancelled. However, 12879 cancellation notice refers to ASTM D2092 [affil link] Preparation of Zinc-Coated (Galvanized) Steel Surfaces for Painting. Depending on your contract, you may still be help to 12879, but the technical information in the ASTM is still a good reference.   ASTM 2092 Contains methods A-F for pretreating this material. Method D-Acid-base Resinous Treatment is DOD-P-15328 [affil link]. So again, this points that wash primer is the way to go.

Kelly Draper
- West Plains, Missouri



sidebar

Q. What is G90 HOT-DIP GALVANIZED

QIANGZONGLIANG KWZL
Plating shop employee - CAI JIA PO
July 9, 2008


A. Hi,

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

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)



Primer to powder coat 1008 steel?

Q. We produce small and very easy to break metal parts on steel 1008.
We are etching but the epoxy (powder coat application) and polyester (top layer & finish) have poor adhesion to the part.
I want to know any process that can help me to have better adhesion for the powder coating.
The process shouldn't include spin or fast spin, if we HAVE to spin the product should be very but very slow.
Thanks

Henry Rock
Manufacturing - Bowling Green, Kentucky
February 10, 2009



simultaneous replies

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.

James Watts
- Navarre, Florida



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.

Terry Hickling
Birmingham, United Kingdom




Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)



Dear Sir
I would like to know the difference between wash primer and shop primer and I have another question : what happen to unsaturated polyester in storage if increase in the pot life of the resin or what happen
and also for BPO what happen to it if it lose its effect or the active oxygen lost
wait your reply
thanks

Ethar Omar
formulator - Sadat, Egypt
August 26, 2009



Wash primer is a special metal primer (contains chromate pigment for corrosion resistance & phosphoric acid to improve adhesion). There is only one specific formula to achieve this. There are many hundreds of formulas to achieve a shop primer. Some shop primers are for wood others for metal & wood. I am not sure what you require for your other Q's.

Terry Hickling
Birmingham, United Kingdom




Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)



Powder coating over vinyl wash

Q. Jeff from an iron works in Grassie Ontario Canada. We have had some rusting issues for years with some of our mild steel products. After trying many products an older body man suggested I try " vinyl wash " as a primer. 18 months ago we started to powder coat all of our products. does anybody know or has tried to powder coat over vinyl wash and what was the result. is there a difference between vinyl washes manufactures? If vinyl wash is not the answer does anybody have any better suggestions? thanks in advance Jeff

Jeff Hilts
owner - Grassie, Ontario, Canada
March 24, 2010



simultaneous replies

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.

Terry Hickling
Birmingham, United Kingdom



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.

geoff_crowley
Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
crithwood logo



A. Hi. I've heard of vinyl wash primer several times in the "Paint Clinic" column by Carl Izzo in Products Finishing magazine. I think it contained hex-chrome and has consequently fallen out of favor.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




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