Does surface rust need to be removed?

blunosr · May 23, 2011

Hi, does minor surface rust need to be removed? It seems to me that we are told to remove all rust, then roughen up the surface to help new paint adhere. Wouldn't paint adhere and soak into a thin layer of surface rust and help the paint bind to the metal? So long as it is very dry when you paint. I'm thinking a well-thinned primer over dry surface rust, then good industrial paint.

Is there any logic to that?

I'm just finishing up a ditch digger for my Bobcat, and it's quite distressing how fast surface rust hits those new welds.

Thanks,

Troy

Allan in NE · May 23, 2011

Run your hand across that rust and then look at your hand. Notice how it comes right off?

Allan

Anonymous-0 · May 23, 2011

Since you brought up the topic, on farm shows they advertise a product I think they call "Rust Guy." Sounds too good to be true, they say if you apply it the metal "will never rust again". Can be left as is or painted. Anyone use it and how good is it?

Anonymous-0 · May 23, 2011

I would get rid of all rust before painting otherwise the rust will eventually show up thats only my opinion sandblasting is a wonderful thing

NCWayne · May 23, 2011

Rustoleium is making a product they call "rusty metal primer". It is designed to use in a situation like your describing where there is just a very thin 'dusting' of rust. The way I understand it does exactly what your talkin about in that it binds to the rust and further actually converts it to a primer. Then there are products like Marhyde, and other brands with different names that do the same thing, that do nothing but convert any lite rust to a primer. With it you then really need to prime over those areas so you'll have a uniform color under your paint. I've tried it on several things over the years and I can say for a fact it works. Beyond that a rust remover can be applied, or you can sandblast it to get the rust off but in the end you don't want to paint over rust with regular paint as the rust will eventually pop right through.

BCnT · May 23, 2011

only thing i know for a fact is OSPHO is the only rust convertor thats been around as long as me and WORKED curing Galveston Island Cancer.
used many a gallon on rusty steel in Todd's Shipyard and repairing rust damage on my own cars and trucks...the newer stuff may work as good but its about 3 times the price of OSPHO from what i've seen.
brush off loose rust and spray/brush on OSPHO...let it dry...it develops a black/gray phophate coating...before painting wire brush loose coating off and shoot with your favorite primer and paint.
it will not rust if you dont get around to painting for 6 months or more.

DaveK(IN) · May 23, 2011

Did you do any work on the Big T? My dad was in charge of that building project and very proud of it. I bet the folks on the forum would enjoy seeing a picture of "big iron". Do you know what became of it when the yard closed?

Wardner · May 23, 2011

The Connecticut Dept of Highways did field testing on newly blasted bridge steel that suffered oxide contamination from rain. This would be first stage oxidation. They determined that the rust did not have to be removed. This testing was done over 20 years ago.

Bear in mind that ferrous rust has four different chemical signatures. The molecule adds an oxygen atom over time. The last stage has four oxygen atoms. Later stage oxidation was not tested as they assumed their contractors would repaint before the second stage or face a mandatory reblast. Ya, I have painted a few bridges.

Mike M · May 23, 2011

I have tried a few of those "miracal" rust converters. I'm not at all impressed !

Best way is to sand blast,blow off the dust and then paint right away.

BCnT · May 23, 2011

if you're talking about the drydock i believe the company that bought out Todd's used it till they went belly up...saw a special year or so back about companies salvaging stuff along the gulf coast...they had managed to cut the drydock in half for salvage and tried to float the halves out...one half sunk in the middle of the Galveston Channel and they had a helluva time re-floating it.
any pictures i had have long since been lost during moves...left Galveston over 30 years ago and aint missed it a bit...took awhile to get used to having a truck outlast the engine instead of having the body crumble around me.

Does surface rust need to be removed?

blunosr

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Allan in NE

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Anonymous-0

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Anonymous-0

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NCWayne

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BCnT

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DaveK(IN)

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Wardner

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Mike M

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BCnT

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