Does Primer absorb Water?????

Primer is porous. It will rust pretty easily. It should be painted.

With that said though... The 1957 Chevrolet was sold with a primer only underside, and nothing more. However, they rusted pretty badly! (Chevy figured that out years later

Anyhow... On your truck. Paint over it if you want 100% seal.

BTW... Most cars have zinc protected sheet metal these days (if not galvanized), so it may not require much of any repair. But... Both of those are just treatments, not part of the molecular structure of the metal.

Go touch it up.

 

Primers vary on permeability. Traditional primers are definitely porous. Their job is to bond to metal & provide a substrate that the color coat will adhere to. The color coat did the sealing & moisture exclusion.

However, some modern primers, especially the better self-etching ones like Dupont VariPrime seem to exclude moisture. Problem is nothing in the primer documentation/specs tells you that the primer excludes moisture or not.

Just get a small can of POR15 & paint the bare spot(s). It definitely excludes humidity & air.

 

a question I have is that I know of some shops that when refinishing "water sand" the primer...I have seen this done on the old grey lacquer based stuff (which is like a sponge)a and the newer tan glasuirite stuff. I tried water sanding the old grey stuff on an old buick once and in a week I had rust comming up through the primer (they used to say that you had to let it sit before sanding) I did etch it with one of the dupont etching liquids...so I am confused a little on water sanding primer/surfacers...Any insight?

 

Where'd the Rhino liner guy have to drill a hole? For the "Rhino Liner" badge?

Or does the Rhino Liner stuff fill in the factory drain holes to the point that it needs to be drilled out?

 

You gotta have at least two or three bondo/primer spots on your pickemup truck to be gin-u-wine.

Also you gotta let wax set up for a few days before buffing.

Dr "Deep in Dixie" Who

 

Wet sanding the primer is normal preparation for a seal coat followed by a color coat. The water will dry in a few minuites, depending on weather & humidity. However, often you also create some microscopic cut-thrus to the metal. They're only a problem if you don't protect them fairly quickly.

So, Once you wet sand, you've got at most a day or 2 to get a sealer or paint coat on, or recoat with a humidity resistant primer, before flash rusting starts to set in. If you've got a nice dry garage, with very low humidity (eg: A heated garage in MA in winter) you can go a week if necessary. Even up here going 2 weeks in the winter is pushing things. In summer, there's to much humidity. I don't like to go more than 24 hours before applying the next coat.

A day's exposure to rain will flash rust fer sure. At that point, you have to sand the primer off & start again.

The phosphate etches also only protect against flash rust for a couple of days unless the humidity is very low. Then you'll have to sand & re-etch.

 

Verell,
knew I could count on you to explain this.

best regards,
Paul

 

Uro,

Before you use the undercoat, use a good bare metal anti-rust primer. I use a primer called ZeroRust that works really well. I've also used Rustoleum Auto Primer with good success also. Once that dries, then top coat it with your paint or undercoating to seal it. If you don't used the anti-rust primer first, you may seal in moisture and find that your spot ends up rusting from the inside out.

Steve