Preventing Rust On sandblasted metal

[michaelp94]

Hello, new member here from Australia,

I've recently begun media blasting the boot of my project car and was wondering what I could use to prevent flash rust from forming on the freshly sandblasted metal. I plan to eventually weld some patch panels on some of the badly pitted metal but as I'm still practising welding and metal fabrication this may be a while.

When the metal has been welded and repaired, I plan on using POR15 to prevent further rust. If i apply the POR 15 metal ready prep (i believe its a phosphoric acid treatment) to the metal now after sandblasting, will this prevent the flash rusting until the POR15 paint is applied in the future? Is there any safety concerns with welding metal that has been treated with metal ready? Is there a cheaper alternative to this, I know there is weld through primer but it seems rather expensive to coat the sheet metal with as a rust prevention as i will be repeating this with both the floor pans and the engine bay?

Thanks for any help you can give,
Michael

 

[Burdekin]

Welcome to the forum.

If using POR you don't need to use metal ready to freshly blasted steel, you just need to clean it before painting. Metal ready also won't protect bare metal, it will probably make it rust worse if left untreated. Metal ready will neutralise light surface rust and etch the surface but needs to be cleaned thoroughly before over coating with paint.

Weld through primer isn't that good at preventing rust either, better than nothing but it will eventually rust. Okay for short durations.

I've used POR previously and had good results but I don't use it anymore. Personally I'd go for an epoxy mastic primer like Jotamastic 80 or something similar. After blasting, paint with epoxy mastic and then just remove the paint where you need to weld.

 

[the snooper]

i would have thought it would be better to get the welding out of the way first especially any pieces that you know about, that way you are only having to treat small areas at a time, then once the welding has been done blast it and use epoxy as said above

 

[vdubz]

I have used metal ready after blasting and its excellent at stopping any rust forming as it leaves a zinc coating, i have still got some parts stored in the garage that i blasted about 2 years ago and then sprayed with metal ready and they are still rust free.

 

[hairymel]

....it leaves a zinc coating....

i believe it is phosphoric acid which leaves a iron phosphate layer. seems popular in the usa and i have read several times that it will prevent flash rusting for a period of several years if the car is kept inside.