Technical An epoxy primer adhesion failure?

So far.

When dealing with instruction sheets and recommendations we must never forget the manufacturer's covering their *** elements. They have no idea what you have done. Their guidelines are generally speaking, and when they mention prep procedures it never means use all the procedures covered to be used. It's very easy to work so hard at something out of caution that you cause more grief. My preferred bare metal process is chemical strip and metal prep. In all my years I never had purified metal "go bad" in the time it took to get it covered. Mind you, I didn't let **** sit outdoors for days or weeks after. I always neutralized with the hottest water I could stand as well. Heat, evaporation, fast dry. Over the last 15-20 years there seems to be a m*** panic over bare metal within this industry. Can't put filler on it, cover it up IMMEDIATELY in epoxy, flash rust is warned of. WTF, are we working in the rain? Rinse, air, sometimes heat gun or propane torch for seams. DRY, period. I hate wiping bare metal with a cloth, especially blasted. Yeah I want all those fibers under it, right? If I'm going over blasted metal it gets hand brushed and lots of air, I tend to use slow solvents too for a good "soak" into the texture.

My goal is to present the logical approach vs excessive caution. How come we find OEM old cars with original paint given the speed and simplicity of the manufacturing process?
I'd bet my 39 Ford (with original paint) Henry didn't spend the prep time some do nowadays. Why is that ****ty no good Ford paint still there and shiny? Pragmatism is ****in awesome. Basics never fail. Logic is not a Mr Spock exclusive.
And yes I am a smart *** with a ****ty bedside manner but I won't ******** you, nor anyone else.

 

I have two friends who had a similar experience. They strip to bare metal using a DA or "Hamburger Patty" abrasive wheel after sandblasting so that they know they are applying to bare metal. If you take a sandblasted panel and rub it with sandpaper, you get all sorts of stuff coming off of it before you get to shiny metal. I'm not paint expert but these guys swear they will never apply primer directly to sandblasted steel again. YMMV

@MP&C , I'd love to hear your input on this.

 

Sandblasted metal is dirty. White rag it...

I prep Sandblasted metal before tig welding because of the dusty film and it makes a difference.

I just don't feel comfortable going directly over it without doing a wipedown. But apparently others do.

We had a compressor lose a seal on a bridge job, blew a mist of oil over the entire deck. Didn't realize it had even happened until they started washing the deck and noticed the oily residue.

 

I always follow blasting with #80 then #220 grit on the DA to remove any remnants of blasting from the surface followed by a wax/grease remover wipe down and have never had a primer adhesion problem.

 

I used same method and Products for this black cab. No issues, I do like the price of Kirker for my purposes as it will get top coat.
FYI Kirker epoxy primer not resistant to brake fluid I learned..

 

i think the epoxy and filler bonded very well, when you hammered around the filler - and cracked it- the well adhered primer lifted with the filler.

 

This is what I "think" as well. When I stretched the metal back out it changed the radius of that bend. The metal flexed and the filler didn't. Epoxy had to stick to one...and it was the filler. The failure is literally only in the radius.

But I can't say for sure...that's why I asked the question here hoping someone had experienced something similar.

 

Sandblasting is an air forced method of abrasive stripping. If you do soda it can be a big mess. I like to hot water wash soda blasted stuff which I usually reserve for aluminum or carb parts, then some hot water and Dawn dish soap, and a heavy rinse followed by lots of air to dry well. Sheet metal, after blasting I take a stiff plastic brush and high pressure air, get the grits out the pits, cuz that's what you get, a micro pitted surface. I prefer an experienced media blaster but that's no guarantee of zero warpage. Here's another process. I do all the welding and panel replacement BEFORE the thing is stripped. Why? Well I like the welds and minor divots cleaned up too. As good as you are at metal and welding work there's sure to be some little gremlin spot that needs cleaning. Pragmatic, no? For the record I'm not saying "you ****ed up," I suspect you're more a victim here. And true enuff everybody needs to do their own gig but sometimes the extra steps don't always err on the side of caution.

I also don't like a whole car frosted like a ****in birthday cake with mud. If that hammering cracked what you have there how many heat cycles will crack the outside finish? I don't wanna find out, but that's another topic.

 

I agree with blasting after metal work. You find pinholes that you didn't know were there. It also ensures some tooth in places you can't get a DA or manually get to.

 

Any collision repair estimator or body man sees the results of even minor impact on metal, with varying degrees of adhesion being compromised. If not hammered on, chances are this condition may not have ever been noticed. We have all done it; backtracked to correct a high/low or other defect before paint. Take precautions and backtrack the whole way to the base metal on any areas worked.
Wax and grease removers should be used prior to any paint removal or metal work to eliminate any spreading or permeation. The exception I suppose would be a vehicle left in a less than oil or other contaminant free environment for an extended time period. As hobbyists, we tend to work on one section at a time over a period of time. Many times, we have seen the detrimental effects of a vehicle being stored where other work has been done using oil, silicone or other products that will permeate the air and settle on everything. Ever leave the cap off a jug of muriatic acid in the same garage? Just using air tools lubricated with oil can disperse a fine mist that could cause grief if precautions are not taken. A good 'prime wash' before paint is always good practice but as well between processes if possible contamination has occurred.
Like others I prefer a sanding after sandblasting to remove the trapped material and uneven surfaces that are prone to snagging fibers from wiping cloths.
I usually follow that with a thorough 'wet' wipe down prior to any coatings being applied. Just a few things to keep in mind.

 

Agree 100%!

Mine sits in a shop for weeks before I can work on it. Kids fingers, dogs, other projects...wood dust, abrasive dust etc.

I feel like wax and grease remover is a must after it has sit...

 

Allways D.A. your bear metal with 80 grit to get a etch, metal wash, acid etch, 2K prime then do your repair . Its been said a few times on this thread and there 100% wright .

 

It was DAd. However I'm sure that reverse curve wasn't..