Zinc Phosphate

paintron

Member
If you really want corrosion protection prior to painting steel, or galvanized metal, nothing beats Zinc Phosphate. It was developed by Parker chemical company, now Henkel. In crude terms it is phosphoric acid with zinc dissolved in it. From day one automobiles, tractors, or any painted products meant be outside for extended periods of time were coated with this prior to painting. When this chemical is applied to the surface of the metal substrate the acid etches the surface causing a rise in the pH at the interface. The zinc phosphate comes out of solution and forms crystals, which bond really well to the substrate and also give a very good surface for paint to stick to. The corrosion resistance of this treatment and paint is second to none. Even now no better products has come available.

For the home hobbyist or small paint shop here is simple method to apply it:

1. Purchase the solution

2. Clean the part with TSP (trisodium phosphate) and rinse well.

3. Acquire some spray equipment; I would suggest a Wagner electric spray gun. This has lots of plastic components so the acid will not harm it.

4. After a thorough cleaning, spray the part with the solution much as you would normally paint; doesn’t soak the crap out of it.
5. Wet a towel or blanket so it is just damp and cover the part. This is to keep the humidity up as it takes a while for the crystals to form.

6. The results will be a matt grey coating which is great for painting over. Once dry you can paint over it with primer and topcoat.

I think a story is the best way to explain the tricky part. Detergent has by nature a high enough pH to start the crystals to prematurely form so you need to rinse the part thoroughly.
Years ago a trade magazine on industrial painting had an article about Henkel and how they had put together a plan with Ford to do a reverse onus system on their pre-treatment systems (zinc phosphate). Ford would have Henkel take over their process and would then pay a unit price rather than directly pay for the chemicals. They had picked a truck assembly plant for the pilot and were getting all the arrangements. I had worked with Henkel products for years and wrote a letter letting them know that I’m your guy for the on-site position. First day on the job, I hung a bare steel test panel on the line, got it treated, e-coated, and top-coated. Gathered a few key people and then bent the panel, paint peeled back at the bend in a sheet. Gasps, first comment from one observer, quote “the paint and treatment or both peeling off”. My question to one of the Ford guys, what is your biggest quality problem. Their answer, chips and flakes on the final assembly line, which then had to be repaired. The following day I checked out the rinse section of the spray process and observed the many of the sprays were plugged. When the line was down for a break I got a closer look and saw wooden plugs where spray nozzles had broken. Keep in mind that unplanned down time cost the company a million dollar an hour. First order of business, have all the headers piping and nozzles replaced with quick snap plastic.

Lesson: make sure your part is well rinsed, no residual detergent. The last thing you want in the crystals prematurely precipitate out of solution.

Keep in mind the solution comes in different grades; you want the one designed for coating metal prior to painting.
 

Paintron, Is "reverse onus" supposed to be "reverse osmosis"? Also could you break down the first step a little?
 
Reverse onus means that Ford did not want to take responsibility for thier process. The chemical supplier would supply the expertise and take over this responsibility. This was a pilot project about 25 years ago, which I understand has now spread to all the assembly plant.
 
(quoted from post at 11:10:35 03/17/19) If you really want corrosion protection prior to painting steel, or galvanized metal, nothing beats Zinc Phosphate. It was developed by Parker chemical company, now Henkel. In crude terms it is phosphoric acid with zinc dissolved in it. From day one automobiles, tractors, or any painted products meant be outside for extended periods of time were coated with this prior to painting. When this chemical is applied to the surface of the metal substrate the acid etches the surface causing a rise in the pH at the interface. The zinc phosphate comes out of solution and forms crystals, which bond really well to the substrate and also give a very good surface for paint to stick to. The corrosion resistance of this treatment and paint is second to none. Even now no better products has come available.

For the home hobbyist or small paint shop here is simple method to apply it:

1. Purchase the solution

2. Clean the part with TSP (trisodium phosphate) and rinse well.

3. Acquire some spray equipment; I would suggest a Wagner electric spray gun. This has lots of plastic components so the acid will not harm it.

4. After a thorough cleaning, spray the part with the solution much as you would normally paint; doesn’t soak the crap out of it.
5. Wet a towel or blanket so it is just damp and cover the part. This is to keep the humidity up as it takes a while for the crystals to form.

6. The results will be a matt grey coating which is great for painting over. Once dry you can paint over it with primer and topcoat.

I think a story is the best way to explain the tricky part. Detergent has by nature a high enough pH to start the crystals to prematurely form so you need to rinse the part thoroughly.
Years ago a trade magazine on industrial painting had an article about Henkel and how they had put together a plan with Ford to do a reverse onus system on their pre-treatment systems (zinc phosphate). Ford would have Henkel take over their process and would then pay a unit price rather than directly pay for the chemicals. They had picked a truck assembly plant for the pilot and were getting all the arrangements. I had worked with Henkel products for years and wrote a letter letting them know that I’m your guy for the on-site position. First day on the job, I hung a bare steel test panel on the line, got it treated, e-coated, and top-coated. Gathered a few key people and then bent the panel, paint peeled back at the bend in a sheet. Gasps, first comment from one observer, quote “the paint and treatment or both peeling off”. My question to one of the Ford guys, what is your biggest quality problem. Their answer, chips and flakes on the final assembly line, which then had to be repaired. The following day I checked out the rinse section of the spray process and observed the many of the sprays were plugged. When the line was down for a break I got a closer look and saw wooden plugs where spray nozzles had broken. Keep in mind that unplanned down time cost the company a million dollar an hour. First order of business, have all the headers piping and nozzles replaced with quick snap plastic.

Lesson: make sure your part is well rinsed, no residual detergent. The last thing you want in the crystals prematurely precipitate out of solution.

Keep in mind the solution comes in different grades; you want the one designed for coating metal prior to painting.

Can you give a couple of example products you refer to as the correct solution?

Does the surface need scuffed or abraded after the process is complete before priming?
 
Some grades are for coating gun barrels or for phosphate and oil finishes.They have an accelerator added to make
more coarse crystals.
 
You can use TSP for cleaning, good for removing oil grease dirt. Not absolutely essential but works great. Just
make sure whatever you use is very well rinsed off.you want the crystals sticking to metal not soap residue.
 
This process is also known as Parkerizing,or bonderizing. The original company the developed the process was the
Parker Chemical company. Bonderite is one of the trade names it can be found under.
 
I still have a partial 5 gal pail from 25 years ago. I thought the stuff was no longer available. bright yellow in color and bare even slightly rusty metal equipment painted with it and not top coated is still rust free sitting out in weather for 2 years..
 
Bill,look at the can you have.I think it will say,zinc chromate.not phosphate.That was the stuff supposedly outlawed,although I'm not sure of that anymore.My dad used to use it on aluminum rain gutters before they started to come already anodized in colors.I still have some around,but I think you will find zinc phosphate is head and shoulders over zinc chromate for painting over.
 
The only reason the aftermarket is having difficulty finding zinc phosphate in hardware stores is few of you guys are using it. It's readily available on the internet, through I must admit a little pricey. Phosphoric acid is dirt cheap to make, its used to make Coca Coia and so is zinc the two main ingredients.

Second story; I'm currently employed at a coil coater, we paint millions of pounds of various substrates including steel. When I first started their over twenty years ago I was told they did not like using zinc phosphate much as it had a reputation of poor adhesion, sounds very familiar. Now we us it frequently and exclusively on roofing, siding, garage door prints as it greatly outperforms the other treatments we have available. We haven't seen an adhesion issue in years with this treatment.
 
They had a caustic hot water cleaning and phosphatizing wash machine for ALL sheetmetal parts from hoods, fenders, to the tiniest clips and clamps at the FARMALL Plant in Rock Island that washed, cleaned, and coating the parts for painting when I first started there in 1976, and the "Bonderizer" was older than dirt way back then.
When I ran out of work on my normal job I either had the choice of pushing a broom or hanging parts on the Bonderizer. You hung bare parts, and an hour or so later painted parts came by to be put in totes to go to the line. Was just one of five paint lines in the plant. Three years later I'm working in Material Scheduling, I'd get a laundry list of paint and quantity and size of containers, red, yellow, white, semi-gloss black, and 325 gallon totes, 55 gallon drums, or 5 gallon pails. Most came from Moline Paint Mfg, little came from local Valspar plant. Sales engineer from Moline Paint paid us a visit every week, he usually brought me the laundry list and the Paint Forman stopped on his way out those nights to make sure I phoned the order in. MPM supplied the East Moline plant, Canton, probably Melrose Park, Memphis, Indy, and some suppliers that painted finished parts. Eventually French & Hecht and Electric Wheel fit into that catagory, front wheels and dual wheels.
 
I'm pretty sure even the model A used bonderite.

I was still in college in 76. Started my first full time job in 78 on a aluminum coil line, only line in the world using E-coat.
 

Whats the difference between the Zinc Phosphate coatings you're talking about and Inorganic Zinc Silicate? I've used IOZ over clean blasted steel with great success.
 
(quoted from post at 06:18:43 03/29/19)
Whats the difference between the Zinc Phosphate coatings you're talking about and Inorganic Zinc Silicate? I've used IOZ over clean blasted steel with great success.

North Maine, I just googled it and I see that while it can work very well, the application can easily go wrong. This could make sale to the general public totally unprofitable. Where in Northern Maine are you from? I made two trips to Millinocket and north to Fort Kent this winter.
 
(quoted from post at 12:32:03 03/29/19)
(quoted from post at 06:18:43 03/29/19)
Whats the difference between the Zinc Phosphate coatings you're talking about and Inorganic Zinc Silicate? I've used IOZ over clean blasted steel with great success.

North Maine, I just googled it and I see that while it can work very well, the application can easily go wrong. This could make sale to the general public totally unprofitable. Where in Northern Maine are you from? I made two trips to Millinocket and north to Fort Kent this winter.

I was born and raised in Fort Kent. I currently reside in the Bangor area but my farm land and machinery are all up in Wallagrass.
 
I've never used zinc silicate, however a quick search showed it is more a primer than a treatment. Similar to a wash primer, zinc silicate dust ground up and mixed with a binder.
 

in the offshore marine coatings industry (my area of experience) it seems to be the standard everything else is judged by. My companies current coating spec in the best case scenario is white metal blast, spray single coat inorganic zinc silicate (we use solvent base), spray aluminum-rich mastic epoxy, then finish with either an acrylic polyurethane or polysiloxane finish coat.
 
You're in a very specialized area, wet ,salty environment. I mainly deal with environments that involve sun exposure, eg. automobiles, siding, roofing, and some chemical exposure environments such as appliance.

Coil coating covers a very large number of products, with a variety of treatments and coating's.

We have one lower tier treatment using Chrome and silicates used on steel. Used on interior closet doors.

A copolymer using urethane should be fairly high end and helps mitigate the brittleness of the acrylic.
 
(quoted from post at 11:11:15 03/29/19)
(quoted from post at 12:32:03 03/29/19)
(quoted from post at 06:18:43 03/29/19)
Whats the difference between the Zinc Phosphate coatings you're talking about and Inorganic Zinc Silicate? I've used IOZ over clean blasted steel with great success.

North Maine, I just googled it and I see that while it can work very well, the application can easily go wrong. This could make sale to the general public totally unprofitable. Where in Northern Maine are you from? I made two trips to Millinocket and north to Fort Kent this winter.

I was born and raised in Fort Kent. I currently reside in the Bangor area but my farm land and machinery are all up in Wallagrass.


North Maine, is that your poly tank with a solar panel on top of it up on the hilltop behind Track Down?
 
I believe that would belong to the Guimond?s. They have the cattle operation at the base of the of the big
hill headed into FK from Track Down. My land is across the river from track down... part of the ?beautiful
view? you see from Track Down is my land on the other side of the valley on Strip Road.
 
(quoted from post at 17:36:51 03/29/19) I believe that would belong to the Guimond?s. They have the cattle operation at the base of the of the big
hill headed into FK from Track Down. My land is across the river from track down... part of the ?beautiful
view? you see from Track Down is my land on the other side of the valley on Strip Road.

Very nice looking land. Is the Oliver an 1850?
 
(quoted from post at 21:50:48 03/29/19)
(quoted from post at 17:36:51 03/29/19) I believe that would belong to the Guimond?s. They have the cattle operation at the base of the of the big
hill headed into FK from Track Down. My land is across the river from track down... part of the ?beautiful
view? you see from Track Down is my land on the other side of the valley on Strip Road.

Very nice looking land. Is the Oliver an 1850?

That sad old Oliver isn’t mine- I’m not sure what model it is. It’s been sitting for at least 10 years.

Paintron- I found some Henkel Bonderite Zinc Phosphate solution sold to the aircraft community-

https://www.skygeek.com/henkel-turco-594335-galvaprep-5-gallon.html

Is this the same stuff you recommend using? It says it’s for galvanized surfaces but it also says it’s a zinc phosphate product.
 
Zinc phosphate covers zinc and steel, just the steel takes a little longer which is why you need to keep it covered or a few hours with a damp towel, or sheet.
 
(quoted from post at 11:13:21 04/22/19) Zinc phosphate covers zinc and steel, just the steel takes a little longer which is why you need to keep it covered or a few hours with a damp towel, or sheet.

Is it important to keep the towel from touching the surface, or does it contact it directly?

How do you know if you got too much treatment on, i.e. caused a failure with it? Are there some indicators for this?
 
The towel touching will not matter the reaction is happening at the metal chemical interface. It's a self limiting reaction, as the pH increases the phosphoric acid etches the metal and crystals form preventing further crystal growth.
 
(quoted from post at 12:26:52 04/23/19) The towel touching will not matter the reaction is happening at the metal chemical interface. It's a self limiting reaction, as the pH increases the phosphoric acid etches the metal and crystals form preventing further crystal growth.

Is there another detergent/rinse stage necessary after the reaction is done to remove remaining acid?
 
You can give it a quick rinse with water, let it dry and paint. Good thing is you don't have to be in a hurry to paint. I have lab panels that are years old with no rust along as they are keep dry. Paint sticks like sh*t on blanket due to immense surface area of the crystals. Our garage door product routinely passes 0T bend no cracking no removal.
 

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