My brothers have a 20 foot equipment trailer that is in need of a re-spray. They will be using a pressure washer sand plaster to remove the old paint, rust and scale.
The problem is the immediate flash rust that will occur. What can we coat it with to nutralize the rust? This isn't a concoarse paint job. We need to balence cost with ease of use.
What say GRM?
Primer.
Primer kills flash rust?
What about spray on rust converter? I'm a little confused by flash rust, even things I've pulled from electrolysis tanks took a day or two to start rusting again.
Is it just surface rust or does it flash penetrate?
The pressure washer set-up leaves water on the now bare metal. With 20 feet of trailer, plus crossmembers, ect... we'd probably use gallons of rust converter. It is in Montana, so the humidity is only 20-25% on an average day.
Many a primer is stable on flash rust.
Rustoleum rusty metal primer? What paint are you planning on?
Vinegar. Vinegar. Vinegar.
Do the Google 
Metal etching acid (normally hydrochloride I believe) will greatly reduce rusting, and of course remove any surface rust. Similar to vinegar, but more powerful. Home Depot sells it by the gallon for pretty cheap. You clean off the acid with water, so you can just fire up the washer again (about half an hour seems to work good).
I had parts of a car stripped to metal in my garage. After etching the metal, it sat, covered, un-rusted for months. Of note, I am in California, about 10 miles from the coast, so it's pretty low humidity. I did notice that exposed metal near the door would surface rust in a few days / weeks (morning mist / fog).
phosphoric acid
This is sold at building supply stores as "Concrete cleaner/etcher" It's better then hydrochloric acid which is also sold as a concrete etcher & rust remover. Phosphoric acid if left on will leave a coating that is a good base for primer or paint. I mix it with 3-4 parts water and spray it on lightly rusted metal. Once I clean it I re-spray and let it dry. When you're ready to paint just wipe the surface down with a solvent and paint.
aircooled wrote: Metal etching acid (normally hydrochloride I believe) will greatly reduce rusting, and of course remove any surface rust.
Yes, hydrochloric acid - usually called muriatic acid in the building trades, also used for etching concrete.
hydrochloric/ muriatic acid cleans rust out down to the berkeleying pore level in steel but will start rusting immediately after washing off/ neutralizing w/ water.
excellent weld prep on steel, particularly TIG. If ever a weld could 'smell that clean' it was after acid prep. 
Ospho is what I used on the bus. It's about $12 a qt and if you are spraying it, it will go a long way.
I prefer to avoid using harsh chemicals. So if I thought it needed more than just a quick coat of primer, I'd probably give it a once over with some Scotch-Brite pads to mitigate flash rust and then prime it. But apparently I also like doing things the hard way.
They'll probably use cheap tractor paint. This is a construction trailer that lived it's life in Illinois so you can imagine the scaly rust. Concrete etch is probably what they'll go with.
Turboeric wrote:aircooled wrote: Metal etching acid (normally hydrochloride I believe) will greatly reduce rusting, and of course remove any surface rust.Yes, hydrochloric acid - usually called muriatic acid in the building trades, also used for etching concrete.
Also found in swimming pool stores
Should be noted that phosphoric acid is usually the key ingredient in all those rust converter/naval jelly products.
An acid wash to remove flash rust leaves flash rust when you wash it off. It will also screw up the paint if it's not scrupulously cleaned away.
Sine_Qua_Non wrote:Turboeric wrote:Also found in swimming pool storesaircooled wrote: Metal etching acid (normally hydrochloride I believe) will greatly reduce rusting, and of course remove any surface rust.Yes, hydrochloric acid - usually called muriatic acid in the building trades, also used for etching concrete.
Not that it matters, since Phosphoric is the one you would actually want to use.
Just grab a leaf blower after you wash it blow it as dry as you can an forget about primer just squirt it with Tractor paint thinned and catalyzed per the paint the next day. $50 for a gallon and a half of mixed and thinned and catalyzed paint.
If you really want to put something down just spray on some thinner and let that evap hours before you paint.
You'll need to log in to post.
