Technical Epoxy Priming fresh blasted metal - a discussion.

So recently there’s been a discussion here about priming some fresh blasted metal.

The one side and manufacture tech sheet says to commercial blast the metal and prime the fresh blasted texture surface.

The other side says to 80 grit sand the blasting texture down to a smoother surface then prime it. The reasoning here is that it’s nearly impossible to wipe down the surface with any solvents, remove finger prints, or anything that may be stuck in the texture.


So the second position here makes more sense, involves a shit load more labor and violates the tech sheet.

What’s the best way?

 

I don't always read instructions, but when I do, I follow them.

 

Yep buzz it down with 80 grit for me.

 

The first time you see a fairly new (less than a couple of years old) paint job peel off in sheets, you'll wish you DA'd the surface before epoxy primer. Mechanical adhesion AND chemical adhesion is better than chemical adhesion alone.

 

I usually go with the instructions, unless I've had personal experience to dictate an adjustment in the recommendations. I blasted my coupe, epoxy primed, then surface primed, blocked and painted my coupe 25 years ago. No issues yet.

 

Blast, blow off with clean dry compressed air and prime immediately.

 

You want your parts to be media blasted with walnut shells or some other media. Sandblasting will do the job but it's way to aggressive for most parts. I just had several parts media blasted and you could run your hand over them they were so smooth. Leave the sandblasting for tombstones and graffiti removal.

 

You have ZERO recourse if you have issues down the road and didn't follow the TDS.

 

I usually blast, start doing body work, let it sit for a few years in my shop, then do some more bodywork, then when it's close I'll run a DA over it and throw on some urethane primer. Then more of the let sit/bodywork thing, etc.

It's nice living where it's dry

 

All this talk about sand blasting!! What grit do you use to remove paint down to bare metal, could it be that the blaster is in a hurry and is using 2 ought when he should be using 4 ought?
I've done my own blasting using 4 ought @ 100 psi and ended up with a glass smooth surface. Then lightly sand and a see through coat of etching primer, never had a paint job fail. Ralphie

 

Media and walnut shells certainly are useful in some applications but do not remove rust.
Media blasted parts are smooth indeed and require additional work to provide "tooth" for primer adhesion.

 

In the Northeast, rust capital, many of us use a coal waste product called Black Beauty.
The electric powerplants sell it.

 

Didn't you get some of the rain this weekend

 

This is how I do it, right or wrong and it works for me.

I sandblast the part/parts and then blow off any dust followed by using surface prep on the bare metal, I continue until the residue has been removed and clean it once more before spraying the etching primer.

Granted it's slow and time consuming but again, it works for me. HRP

 

There are different grits of sand blasting sand and the above mentioned Black Beauty. 80 grit is usually a medium grit of those. A good blast and prime is what I usually do when I have a rusty project. I will not blast for just paint removal.

 

25 yrs ago I was taught to blast then DP epoxy but I believe the product was better back then also I still have stuff that was done that way in1999 and no adhesion issues currently I use ppg industrial epoxy and do things the same way, I can’t imagine someone blasting a bridge then DA with 80 grit so I have kept my old methods for the most part , right or wrong

 

Seems like sanding defeats the purpose of creating a nice etch. Don't blast greasy or oily parts. Don't blast til you are ready to prime. Wear gloves when handling freshly blasted parts.
Works for me...

 

Didn't get any this weekend down here, but today it's rained 2.5 inches so far, flooding, roads closed, etc. Still not bad in the shop, I have good insulation.

 

Did my frame with that. I'm not an expert but it did a great job. Blasted, primed and painted.

 

Just did my 64' Polara last week . Recycled glass media 40-70 grit ( Dustless blasting) use Hold tight 102 in mix and then wash down with it when done,dry with compressor then leaf blower ,even drier air . I epoxy painted the underside of hood ,fenders, trunk e.c.t. that day with no prep. Next day hit all "finished sides" with 120 grit da then paint. Did the undersides first because if there was any flash rusting the finished side is way easier to run a da over then trying to get into all of the tight areas on the undersides.

 

I've been using black beauty (coal slag) for about 12 years. Only recently did I use a da and 80 grit after blasting. I had no adhesion problems in the past but the metal sure did look nice after the 80 grit pass. I use Kirker epoxy and have no complaints with it. I'm using the fine media and recycling it a few times which means it's way finer than the 1st usage. My thought about the da was that the metal is smoother. That should take less filler to achieve the desired end results. This whole subject has about 6 ways to get to the end. Some people take short cuts and get away with it and the others do everything as good as you can and the bird of paradise comes a long and takes the biggest dump ever on the paint job. Eventually, we all have to figure out what works in our shop and exp. level. Good luck to the O.P. You'll get it.

 

Anything used to blast material is "media". Sand, walnut shells, aluminum oxid, etc. are all different types of media.

Now what primer should be used on th fresh surface? Acid etch or epoxy? I lean towards epoxy. But I'm only an avid amateur so what do the no?

 

At our business Blastman, we’ be been blasting sheetmetal starting in ‘84. We use #80 garnet at about 65 psi. No pitting or warping! We offer to prime customer parts if wanted. PPG epoxy or for something’s Rustoleum. Old ( good) metal can sit a while if not touched. Good luck with that. We blast to bare metal & prime , depending on weather. ( we blast all inside & reuse material) good luck guys


Sent from my iPhone using H.A.M.B.

 

I have done it both ways, without problems, sanding leaves a SMOOTHER finish which in turn, leaves less sanding of the primer before paint.
I have noticed one thing about "raw" blasted metal, it does not weld as cleanly as a blasted piece that has been sanded. this leads me to believe there is still "sand" on the surface.

 

A friend of mine insisted that you should do most of your metal patching before blasting. For the reason you mentioned.

 

When I was doing my chassis stuff if a piece didn’t need mud... I would blast with fine coal slag, blow it off, epoxy prime wait an hour and then put the paint on. No sanding no touching the surface etc. it came out surprisingly smooth and had a great shine. Hope it holds up for a long time cause body work sucks to do.

 

I can almost guarantee there’s microscopic sand residue shit in the low spots of the texture profile.

This is the side I’m on.
However they wrote/write those things so that the verbiage will cover their ass not yours.

 

Just for general knowledge
What would these cost to get these items blasted
It was all clean metal that turned,
no paint, no undercoating.
Body , inside, outside, underneath on s cart.
Frame and rear axle.

 

In our part of the world "media" blasting uses the tiny plastic pellets which remove auto paint coatings leaving a smooth warp free but not rust free surface.
"Media" blasting really took off during the auto makers peeling clear coat days. It was the preferred method to remove the failed factory finish with less chance of damaging exterior components.
Other types of blasting are described more specifically as sand blasting, grit blasting, glass bead blasting, soda blasting, vapor blasting, walnut shell blasting etc and all have their uses.
To me acid etch primer is overkill used on a sand blasted surface.

 

31 Vicky........ What blasting material do you want used?