Friday, July 14, 2006

Self-etching Primer

When doing major or even minor work on older cars your going to run into rust. The steel that is your car wants to turn itself back into the puffy red iron oxide that it was when it was mined. Whether you’re sanding, sand blasting or chemical striping to get rid of the paint and getting down to the metal the first thing you need to apply to the steel is self etching primer.

Self-etching primer is composed of an acid and zinc. The acid, usually phosphoric acid, forces the zinc down into the top couple of molecules of the steel. Chemically impregnating the steel like this cannot reverse the rust but it can stop in from getting worse. So it’s important that you get all of the scaly rust off.

Wipe the surface with wax and grease remover to get it clean enough so nothing interferes i.e. fingerprints. The self-etching primer is usually gray or olive drab gray but the color is just there to show you where you’ve put it on and it is very thin and one thin coat is enough. Putting more of the primer won’t make it work better. You can apply it over paint or bondo but it is only effective on bare metal. You can apply your high build primer or body filler over the self-etching primer but be careful it is not a finished product by it self.

In other words you can’t apply it and then push the car back outside, it has to have a sealed surface over it, water will reverse the reaction and will pull the zinc back out.

Self-etching primer comes as two parts or ready to spray and also comes in aerosol.

I use it when ever I see bare metal or if I’m putting one metal against another. For instance steel screws in aluminum or on welds.

Creative Commons License

This work is licensed under a Creative Commons Attribution-ShareAlike 2.5 License.

19 comments:

spiro said...
This comment has been removed by the author.
Vick said...

Thank you for that - i am currently trying to put my 39 year old land rover back together and put "what is a self etching primer?" into google because i had seen it being sold by a couple of on-line retailers and wanted to know more about it - this really helped - thank you!

Arden said...
This comment has been removed by the author.
Arden said...

Hi Jim,
Thanks for the great info. I was wondering, can parts be dipped into etching primer? I have a project where is want primer and paint inside and out on some parts I'm restoring or do you know if there is something I can use to spray paint into hollow areas of parts? I have another project of replacing the rockers on a car and I need to get paint on the inside of the panels to prevent rust.
Thanks again for the info,
Arden

Anonymous said...

Thanks Jim. Just sanded an old exhaust bracket down to bare metal and was wondering what the best thing to use was since it will be on the bottom of the car. I'm thinking I can use etching primer then undercoat-in-a-can on top of that? I know it's a little over kill but I love my Road Runner and she deserves it.

jim lyons said...

Undercoat in a can may not be quite the overkill that you imagine.
I think I'd go self-etching primer, then spray can enamel then undercoating in a can.
The enamel, and I'd use gloss is going to give you more protection than just the undercoating.
And like you said she deserves it.
Jim

Greg said...

Does any body make a clear self-etching primer?
My son is building a bobber and he wants to leave it bare metal and put a clear coat over it to protect it from rust. Do you have any suggestions on the best way to do this? Thanks

jim lyons said...
This comment has been removed by the author.
Anonymous said...

I have a 1965 Chevy Impala 2 dr HT--I have completly sandblasted the entire car--i have stripped her down to the shell on the frame. I bought 1 gallon of etching primer and a can of hardner (normal drying time). What is recommended to prep the frame for priming and painting. I was hoping to get away from blasting the frame so I dont have to remove the entire steering/A-arm assemblies and rear axle assembly with 3 arms. Any input is greatly appreciated. My email address is ddesoto103@aol.com Thank You.

jim lyons said...

Greg
I understand what you are trying to do and I've seen it done nicely a couple of times. However I've never heard of a clear and I've picked the brains of a couple of people I know and none of them has heard of a clear self etching primer.
Jim

jim lyons said...

ddesoto103
65 impala hardtop nice! That is a worthy project. You have sandblasted the body and I assume it's because of rust, correct? And the undercarriage parts are rusty too?
For this I recommend a direct to rust paint I've tried POR15 and Chassis Saver and Hammerite. I prefer Hammerite.
Remove all loose rust, dirt, grease and salt with detergent and water then clean with a solvent and rinse with clean water. Allow time to dry, then paint. Dry time is about an hour.
Jim

Erik said...

Hi I am messing around with a car I have as a daily driver ( a 81 caprice) its still a very nice car for its age, has rust starting. I wanna do this myself cheap as possible, I have a hvlp gun and a compressor. Now my uestion is it has rust starting but hasnt rusted through, now can I grind it down to bare metal por-15 the rusted areas then put bondo over that or whats the way to go? Thanx

Steve said...

I have a '97 Hyundai, I think it has aluminium panels. Will I need an etching primer for this? sparrowhawk@ihug.co.nz

chartered said...

Something which can cause problems is salt, Even a finger print can contain enough salt to cause tiny blisters under the film. Once the surface is clean wear gloves

chartered said...

Has no one heard of cathodic electro paint ,properly done it will coat all the inside bits

Unknown said...

I just went in to my local paint shop to buy some high build primer to put on the self etching primer I used in my engine compartment. I was told that because I used spray cans, the primer was no good. Now after spending 175 on a two part metal lock, I am left with the task of stripping my whole engine compartment back down. Is this true, the primer is no good if used from a spray can?

Jim Lyons said...

The only thing I can imagine is the the paint store guy misunderstood and thought you were using cheap spray can primer and wanted you to take that off. You did make it clear to him that you were using self etching spray can primer?

Bisco said...

Hello Chap,
Top blog with very informative information!
I'm Paul from Surrey, England.
I, like so many people here have a Land Rover defender 300TDI 1997 and need to understand if I can use a "Self etching primer" for both Aluminium brackets and galvanised door hinges? They are new so have no exsisting paint.
Many thanks...

Jim Lyons said...

Yes you can. Problem metals like aluminium copper and galvanized benefit from self etching primer. Metals with high electromagnetic potentials (aluminium and copper)are so electrically active that they will push the paint off from the back side. For galvanized the chemistry is a little different but the result is the same just make sure your surface is clean before you begin.
Jim