View Full Version : Cast Iron & Rust

Brian Effinger
07-17-2008, 3:28 PM
Hi everyone. I have a rust removal project & need some advice. I have to remove the surface rust from these 2 cast iron urns


and then prime & paint them. Should I remove every last trace of rust, or can some of the stubborn spots remain under the new paint job? Will they continue to rust under the paint? As you can see, I've made good progress on the urn on the right, but there are still some rust stains. I want to do the right thing here, because they are for either side of my father-in-law's headstone.

Any help would be appreciated. :)

Matt Ocel
07-17-2008, 6:19 PM
I'd sandblast, prime, then paint.

Brian Effinger
07-17-2008, 8:51 PM
I'd sandblast, prime, then paint.

Unfortunately, no sandblaster. For me it's the old fashioned way of steel wool and elbow grease.

Tom Hamilton
07-17-2008, 10:12 PM
Brian, phosphoric acid will kill the rust, Dead! Then you can paint without fear of the rust coming back.

In the paint department at the Borg, look for gallon containers of Phos-O-Rust or other similar sounding products containing phosphoric acid.

Build a box slightly larger than the urn, put a trash bag in it and sit the urn down in side. Pour in the phosphoric acid. It will probably take several gallons.

The next morning put the other urn in the tank. When they are done cooking you can scrub the film off with a scotch brite and water. Yea, water, they won't rust again. Then when dry, spray with Krylon or your favorite rattle can. SCHAZZAMM, your a hero! Oh, save the phosphoric acid for the planes, chisels, and other rusty stuff that will come along. It has a long life.

Tom, in Houston, wondering what you will plant in your new urns.

Matt Ocel
07-17-2008, 10:20 PM
"Elbow grease"

Does anyone under 30 know what that is?

David G Baker
07-17-2008, 11:36 PM
Phosphoric acid as Tom wrote. I have never purchased it from a Borg, I always purchased mine directly from the ZEP salesman. The only thing you might want to experiment with is the ratio of acid to water, you may be able to dilute the acid. I have used swimming pool acid (muriatic acid which is diluted hydrochloric acid I believe) but again it needs to be diluted. One other thing, the metal may flash rust after cleaning so you may need to protect the metal until it can be painted. I used water soluble oil.