2K Prime not bonding to 1 piece

[jakeinsouthcarolina]

First - I don’t post here but do use all your posts and knowledge as my bible so thanks for that. Between posts here and help from Barry - I make do with my various projects.

I’m having the strangest issue. I have some new parts for a vintage Ford tractor. They all arrived with factory gray paint.

I sanded each piece with 120 grit and put a 2K primer over each piece. Of 16 pieces - 15 primed perfectly with a great bond but one fender will not accept the 2K. It literally just rejects it. I’ve tried twice with same result. Any ideas why and what to do next. Sand and epoxy prime ?

Any help is appreciated as I’m just stumped on this one piece. I did clean with soap and water and waterborne cleaner before spraying View attachment 7051

 

[El Toro]

Welcome May be some more detail and pics. just my 2 cents worth ......clean clean and clean again then strip to bare metal and epoxy. I take these are metal parts?

 

[Barry]

WOW! This is a head scratchier!
Don't know enough to even guess, raw metal, over sanded paint?
Pictures would help as I don't know where to start.

 

[jcclark]

I would guess it would have to be some kind of contamination issue on that
one fender. Some of these new car paint protect-ants that new car dealers are offering are really hard to get cleaned off.
Maybe something like that, only a farm type lubricant or sealer?
Whatever it is you'll have to get rid of it, and some are really tough, regular cleaners aren't strong enough.
My body shop guy says a product called "simple green" has worked for him.
I've used TSP (tri sodium phosphate)
If it's bad enough and it's not bare metal already, you may have to strip it.

 

[jakeinsouthcarolina]

I guess in the end I’ll just have to strip it and epoxy it. Just so strange that it was only one part and that it did it two times. The first time I thought I must not have cleaned it well enough but that shouldn’t have been the case the second.

Time for some elbow grease - down to bare metal. Can there be any 2k at all on the part before spraying epoxy or does it absolutely need to be free of it?

 

[jakeinsouthcarolina]

You know on further thought. Maybe I will try something like simple green. I’m just really curious to understand if it is some sort of imbedded contamination. Thanks for the posts. ... I’d still appreciate understanding if I can have a little 2k under epoxy or not.

 

[old soul]

I have had old laquer primer/paint bubble up like that in the corners and creases when I applied 2K (or epoxy) over it too heavily.
(Been a long time ago so can't remember if 2K or epoxy). I know that is probably not your problem since it only did it on one out of sixteen pieces but just putting it out there.

What is the blue stuff?

 

[Jim C]

old soul has touched on your issue. what is happening there is the primer or paint on the fender is not a catalyzed material. meaning its not a chemical resistant finish so when your applying your primer the paint underneath is soaking up the solvents. you primer is being sprayed too heavy so its drying on the surface while the original paint is soaking up and swelling making the splits you see. basically you have a hard crusty layer over a reliquified base that is moving. you would get the same thing if you shot 3 good coats of epoxy primer, let it sit an hour so it was flashed but not cured, then hammered on 2k primer over.

 

[jakeinsouthcarolina]

Old Souls and Jim C

Yes ! That has to be it !! When I sand I sand through my buff 2K then to the grey prime or paint that was on it and then underneath that there is some black paint or primer. As these are vintage tractor parts it’s absolutely possible this one was treated differently in some way

I quickly decided I’m not sanding down to bare metal on the whole thing (thought process moves very fast when you start sanding by hand and realize this is your wife’s old tractor after all)

I’m laying drop coats and will build slowly. Where the 2K bonded - it’s bonded very well.

I do see most of the bond failures in the creases and corners as Old Soul stated

I’ll report back tonight but thanks so much for the help

 

[jakeinsouthcarolina]

Well that didn’t work. Not sure I’ll ever get all the primer and paint off if that is required before epoxy. May be buying another fender

At least all the other pieces are primed, based, and cleared today !

 

[AAE]

Why not strip that thing to metal? It doesn't look that big. Might be worth it.

 

[old soul]

Just an observation of the pic in post #9... the one showing bare metal, black, blue and then white. That's a pretty ragged edge on the blue, as in it doesn't look like it feathered out if/when you sanded it. Poor adhesion. I'm with El Toro and AAE on this.... strip it.

 

[crashtech]

This is a great example of why it's dangerous to paint over other material that you're not sure of. At least in this case its revealing itself immediately, because believe me, you don't want to get it all done and then see it bubble up in the hot sun instead.

 

[jcclark]

I think if it was the paint you were going over , it would have done it on some of those other pieces as well.
It has to be something different on this panel verses the others.

 

[jakeinsouthcarolina]

I’ll strip it the best I can. You are right that feather looks rough but it didn’t feel rough.

I’m going to strip and epoxy today.

 

[jakeinsouthcarolina]

Just to close out the thread and say thanks. I think the epoxy worked. While I didn’t strip the whole panel - I did strip the center section where all my problems have been. I cleaned 4 times with Waterborne Cleaner and then sprayed 2 coats of SPI epoxy.

I layed the first coat of epoxy a little light and the second coat more normal with 30 min flash time in between. At 30 min after the second coat it looks like it will work. I do have some epoxy over both SPI 2K and a few spots of what I think is 60 year old enamel (grey)

Again many thanks for the help. This should be one nice 1958 Ford tractor for my wife when I get it back put together for her in a couple months.