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Old 01-15-2022, 06:49 PM   #1
desert-rat
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Help with sanding after media blasting.

Got some body panels back from being media blasted. Time to do some hammer & dolly work and fill in some holes.
The panels are rough because of the media blast. So how do I go about smoothing out the panels?? Some say DA. Some say by hand. But which grit sand paper?? Dry or wet?? Thanks.
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Old 01-15-2022, 07:02 PM   #2
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Re: Help with sanding after media blasting.

Whenever I have sand blasted body panels...I just wipe them real good with lacquer thinner, let fry, and shoot them with primer (give that they are rust free from blasting). That rough texture is fantastic for good primer adhesion. Any pitting from the rust can be given a few more coats of primer and then the all the primer can be sanded to smooth it out... Then I go after any body/dent work. Seal the all the blasted steel and then work it to get the dents out.
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Old 01-15-2022, 07:07 PM   #3
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Re: Help with sanding after media blasting.

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Old 01-15-2022, 07:46 PM   #4
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Re: Help with sanding after media blasting.

Dont use lacquer thinner to clean metal. Thinner has other ingredients in it and can lead to adhesion problems . It also dries way to fast to float the dirt and grease /silicones to be able to wipe them off with the follow up wipe. Best to use a dedicated wax and grease remover like Prep-all . You dont need to sand blasted areas I just hit it with Prep-all and then epoxy prime
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Old 01-15-2022, 07:55 PM   #5
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Re: Help with sanding after media blasting.

I'm with them.
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Old 01-15-2022, 08:24 PM   #6
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Re: Help with sanding after media blasting.

Thanks for chimin' in 72C20...Call me old school, but the last two projects I have done, I have used lacquer primer and have had not problem with adhesion after the fact. Not to mention, I tend to use more wipe down thinner than necessary.
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Old 01-15-2022, 11:20 PM   #7
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Re: Help with sanding after media blasting.

I am with the others. Wipe down good with a rag to get the lose stuff off. The wipe down with a good wax and grease remover. Then shoot a couple coats of epoxy primer on them.
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Old 01-16-2022, 10:54 AM   #8
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Re: Help with sanding after media blasting.

When ever you media blast something you need to first sand it down with 180 grit sandpaper via by hand or da. After media blasting the parts have like a scum on parts and this has to be removed, if you use lacquer thinner or any products it doesn’t remove this scum and adhesion problems will exist. Just a light scuffing of sanding with 180 grit is needed, you will see the product changing of appearance. Blow it off with pressurized air, then use a good quality epoxy primer. After this you may start your body straightening techniques. Thanks Chuck
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Old 01-16-2022, 02:06 PM   #9
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Re: Help with sanding after media blasting.

Things that I have had blasted that were extremely rough, I have usually sanded with 80 grit by hand or DA. Not real thorough either, just enough to make it where I can clean them easier without snagging on my rag/towel I'm wiping the wax and grease remover off with.
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Old 01-16-2022, 09:27 PM   #10
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Re: Help with sanding after media blasting.

I'm late here, but also agree with above..l had my whole truck sandblasted, the rough surface was perfect for spraying with epoxy primer..all I did was wax and degreaser, then spray..it was smooth after spraying...then I did my bodywork and sprayed over that with epoxy as well...then high build primer and paint
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Old 01-16-2022, 09:43 PM   #11
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Re: Help with sanding after media blasting.

lacquer thinner has water in it!!
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Old 01-19-2022, 11:24 AM   #12
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Re: Help with sanding after media blasting.

Maybe a little late to the party. Depending on the size of part, I spray with Eastwood's after blast stuff. It cleans and puts a protective coating on it. This allows me time to do any repairs without having to mix up primer. The stuff stinks so use in a ventilated area. Once all repairs are done, then I will use the after blast stuff and when I have enough parts I prime with some 2K high build. Eastwood also sells the 2k in a premix spray bomb if I am in a pinch. So far this method has worked out well.
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Old 01-19-2022, 12:28 PM   #13
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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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Old 02-10-2022, 06:52 PM   #14
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Re: Help with sanding after media blasting.

I would like to bring a few things to your attention. Zinc phosphate epoxy Automotive primer it's not The best defense against rust creap and corrosion . Automotive zinc epoxies after 700 hours of salt fog testing and then there will be rust creepage, Zinc Rich Industrial epoxy 3000 TO 5000 hours. Aluminum pigmented moisture cured urethane primers go 8000 of hours without any creepage Each epoxy manufacturer recommends different surface preps for bare metal some using acid etch some use wax and grease remover check the data sheet. Epoxy primer is not sunlight stable when it's exposed to heat and direct sunlight for any length of time it will continue to react that can cause a problem in the finish coat. All this information is available on the net
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Old 02-25-2022, 02:20 PM   #15
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Re: Help with sanding after media blasting.

I have used crushed glass to blast almost all of the sheet metal and other parts on my truck. It is a little slower than some of the other medias but it doesn't damage sheet metal and it leaves such a nice surface that it is well worth it. All I do is wipe it down while blowing with air and it is ready to epoxy prime. The primer lays down very smooth. I use a good 1:1 epoxy.
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