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Old 01-19-2022, 12:28 PM   #13
MP&C
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Re: Help with sanding after media blasting.

Most people today use an epoxy primer as the substrate to the bare metal as it offers the best protection against corrosion and rust creep. To the OP, what "media" was used?

As far as Eastwoods After Blast, it falls in the same category as Ospho and the other "cleaners" / "rust converters". They are not the end-all be-all authority on whether your epoxy primer will adhere to the conversion coating. Decide which primer/epoxy primer you plan on using and then check with THAT manufacturer to see if THEIR product is compatible with the phosphoric acid that is normally in these treatments..

From the Eastwood tech data sheet:

Quote:
NOTE: Phosphoric acid-based cleaner.
DO NOT allow product to dry on surface.
Speaking from experience, phosphoric acid residue left in the bottoms of deep pitting (the dry on surface disclaimer above..) will start to reactivate in hot sunlight (think car show) and within a year or two at the most, the chemical process that has started again will outgas and cause delamination above those pits.. You'll see it on the finished painted surface as raised circles about 1/16 to 1/8" diameter. Rework is not cheap so ensure compatibility with ALL products used before going down the rabbit hole of conversion coatings. As another thought, if we have media blasted, why do we need a rust conversion coating?

I personally prefer the garnet or coal slag media as they are for the most part inert and a proper cleaning with Wax and Grease remover will have you ready to spray epoxy without any acid treatments. The abraded surface already provides a nice surface for paint adhesion. Use caution using sand as a media, most sand also contains caustic salts that will get pounded into your metal. Another substance you don't want left under your paint.

Most all of the "easy" products have their own shortfalls, easy to ruin a fresh paint job without the whole story. My experience was my first exposure to ospho, the owner applied it in generous amounts to pitted panels as his buddy "used it all the time". I was just the painter. Bad when your name is on something that's got paint coming off. Even worse is when you have to eat the cost and labor, since Eastwood is not liable for the damage based on their disclaimer. Do your research, do it right, do it once.
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