RivetBangers.com

Hi all,

I am using zinc chromate from A/C Spruce in a spray can to prime some small parts.

Before spraying, I rough up the surface with a Scotch bright pad and then clean it with MEK or alcohol.

I've noticed however, that the after the primer dries, it's pretty delicate. I can take my fingernail and scratch it right off.

Is there anything I can do to make the primer 'stick' better? Should I alodyne the parts first?

How long are you waiting before you do the scratch test ?
In colder weather, the primer may not be fully cured enough to be scratch resistant even though it feels dry to the touch.

It really needs like 24 to 48 hours in a 60 plus temp zone to fully cure.
If that doesn't work, try a self etching primer or a two part epoxy primer that is design for bare metal.

I've never had very good luck with Zinc Chromate. We used it on the last Cherokee that we owned, and it scratched off the floor when putting the interior in a week later. Self-etching or two part epoxy is the way to go, IMHO...

Any recommendations on a self etching primer in a spray can? Where to buy?

I used Napa 7220 all through my project. Watch for sales...they run them 40-50% off quite a bit, and I would buy two boxes of 6 cans each when they did that.

Sherwin Williams has the same basic formula in their SW988 cans.

I used the NAPA 7220 also, but I actually perferred SEM from a local auto store. It seemed to adhere even better and went on more consistently between cans.

Self etching primer is the way to go. There are several different types available. I would follow Brian and Chad's recomendations. I used some but I don't have can anymore and wouldn't want to suggest anything I was't real sure about.

I called NAPA and they have the 7220. I will pick up three cans on Friday when I get home. I guess I always thought that zinc chromate was self etching. The 7220 seems to get good reviews by builders.

s10sakota wrote:Any recommendations on a self etching primer in a spray can? Where to buy?

Sherwin Williams also makes a decent Self-Etch primer in a spray can.
It's gray and goes by the designation of: 988

Wicked Stick wrote:

s10sakota wrote:Any recommendations on a self etching primer in a spray can? Where to buy?

Sherwin Williams also makes a decent Self-Etch primer in a spray can.
It's gray and goes by the designation of: 988

This sounds awfully familiar...

One last thing....since I will be using the NAPA 7220 self etching primer, do I still need to rough up the surface of the aluminum with a Scotch bright pad to help with the mechanical bond?

yes. Clean with alcohol or lacquer thinner. rough it up with Scotchbrite, clean again with thinner. It is ready for paint.
I liked to shoot parts in the evening then let them sit overnight or longer. I heat my shop with wood stove, so would leave the parts hanging over or near the stove.

for best results, Acid etch it if you can.. Alcohol and lacquer thinner will work, but youll need to scrub hard, and keep wiping until there is no discoloration on your rags.. If the rag is black, your paint/primer wont stick

Like Brian, I've used SEM throughout my project. It's very good. And for cleaning, you can save some money and get excellent results using naptha, commonly known as Coleman fuel. Just as good but much cheaper than mineral spirits, MEK, etc. The last gallon I bought cost me less than $5.00 at the local sporting goods dept. store.

Muriatic Acid is about 3 bucks a quart.. mixed with water you can acid etch 2 entire aircraft inside and out .. And it is not oil based.

just my 2 cents